Accepted Manuscript

Formation characterization and computational studies of mono- and dinuclearrhenium(I) chromone compounds

Ifeoma Ebinumoliseh Irvin Noel Booysen Matthew Piers Akerman Bheki Xulu

PII S0022-2860(16)30592-0

DOI 101016jmolstruc201606018

Reference MOLSTR 22637

To appear in Journal of Molecular Structure

Received Date 13 April 2016

Revised Date 5 June 2016

Accepted Date 5 June 2016

Please cite this article as I Ebinumoliseh IN Booysen MP Akerman B Xulu Formationcharacterization and computational studies of mono- and dinuclear rhenium(I) chromone compoundsJournal of Molecular Structure (2016) doi 101016jmolstruc201606018

This is a PDF file of an unedited manuscript that has been accepted for publication As a service toour customers we are providing this early version of the manuscript The manuscript will undergocopyediting typesetting and review of the resulting proof before it is published in its final form Pleasenote that during the production process errors may be discovered which could affect the content and alllegal disclaimers that apply to the journal pertain

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Formation characterization and computational studies of

mono- and dinuclear Rhenium(I) Chromone compounds

Ifeoma Ebinumoliseh a Irvin Noel Booysen a Matthew Piers Akermana Bheki

Xulua

a School of Chemistry and Physics University of KwaZulu-Natal Private Bag X01 Scottsville 3209

Pietermaritzburg South Africa

Abstract

Herein we report the formation and characterization of a novel dinuclear rhenium(I)

compound fac-(Re(CO)3Br)2(micro-chret) (1) [chret = N Nlsquo-bis(2-amino-3-

imino)methylenechromone-12-ethane] and a mononuclear metal complex fac-

[Re(CO)3(bzch)Br] (2) [bzch = 2-benzimidazole-4H-chromen-4-one] The metal

complexes were characterized by 1H NMR- IR- UV-Vis melting point and

conductivity measurements The solid-state structures for 1 and 2 were confirmed

via single crystal X-ray analysis X-ray studies of 2 revealed the transformation of the

chb diimine into the bzch chelator (in 2) The simulated IR spectra for the respective

metal complexes provided insight in the interpretation of their corresponding

experimental spectra

Keywords Rhenium Chromone Spectral Characterization DFT Studies Crystal

structure

Corresponding author Booyseniukznacza

1 Introduction

The considerable attention received by the coordination chemistry of rhenium

stems from the ideal properties of its 186- and 188-radionuclides which are well

suited for radiotherapy [1-3] For example the bone-targeting therapeutic

radiopharmaceutical rhenium-HEDP (HEDP = hydroxyethylidene disphosphonate)

has several advantages over the commercially available alternatives in terms of

efficacy safety and the ability to be produced on site allowing for the rapid

treatment of patients with painful bone metastases [4] Furthermore the facial

tricarbonylrhenium(I) core has shown to serve as an ideal synthon for the

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formulation of new rhenium radiopharmaceuticals This is illustrated by the facial

tricarbonylrhenium(I) complexes stability under physiological conditions where the

small size of the fac-[Re(CO)3]+ core allows binding to various biological entities [5-

6] However the next generation of potential rhenium radiopharmaceuticals requires

chelators which can stabilize the metal centre both in the low and high oxidation

states [7] Furthermore these multidentate chelators should also cater for the

inclusion of biologically active moieties which may aid in the target specific

biodistribution of the metallopharmaceuticals [8 9]

In our previous studies we have reported the isolation of oxorhenium(V) and

facial tricarbonylrhenium(I) complexes with Schiff bases encompassing uracil

chromone or benz(othiazoleimidazole) moieties [10-12] These multidentate Schiff

base chelators illustrated diverse coordination behaviours leading to mono- or

dinuclear rhenium compounds For example an unique dinuclear rhenium(I)

complex (micro-bzp)2[Re(CO)3]2 [Hbzp = N-(2-hydroxybenzylidene)-benzimidazole] has

a centralized 8-membered chelate ring formed by coordination of the benzimidazole

nitrogens to the individual rhenium atoms [11] Furthermore different

transformations of the chromone mono-imines 2-(2-thiolphenyliminomethyl)-4H-

chromen-4-one (Htch) and H3uch [5-((4-hydroxy-2-methoxy-2H-chromen-3-

yl)methyleneamino)-6-amino-13-dimethylpyrimidine-24(1H 3H)-dione] were

observed upon their coordination reactions with trans-[ReOBr3(PPh3)3] to afford

[ReO(Hns)] H2ns = bis-[(2-phenylthiolate)iminomethyl]-methyl-1-(2-

hydroxyphenyl)prop-2-en-1-one and [ReO(OCH3)(PPh3)(Huch)] [12]

As a continuation of our research studies on rhenium herein we consider the

coordination behaviours of multidentate diimines encompassing chromone moieties

This secondary metabolite chromone and its derivatives are known to induce

cytotoxic effects in breast cancer cell lines [13 14] Hence we report the coordination

reactions of [Re(CO)5Br] with the diimines N Nlsquo-bis(2-amino-3-

imino)methylenechromone-12-ethane (chret) and NNrsquo-bis((3-chromone)methylene)-

benzene-12-diamine (chb) to afford a novel dinuclear rhenium(I) compound fac-

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(Re(CO)3Br)2(micro-chret) (1) and a mononuclear compound fac-[Re(CO)3(bzch)Br] (2)

[bzch = 2-benzimidazole-4H-chromen-4-one]

N NO

O

O

Ochb

N NO

O

O

O

chret

NH2 H2N

N

HNO

O

bzch

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2 Experimental

21 Materials and methods

The reagents bromopentacarbonylrhenium(I) ethylenediamine

12-diaminobenzene 2-amino-3-formylchromone and 3-formylchromone were

obtained from Sigma Aldrich and used as received All solvents and common salts

were obtained from Merck SA Reagent grade toluene was dried over sodium wire

solvents were used without further purification The synthetic procedure and

characterization data for the free-ligand chret can be found in the online supporting

information document see Figs S1 S2 and S5 The diimine chb was obtained from

the condensation reaction of 12-diaminobenzene with a two-fold molar quantity of

3-formylchromone [15]

The infrared spectra were recorded on a Perkin-Elmer 100 spectrometer in the

4000 ndash 450 cm-1 range The 1H NMR spectra were obtained using a Bruker Avance

400 MHz spectrometer All NMR spectra were recorded in deuterated

dimethylsulphoxide UV-Vis spectra were recorded using a Perkin Elmer Lambda

25 The extinction coefficients (ε) are given in dm3mol-1cm-1 Melting points were

determined using a Stuart SMP3 melting point apparatus The conductivity

measurements were determined at 295K on a Radiometer R21M127CDM 230

conductivity and pH meter

22 fac-(Re(CO)3Br)2(micro-chret) (1)

A 11 molar reaction mixture of [Re(CO)5Br] (0050 g 0123 mmol) and chret (0049 g

0123 mmol) in 15 cm3 of anhydrous toluene was heated at reflux under nitrogen for

4 hrs The resultant reaction mixture was cooled to room temperature and filtered

An orange precipitate was dried under vacuum Pale orange X-ray quality

crystalline parallelograms were obtained from layering the precipitate with a 11

(vv) THFhexane over a period of five days MP = 215 - 220 ᴼC yield = 87

Conductivity (DMSO 10-3M) 1693 ohmcm2mol-1 IR (νmaxcm-1) ν(N-H) 2920 2850

(m) ν(CequivO) 2015 1871 (vs) ν(C=O) 1655 (s) ν(C=N) 1615 1613 (s) ν(O-C-O) 1464

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cm-1 (s) 1H NMR (295 K ppm) 1091 (br s 4H 2x NH2) 895 ndash 865 (m 6H H10

H12 H16 H19 H24 H26) 812 ndash 711 (m 4H H9 H11 H23 H25) 469 ndash 439 (m 4H

H17 H17rsquo H18 H18rsquo) UV-Vis (DMSO λmax(K M-1cm-1)) 269 nm (24159) 296 nm (sh

20140) 405 nm (sh 2464)

23 fac-[Re(CO)3(bzch)Br] (2)

The equimolar coordination reaction between [Re(CO)5Br] (0050 g 0123 mmol) and

chb (0052 g 0123 mmol) was conducted in 15 cm3 of anhydrous toluene heated at

reflux under nitrogen for 4 hrs The resultant reaction mixture was cooled to room

temperature and an orange precipitate was filtered and dried under vacuum Pale

orange cubic crystals suitable for X-ray analysis were obtained from dissolving the

precipitate in tetrahydrofuran and layering with hexane MP = 210 ndash 211 ᴼC yield =

93 Conductivity (DMSO 10-3M) 2372 ohmcm2mol-1 IR (νmaxcm-1) ν(N-H) 2915

(w) ν(CequivO) 2015 1871 (vs) ν(C=O) 1628 1607 (s) ν(C=N) 1567 (s) ν(O-C-O) 1461 (s) 1H NMR (295 K ppm) 969 (s 1H H1) 939 (s 1H NH) 827-722 (m 8H H3 H4

H5 H6 H12 H13 H14 H15) UV-Vis (DMSO λmax(K M-1cm-1)) 275 nm (sh 26107)

282 nm (27295) 309 nm (sh 22025) 394 nm (6614) 418 nm (sh 4394)

24 X-ray diffraction

The X-ray data for C28H18Br2N4O10Re23(C4H8O) and C19H10BrN2O5ReC7H8 were

recorded on a Bruker Apex Duo equipped with an Oxford Instruments Cryojet

operating at 100(2) K and an Incoatec microsource operating at 30W power Crystal

and structure refinement data are given in Table 1 Selected bond lengths and

angles are given in Tables 2 and 3 In both cases the data were collected with Mo Kα

(λ = 071073 Aring) radiation at a crystal-to-detector distance of 50 mm The following

conditions were used for data collection omega and phi scans with exposures taken

at 30 W X-ray power and 050ordm frame widths using APEX2 [16] The data were

reduced with the program SAINT [16] using outlier rejection scan speed scaling as

well as standard Lorentz and polarization correction factors A SADABS semi-

empirical multi-scan absorption correction [17] was applied to the data Direct

methods SHELX-2014 [18] and WinGX [19] were used to solve both structures All

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non-hydrogen atoms were located in the difference density map and refined

anisotropically with SHELX-2014 [20] All hydrogen atoms were included as

idealised contributors in the least squares process Their positions were calculated

using a standard riding model with C-Haromatic distances of 093 Aring and Uiso = 12 Ueq

C-Hmethylene distances of 099 Aring and Uiso = 12 Ueq and CndashHmethyl distances of 098 Aring and

Uiso = 15 Ueq The amine hydrogen atoms were located in the difference density

map and allowed to refine isotropically

25 Computational details

Molecular simulations were conducted with GAUSSIAN 09W [20] Geometry

optimizations of 1 and 2 were achieved through a DFT calculation using the B3LYP

functional with an accompanying hybrid basis set viz the 6-311G++ (d p) basis set

was applied to all the C H N O and Br and the LANL2DZ basis set which makes

use of effective core potentials applied to the metal centre [12] Prior to the

calculation the solvent molecules of recrystallization for the respective metal

complexes were omitted from their crystal structures and the resultant structures

were used as the starting conformers Good agreement was found between the

optimized and experimental geometrical parameters (refer to Tables 2 and 3) with

the minor deviations attributed to the fact that the gas phase optimized structures do

not account for intermolecular interactions or any short distance contacts The close

correlation between the optimized and geometrical parameters of the respective

complexes is further emphasized by the low calculated root-mean-square deviation

(RMSD) see Fig 1 The larger RMSD of 1 is mainly ascribed to the largely free

rotation of the C-C single bonds within the chret chelator Using the optimized

structure of the metal complex the lack of any negative Eigen values in the

frequency calculations confirmed that the structures are at global minima on their

individual potential energy surfaces [21]

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Fig 1 Overlay structures of the optimized and experimental crystal structures for the

respective complexes with their corresponding RMSD values The crystal structures are

shown in yellow while the optimized structures are given in blue

3 Results and Discussion

31 Synthesis spectral characterization and computational studies

The metallic compounds fac-(Re(CO)3Br)2(micro-chret) (1) and fac-

[Re(CO)3(bzch)Br] (2) [bzch = 2-benzimidazole-4H-chromen-4-one] were synthesized

under anaerobic conditions from the equimolar reaction of [Re(CO)5Br] with the

diimines chret and chb respectively In 1 the chret ligand bridges two fac-

[Re(CO)3Br] units while coordinating as a bidentate moiety to each metal centre via

its NiminoOketo donor sets Despite the use of anaerobic conditions X-ray studies of 2

revealed that the chb diimine underwent intraligand cyclization followed by the

hydrolysis of one of its imine bonds In fact the chloro rhenium(I) analogue fac-

[Re(CO)3(bzch)Cl] was similarly formed from the reaction of [Re(CO)5Cl] with the

Schiff base ligand 2-(2- aminophenyliminomethyl)-4H-chromen-4-one (H2pch) which

led to the transformation of the latter to a bzch moiety [11] However no

transformation of the diimine chb occured in the dinuclear ruthenium(III)

compound (micro-chb)[mer-RuCl3(PPh3)]2 where the neutral chb moiety bridges the two

cis-[RuIIICl3] cores via its ketonic oxygen and imino nitrogen atoms [15] In contrast

to 2rsquos centralized 1 2-((methylene)imino)-benzene moiety the flexible

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((imino)methylene)-12-ethane bridging moiety of 1 minimizes steric strain within its

chret chelator which effectively induces stability and prevents the transformation of

the chret ligand Furthermore compounds 1 and 2 exhibits good solubility in high

boiling point polar solvents including dimethylsulfoxide and dimethylformamide

while showing a relatively modest solubility in tetrahydrofuran and poor solubility

in chlorinated solvents such as chloroform The low molar conductivities [ΛM = 1693

and 2372 ohmcm2mol-1] of the metallic compounds indicates their neutrality in

DMSO

Broad vibrational bands are observed below 1700 cm-1 in the experimental IR

spectra of the metal complexes which could not be clearly assigned without the aid

of the simulated IR spectra of 1 and 2 see Figs S1 ndash S4 Both the experimental [2015

1871 cm-1 for 1 and 2] and simulated [2105 2018 2016 cm-1 for 1 and 2097 2017 1993

cm-1 for 2] IR spectra are dominated by the intense stretches of the carbonyl co-

ligands Similarly the ν(N-H) vibrations of 1 and 2 appear as weak intensity

vibrational bands in their respective simulated [3644 cm-1 for 1 and 3654 3289 cm-1

for 2] and experimental [2920 2850 cm-1 for 1 and 2915 cm-1 for 2] IR spectra The

simulated IR spectrum of 1 indicates distinctive vibrational bands associated with

the ketonic (at 1687 cm-1) imine (at 1567 cm-1) and ether (at 1469 cm-1) bonds

whereas the corresponding IR stretching frequencies can be found at 1655 cm-1 [for

ν(C=O)] 1464 cm-1 1615 [for ν(O-C-O)] and 1613 cm-1 [for ν(C=N)] in the

experimental IR spectrum of 1 Correlating the simulated IR spectrum of 2 with its

experimental IR spectrum revealed that the experimental vibrations for ν(C=O) are

found at 1628 and 1607 cm-1 while ν(C=N) and ν(O-C-O) appears at 1567 cm-1 and

1461 cm-1 respectively

In the proton NMR spectrum of 1 the aliphatic protons of the bridging ethane

moiety resonates as a multiplet between 469 and 439 ppm see Fig S6 A broad

singlet at 1091 ppm corresponds to the protons of the amino nitrogens of 1 but the

analogous protons were observed as two broad signals in the proton NMR spectrum

of the free-ligand chret see Fig S5 For 1 the aromatic protons of the chromone

moieties and the imino signal coalesce into two multiplets (viz 895 ndash 865 ppm and

812 ndash 711 ppm) in comparison to the corresponding well-resolved signals at 872

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ppm (for the imino protons) and 798 767 737 ppm (for the aromatic protons of the

chromone moieties) of the free-ligand chret The most intense signal in the 1H NMR

spectrum of 2 is due to the H1 proton positioned on the chromone moiety which

appears as a sharp singlet (at 969 ppm)

The benzimidazole proton in 2 resonates as an intense signal at 939 ppm

which integrates to one while the multiplet between 827 and 722 ppm are due to

the remaining aromatic peaks The presence of the pi-conjugated neutral chelators in

1 and 2 results in the occurrence of only intra-ligand - transitions in their UV-Vis

spectra see Figs S7 and S8 As expected no metal-based d-d transitions are

observed at more red-shifted regions due to the low-spin d6 electron configurations

of 1 and 2

32 Crystal structure of 1

Compound 1 co-crystallized with three tetrahydrofuran molecules of

recrystallization in its triclinic unit cell The crystal lattice of 1 is stabilized by a

network of classical intramolecular [Br1H4a-N4 = 273(4) Aring and Br2H2a-N2 =

260(4) Aring] and intermolecular hydrogen bonding [O11AH2b-N2 = 195(4) Aring and

O11BH4b-N4 = 191(5) Aring] see Fig S9 Collectively these hydrogen bonding

interactions allows molecules of 1 to pack in columns parallel to the [a]- and [b]-axes

The metal centres of 1 are positioned in the centre of the distorted

octahedrons which are largely imposed on by their constrained bite angles [O1-Re1-

N1 = 8452(7)ordm and N3-Re2-O6 = 8393(7)ordm] see Fig 2 Consequently the C2-Re1-Br1

[17685(8)ordm] O1-Re1-C3 [17741(9)ordm] C1-Re1-N1 [1762(1)ordm] Br2-Re2-C6 [17699(8)ordm]

C4-Re2-O6 [17641(9)ordm] and N3-Re2-C5 [1742(1)ordm] deviate all from linearity The

flexibility of the bridging ethane moiety affords narrower C=N-C [C18-N3-C19 =

1148(2)ordm and C16-N1-C17 = 1150(2)ordm] bond angles than the expected 120ordm for a bond

angle containing a central sp2 hybridized nitrogen Despite the influence of the

bridging ethane moiety the imino bonds [C16-N1 = 1286(4) Aring and C19-N3 =

1291(4) Aring] of 1 are in the range [1285(3) - 1312(6) Aring] observed for similar bonds

found in other Schiff bases [7 11 21 22 23] Across the respective octahedrons only

the Re1-C2 [1894(3) Aring] and Re2-C6 [1893(3) Aring] bonds are nearly equidistant which

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reflects similar trans-influence induced by the Br1 and Br2 atoms respectively

Hence the comparable cis-orientated organometallic bonds [Re1-C1 = 1942(3) Aring

Re1-C3 = 1897(3) Aring Re2-C4 = 1908(3) Aring and Re2-C5 = 1932(3) Aring] across the

octahedrons in 1 differs

The rhenium to ketonic [Re1-O1 = 2137(2) Aring and Re2-O6 = 2139(2) Aring] and

imino nitrogen [Re1-N1 = 2169(2) Aring and Re2-N3 = 2171(2) Aring] bonds are similar to

analogous bonds found within fac-[Re(CO)3(chrpychr)Br] (chrpychr = 2-(4-oxo-4H-

chromen-3-yl)-5H-chromeno[23-d]pyrimidin-5-one) and [(micro-O)ReOCl(amp)2]

(amp= 6-amino-3-methyl-1-phenyl-4-azahept-2-ene-1-one) [24 25] Bond orders with

the chret chelator is established based on the ketonic bonds [C14-O1 = 1259(4) Aring and

C28-O6 = 1261(3) Aring] being longer than the carbonyl bonds [eg C1-O3 = 1144(3) Aring]

but yet shorter than the ether bonds [eg C8-O2 = 1383(3) Aring and C21-O7 = 1347(4)

Aring] Also the localized C=C bonds in the chromone moeities remain intact after

coordination of the chret chelators as these C=C bonds [C7-C15 = 1414(4) Aring and

C20-C21 = 1411(4) Aring] are shorter than the C-C single bond [C17-C18 = 1537(3) Aring]

that constitutes the bridging ethane moeity

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Fig 2 An ORTEP view of compound 1 showing 50 probability displacement ellipsoids

and the atom labelling The tetrahydrofuran molecules of crystallization were omitted for

clarity

33 Crystal structure of 2

Four molecules of 2 occupies its monoclinic unit cell and each of these

molecules forms dimers with molecules of 2 in adjacent unit cells via classical

hydrogen-bonding interactions [Br1N2A-H2ABr1AN2-H = 257(3) Aring] see Fig

S10 Consequently molecules of 2 are self-assembled in columns aligned with the

[b]-axis Indicative to 1 the constrained bite angle [O1-Re-N1 = 8199(7)ordm] of 2 results

in the deviation of orthogonality in the opposing C17-Re-C19 [8690(1)ordm] bond angle

see Fig 3

The rhenium to halide bonds of 1 [Re1-Br1 = 26455(3) Aring and Re2-Br2 =

26377(3) Aring] and 2 [Re-Br = 26322(8) Aring] are comparable to those found in other facial

tricarbonyl rhenium complexes [26 27] All the remaining coordination bonds of 2

[Re-N1 = 2186(2) Aring Re-O1 = 2141(1) Aring Re-C17 = 1931(2) Aring Re-C18 = 1901(2) Aring

and Re-C19 = 1901(2) Aring] were similar to its chloro-analogue fac-[Re(CO)3(bzch)Cl]

viz Re-Oketone = 2137(2) Aring Re-Nbenzimidazole = 2179(2) Aring and Re-Ccarbonyl = 1929(2) Aring

1904(2) Aring 1898(2) Aring [11] Furthermore the double bond character of the C10-N1

bonds [1336(3) Aring] are clearly established when compared to the C-N bond lengths

[C10-N2 = 1358(3) Aring C16-N1 = 1401(3) Aring and C11-N2 = 1374(3) Aring] In addition the

bridging C9-C10 [1466(3) Aring] bond is single based on the more shorter localized C=C

[1365(3) Aring] chromone bond In turn the degrees of freedom around the C9-10 single

bond allows the chromone and benzimidazole plane to form a dihedral angle of

601ordm Also the benzimidazole and chromone moeities lies out of the plane of the

O1N1C19C17 mean basal plane by 1783ordm and 1837ordm respectively The toluene

molecule of recrystallization from an adjacent unit cell is nearly co-planar with the

bzch chelator of 1 indicating - interactions between this toluene molecule and the

bzch chelator (toluene Csp2 centroid to C9 = 3309 Aring and toluene Csp2 centroid to C10

= 3561 Aring)

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An evaluation of the experimental and optimized geometrical parameters for

the metal complexes reveals that the calculated intraligand bond distances [C17-C18

= 15374 Aring for 1 and C1-C9 = 13601 Aring for 2] and angles [O6-Re2-N3 = 83023ordm for 1

and O1-Re-N1 = 80800ordm for 2] compares well with their analogous experimental

geometrical parameters [C17-C18 = 1537(4) Aring for 1 C1-C9 = 1365(3) Aring for 2 O6-

Re2-N3 = 8393(7)ordm for 1 and O1-Re-N1 = 8199(7)ordm for 2] In addition the differences

in bond lengths found between comparable experimental [eg Re1-C1 = 1942(3) Aring

for 1 and Re-C19 = 1901(2) Aring] and optimized [eg Re1-C1 = 19344 Aring for 1 and Re-

C19 = 19034 Aring for 2] organometallic Re-CO bonds are not significant Discrepencies

found between the experimental [Re1-Br1 = 26455(3) Aring Re2-Br2 = 26377(3) Aring for 1

and Re-Br = 26322(8) Aring for 2] and calculated [Re1-Br1 = 272064 Aring Re2-Br2 = 272059

Aring for 1 and Re-Br = 266556 Aring for 2] rhenium to halide bonds are significant which

are ascribed to the rhenium atoms having lower calculated Natural Population

Analysis charges (0851 for Re12 in 1 and 0889 in 2) than the formal +I charge [28

29] The same trend is observed when examining the Re-Oketonic and Re-N

coordination bonds which were found to be longer in the computational models [eg

Re1-O1 = 21765 Aring Re1-N1 = 22224 Aring for 1 and Re-O1 = 22226 Aring Re-N1 = 23072 Aring

for 2] due to their lower Lewis acidic character of the metal centres than those in the

crystal structures [eg Re1-O1 = 2137(2) Aring Re1-N1 = 2169(2) Aring for 1 and Re-O1 =

2141(2) Aring Re-N1 = 2186(2) Aring for 2]

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Fig 3 An ORTEP view of complex 2 showing 50 probability displacement ellipsoids and

the atom labelling The toluene molecule of crystallization was omitted for clarity

Conclusion

Exploring the coordination behaviours of the diimine chret and chb afforded the di-

and mononuclear rhenium(I) compounds fac-(Re(CO)3Br)2(micro-chret) (1) and fac-

[Re(CO)3(bzch)Br] (2) The interpretation of the IR experimental spectra of the metal

compounds was supported by their simulated spectra calculated at the DFT level of

theory X-ray studies concured with the spectroscopic characterization revealing the

transformation of the chb diimine into the bzch chelator (in 2) and affirming the

coordination modes of the chb (in 1) and bzch (in 2) chelators In addition the 6-

membered chelate rings had a significant influence on the geometrical parameters of

the octahedral geometries of 1 and 2

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Supporting information

CCDC 1451521 and 1451522 contains crystallographic data for this article These data

can be obtained free of charge at wwwccdccamacukcontsretrievinghtml [or

from the Cambridge Crystallographic Data Centre (CCDC) 12 Union Road

Cambridge CB21EZ UK Fax +44(0)1223-336033 Email depositccdccamacuk]

Supplementary figures S1-S10 associated with this article can be found in the online

version

Acknowledgements

We are grateful to the University of KwaZulu-Natal and the National Research

Foundation of South Africa for financial support

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Table 1 Crystal data and structure refinement data

13(C4H8O) 2C7H8

Chemical formula C28H18Br2N4O10Re23(C4H8O) C19H10BrN2O5ReC7H8

Formula weight 131899 70453

TemperatureK 100(2) 100(2)

Crystal system Triclinic Monoclinic

Space group P-1 P21n

Unit cell dimensions (Ǻ deg) a = 128859(6) a = 12400(5)

b = 131199(6) b = 11778(5)

c = 149558(7) c = 16316(5)

α= 114601(2) α = 90000(5)

β = 98138(2) β = 92469(5)

γ = 102350(2) γ = 90000(5)

Crystal size (mm) 013 x 006 x 005 009 x 006 x 005

V(Aring3) 216873 (18) 238007(16)

Z 2 4

Density (calc) (mgm3) 2020 1966

Absorption coefficient (mm-1) 749 682

F(000) 1268 1352

θ range for data collection

(deg)

16 291 20 290

Reflections measured 41497 23824

Observed reflections [Igt2σ(I)] 10414 5621

Independent reflections 11421 6310

DataRestraintsparameters 114210566 56210321

Goodness of fit on F2 103 103

Observed R wR2 0018 0043 0020 0042

Rint 0018 0027

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Table 2 Selected bond lengths [Aring] and bond angles [deg] for 1 The RMSD of 1 is 0720 Aring

Experimental Optimized

Re1-Br1 26455(3) 272064 Re2-Br2 26377(3) 272059 Re1-O1 2137(2) 21765 Re2-O6 2139(2) 21764 Re1-N1 2169(2) 22224 Re2-N3 2171(2) 22224 Re1-C1 1942(3) 19344 Re1-C2 1894(3) 19091 Re1-C3 1897(3) 19071 Re2-C4 1908(3) 19071 Re2-C5 1932(3) 19091 Re2-C6 1893(2) 19343 C16-N1 1286(4) 12919 C19-N3 1291(4) 12919 C14-O1 1259(4) 12502 C28-O6 1261(3) 12503 C1-O3 1144(3) 11492 C8-O2 1383(3) 13796 C21-O7 1347(4) 13440 C7-C15 1414(4) 14102 C20-C21 1411(4) 14103 C17-C18 1537(3) 15374 O1-Re1-N1 8452(7) 83027 O6-Re2-N3 8393(7) 83023 C2-Re1-Br1 17685(8) 177228 O1-Re1-C3 17741(9) 176550 C1-Re1-N1 1762(1) 174310 Br2-Re2-C6 17699(8) 177236 C4-Re2-O6 17641(9) 176545 N3-Re2-C5 1742(1) 174309 C16-N1-C17 1150(2) 114920 C18-N3-C19 1148(2) 114920

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Table 3 Selected bond lengths [Aring] and bond angles [deg] for 2 The RMSD of 2 is 0267 Aring

Experimental Optimized

Re-Br 26322(8) 266556 Re-N1 2186(2) 23072 Re-O1 2141(2) 22226 Re-C17 1931(2) 19263 Re-C18 1901(2) 19150 Re-C19 1901(2) 19034 C9-C10 1466(3) 14608 C1-C9 1365(3) 13601 O1-Re-N1 8199(7) 80800 C17-Re-C19 8690(1) 88380 Br-Re-C18 17582(7) 176266

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References

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rhenium Chem Soc Rev 27 (1998) 43-55

[2] S Jurisson D Berning J Wei M Dangshe Coordination compounds in

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[3] S Juumlrgens WA Herrmann FE Kuumlhn Rhenium and technetium based

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[4] U Abram R Alberto Technetium and Rhenium - Coordination Chemistry and

Nuclear Medical Applications Braz Chem Soc 17 (2006) 1486-1500

[5] SL Binkley TC Leeper RS Rowlett RS Herrick CJ Ziegler

Re(CO)3(H2O)3+ binding to lysozyme structure and reactivity Mettalomics 3

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[6] RS Herrick TJ Brunker C Maus K Crandall A Cetin CJ

Ziegler Aqueous preparation and physiological stability studies of

Re(CO)3(tripodal) compounds Chem Commun (2006) 4330-4331

[7] K Potgieter P Mayer TIA Gerber IN Booysen Coordination behaviour of

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towards the fac-[Re(CO)3]+ and [ReO]3+ cores Polyhedron 28 (2009) 2808-2812

[8] CL Ferreira CB Ewart SR Bayly B O Patrick J Steele MJ Adam C

Orvig Glucosamine Conjugates of Tricarbonylcyclopentadienyl Rhenium(I)

and Technetium(I) Cores Inorg Chem 45 (2006) 6979-6987

[9] Q Nadeem D Can Y Shen M Felber Z Mahmooda R Alberto Synthesis of

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as radiopharmaceutical probes Org Biomol Chem 12 (2014) 1966-1974

[10] IN Booysen M Ismail TIA Gerber M Akerman B Van Brecht Oxo and

oxofree rhenium(V) complexes with NO-donor Schiff bases S Afr J Chem 65

(2012) 174-177

[11] IN Booysen MB Ismail OQ Munro Mono- and dinuclear rhenium(I)

compounds with bidentate benzimidazole chelators Inorg Chem Commun 30

(2013) 168-172

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[12] IN Booysen MB Ismail MP Akerman Coordination behaviour of chromone

Schiff bases towards the [ReVO]3+ and [ReI(CO)3]+ cores J Coord Chem 66

(2013) 4371-4386

[13] S Bhatnagar S Sahir P Kackar S Kaushik MK Dave A Shukla A Goel

Synthesis and docking studies on styryl chromones exhibiting cytotoxicity in

human breast cancer cell line Bioorg Med Chem Lett 20 (2010) 4945-4950

[14] M Recanatini A Bisi A Cavalli F Belluti S Gobbi A Rampa P Valenti M

Palzer A Palusczak RW Hartmann A New Class of Nonsteroidal Aromatase

Inhibitorsthinsp Design and Synthesis of Chromone and Xanthone Derivatives and

Inhibition of the P450 Enzymes Aromatase and 17α-HydroxylaseC1720-

Lyase J Med Chem 44 (2001) 672-680

[15] IN Booysen A Adebisi MP Akerman OQ Munro B Xulu Coordination of

di- and triimine ligands at ruthenium(II) and ruthenium(III) centers structural

electrochemical and radical scavenging studies J Coord Chem (2016) doi

1010800095897220161177177

[16] Bruker APEX2 SAINT and SADABS Bruker AXS Inc (2010) Madison

Wisconsin USA

[17] RH Blessing An empirical correction for absorption anisotropy Acta Cryst

A51 (1995) 33-38

[18] GM Sheldrick A short history of SHELX Acta Cryst A64 (2008) 112-122

[19] LJ Farrugia WinGX and ORTEP for Windows an update J Appl Cryst 45

(2012) 849-854

[20] MJ Frisch GW Trucks HB Schlegel GE Scuseria MA Robb JR

Cheeseman G Scalmani V Barone B Mennucci GA Petersson H Nakatsuji

M Caricato X Li HP Hratchian AF Izmaylov J Bloino G Zheng JL

Sonnenberg M Hada M Ehara K Toyota R Fukuda J Hasegawa M Ishida

T Nakajima Y Honda O Kitao H Nakai T Vreven JA Montgomery Jr JE

Peralta F Ogliaro M Bearpark JJ Heyd E Brothers KN Kudin VN

Staroverov R Kobayashi J Normand K Raghavachari A Rendell JC

Burant SS Iyengar J Tomasi M Cossi N Rega JM Millam M Klene JE

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Knox JB Cross V Bakken C Adamo J Jaramillo R Gomperts RE

Stratmann O Yazyev AJ Austin R Cammi C Pomelli JW Ochterski RL

Martin K Morokuma VG Zakrzewski GA Voth P Salvador JJ

Dannenberg S Dapprich AD Daniels O Farkas JB Foresman JV Ortiz J

Cioslowski DJ Fox GAUSSIAN 09 (Revision A01) Gaussian

IncWallingford CT (2009)

[21] A Brink HG Visser A Roodt Novel imino rhenium(I) tricarbonyl complexes

of salicylidene-derived ligands Synthesis X-ray crystallographic studies

spectroscopic characterization and DFT calculations Polyhedron 52 (2013) 416-

423

[22] J Mukiza TIA Gerber EC Hosten Decarboxylation of 5-amino-orotic acid

and a Schiff base derivative by rhenium(V) Inorg Chem Comm 57 (2015) 54-

57

[23] K Potgieter P Mayer T Gerber N Yumata E Hosten I Booysen R Betz M

Ismail B van Brecht Rhenium(I) tricarbonyl complexes with multidentate

nitrogen-donor derivatives Polyhedron 49 (2013) 67-73

[24] IN Booysen I Ebinumoliseh MP Akerman B Xulu A rhenium(I) compound

bearing a dimerized chromone NO bidentate chelator Inorg Chem Comm 62

(2015) 8-10

[25] P Mayer TIA Gerber B Buyambo A Abrahams Coordination behaviour of

acetylacetone-derived Schiff bases towards rhenium(I) and (V) Polyhedron 28

(2009) 1174-1178

[26] T Jurca O Ramadan I Korobkov DS Richeson Employing sterically

encumbered bis(imino)pyridine ligands in support of fac-rhenium(I) carbonyls

J Organomet Chem 802 (2016) 27-31

[27] J Ho WY Lee KJT Koh PPF Lee YK Yan Rhenium(I) tricarbonyl

complexes of salicylaldehyde semicarbazones Synthesis crystal structures and

cytotoxicity J Inorg Biochem 119 (2013) 10-20

[28] B Machura A Świtlicka M Wolff J Kusz R Kruszynski Mono- and di-

nuclear oxorhenium(V) complexes of 47-diphenyl-110-phenanthroline

Polyhedron 28 (2009) 3999-4009

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[29] B Machura M Jaworska P Lodowski Natural bond orbital analysis and

density functional study of linear and bent oxo-bridged dimers of rhenium(V)

J Mol Struc-Theochem 766 (2006) 1-8

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Highlights

bull Chromone rhenium(I) compounds

bull Simulated IR spectra

bull Low calculated RMSDs

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Formation characterization and computational studies of

mono- and dinuclear Rhenium(I) Chromone compounds

Ifeoma Ebinumoliseh a Irvin Noel Booysen a Matthew Piers Akermana Bheki

Xulua

a School of Chemistry and Physics University of KwaZulu-Natal Private Bag X01 Scottsville 3209

Pietermaritzburg South Africa

Abstract

Herein we report the formation and characterization of a novel dinuclear rhenium(I)

compound fac-(Re(CO)3Br)2(micro-chret) (1) [chret = N Nlsquo-bis(2-amino-3-

imino)methylenechromone-12-ethane] and a mononuclear metal complex fac-

[Re(CO)3(bzch)Br] (2) [bzch = 2-benzimidazole-4H-chromen-4-one] The metal

complexes were characterized by 1H NMR- IR- UV-Vis melting point and

conductivity measurements The solid-state structures for 1 and 2 were confirmed

via single crystal X-ray analysis X-ray studies of 2 revealed the transformation of the

chb diimine into the bzch chelator (in 2) The simulated IR spectra for the respective

metal complexes provided insight in the interpretation of their corresponding

experimental spectra

Keywords Rhenium Chromone Spectral Characterization DFT Studies Crystal

structure

Corresponding author Booyseniukznacza

1 Introduction

The considerable attention received by the coordination chemistry of rhenium

stems from the ideal properties of its 186- and 188-radionuclides which are well

suited for radiotherapy [1-3] For example the bone-targeting therapeutic

radiopharmaceutical rhenium-HEDP (HEDP = hydroxyethylidene disphosphonate)

has several advantages over the commercially available alternatives in terms of

efficacy safety and the ability to be produced on site allowing for the rapid

treatment of patients with painful bone metastases [4] Furthermore the facial

tricarbonylrhenium(I) core has shown to serve as an ideal synthon for the

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formulation of new rhenium radiopharmaceuticals This is illustrated by the facial

tricarbonylrhenium(I) complexes stability under physiological conditions where the

small size of the fac-[Re(CO)3]+ core allows binding to various biological entities [5-

6] However the next generation of potential rhenium radiopharmaceuticals requires

chelators which can stabilize the metal centre both in the low and high oxidation

states [7] Furthermore these multidentate chelators should also cater for the

inclusion of biologically active moieties which may aid in the target specific

biodistribution of the metallopharmaceuticals [8 9]

In our previous studies we have reported the isolation of oxorhenium(V) and

facial tricarbonylrhenium(I) complexes with Schiff bases encompassing uracil

chromone or benz(othiazoleimidazole) moieties [10-12] These multidentate Schiff

base chelators illustrated diverse coordination behaviours leading to mono- or

dinuclear rhenium compounds For example an unique dinuclear rhenium(I)

complex (micro-bzp)2[Re(CO)3]2 [Hbzp = N-(2-hydroxybenzylidene)-benzimidazole] has

a centralized 8-membered chelate ring formed by coordination of the benzimidazole

nitrogens to the individual rhenium atoms [11] Furthermore different

transformations of the chromone mono-imines 2-(2-thiolphenyliminomethyl)-4H-

chromen-4-one (Htch) and H3uch [5-((4-hydroxy-2-methoxy-2H-chromen-3-

yl)methyleneamino)-6-amino-13-dimethylpyrimidine-24(1H 3H)-dione] were

observed upon their coordination reactions with trans-[ReOBr3(PPh3)3] to afford

[ReO(Hns)] H2ns = bis-[(2-phenylthiolate)iminomethyl]-methyl-1-(2-

hydroxyphenyl)prop-2-en-1-one and [ReO(OCH3)(PPh3)(Huch)] [12]

As a continuation of our research studies on rhenium herein we consider the

coordination behaviours of multidentate diimines encompassing chromone moieties

This secondary metabolite chromone and its derivatives are known to induce

cytotoxic effects in breast cancer cell lines [13 14] Hence we report the coordination

reactions of [Re(CO)5Br] with the diimines N Nlsquo-bis(2-amino-3-

imino)methylenechromone-12-ethane (chret) and NNrsquo-bis((3-chromone)methylene)-

benzene-12-diamine (chb) to afford a novel dinuclear rhenium(I) compound fac-

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(Re(CO)3Br)2(micro-chret) (1) and a mononuclear compound fac-[Re(CO)3(bzch)Br] (2)

[bzch = 2-benzimidazole-4H-chromen-4-one]

N NO

O

O

Ochb

N NO

O

O

O

chret

NH2 H2N

N

HNO

O

bzch

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2 Experimental

21 Materials and methods

The reagents bromopentacarbonylrhenium(I) ethylenediamine

12-diaminobenzene 2-amino-3-formylchromone and 3-formylchromone were

obtained from Sigma Aldrich and used as received All solvents and common salts

were obtained from Merck SA Reagent grade toluene was dried over sodium wire

solvents were used without further purification The synthetic procedure and

characterization data for the free-ligand chret can be found in the online supporting

information document see Figs S1 S2 and S5 The diimine chb was obtained from

the condensation reaction of 12-diaminobenzene with a two-fold molar quantity of

3-formylchromone [15]

The infrared spectra were recorded on a Perkin-Elmer 100 spectrometer in the

4000 ndash 450 cm-1 range The 1H NMR spectra were obtained using a Bruker Avance

400 MHz spectrometer All NMR spectra were recorded in deuterated

dimethylsulphoxide UV-Vis spectra were recorded using a Perkin Elmer Lambda

25 The extinction coefficients (ε) are given in dm3mol-1cm-1 Melting points were

determined using a Stuart SMP3 melting point apparatus The conductivity

measurements were determined at 295K on a Radiometer R21M127CDM 230

conductivity and pH meter

22 fac-(Re(CO)3Br)2(micro-chret) (1)

A 11 molar reaction mixture of [Re(CO)5Br] (0050 g 0123 mmol) and chret (0049 g

0123 mmol) in 15 cm3 of anhydrous toluene was heated at reflux under nitrogen for

4 hrs The resultant reaction mixture was cooled to room temperature and filtered

An orange precipitate was dried under vacuum Pale orange X-ray quality

crystalline parallelograms were obtained from layering the precipitate with a 11

(vv) THFhexane over a period of five days MP = 215 - 220 ᴼC yield = 87

Conductivity (DMSO 10-3M) 1693 ohmcm2mol-1 IR (νmaxcm-1) ν(N-H) 2920 2850

(m) ν(CequivO) 2015 1871 (vs) ν(C=O) 1655 (s) ν(C=N) 1615 1613 (s) ν(O-C-O) 1464

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cm-1 (s) 1H NMR (295 K ppm) 1091 (br s 4H 2x NH2) 895 ndash 865 (m 6H H10

H12 H16 H19 H24 H26) 812 ndash 711 (m 4H H9 H11 H23 H25) 469 ndash 439 (m 4H

H17 H17rsquo H18 H18rsquo) UV-Vis (DMSO λmax(K M-1cm-1)) 269 nm (24159) 296 nm (sh

20140) 405 nm (sh 2464)

23 fac-[Re(CO)3(bzch)Br] (2)

The equimolar coordination reaction between [Re(CO)5Br] (0050 g 0123 mmol) and

chb (0052 g 0123 mmol) was conducted in 15 cm3 of anhydrous toluene heated at

reflux under nitrogen for 4 hrs The resultant reaction mixture was cooled to room

temperature and an orange precipitate was filtered and dried under vacuum Pale

orange cubic crystals suitable for X-ray analysis were obtained from dissolving the

precipitate in tetrahydrofuran and layering with hexane MP = 210 ndash 211 ᴼC yield =

93 Conductivity (DMSO 10-3M) 2372 ohmcm2mol-1 IR (νmaxcm-1) ν(N-H) 2915

(w) ν(CequivO) 2015 1871 (vs) ν(C=O) 1628 1607 (s) ν(C=N) 1567 (s) ν(O-C-O) 1461 (s) 1H NMR (295 K ppm) 969 (s 1H H1) 939 (s 1H NH) 827-722 (m 8H H3 H4

H5 H6 H12 H13 H14 H15) UV-Vis (DMSO λmax(K M-1cm-1)) 275 nm (sh 26107)

282 nm (27295) 309 nm (sh 22025) 394 nm (6614) 418 nm (sh 4394)

24 X-ray diffraction

The X-ray data for C28H18Br2N4O10Re23(C4H8O) and C19H10BrN2O5ReC7H8 were

recorded on a Bruker Apex Duo equipped with an Oxford Instruments Cryojet

operating at 100(2) K and an Incoatec microsource operating at 30W power Crystal

and structure refinement data are given in Table 1 Selected bond lengths and

angles are given in Tables 2 and 3 In both cases the data were collected with Mo Kα

(λ = 071073 Aring) radiation at a crystal-to-detector distance of 50 mm The following

conditions were used for data collection omega and phi scans with exposures taken

at 30 W X-ray power and 050ordm frame widths using APEX2 [16] The data were

reduced with the program SAINT [16] using outlier rejection scan speed scaling as

well as standard Lorentz and polarization correction factors A SADABS semi-

empirical multi-scan absorption correction [17] was applied to the data Direct

methods SHELX-2014 [18] and WinGX [19] were used to solve both structures All

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non-hydrogen atoms were located in the difference density map and refined

anisotropically with SHELX-2014 [20] All hydrogen atoms were included as

idealised contributors in the least squares process Their positions were calculated

using a standard riding model with C-Haromatic distances of 093 Aring and Uiso = 12 Ueq

C-Hmethylene distances of 099 Aring and Uiso = 12 Ueq and CndashHmethyl distances of 098 Aring and

Uiso = 15 Ueq The amine hydrogen atoms were located in the difference density

map and allowed to refine isotropically

25 Computational details

Molecular simulations were conducted with GAUSSIAN 09W [20] Geometry

optimizations of 1 and 2 were achieved through a DFT calculation using the B3LYP

functional with an accompanying hybrid basis set viz the 6-311G++ (d p) basis set

was applied to all the C H N O and Br and the LANL2DZ basis set which makes

use of effective core potentials applied to the metal centre [12] Prior to the

calculation the solvent molecules of recrystallization for the respective metal

complexes were omitted from their crystal structures and the resultant structures

were used as the starting conformers Good agreement was found between the

optimized and experimental geometrical parameters (refer to Tables 2 and 3) with

the minor deviations attributed to the fact that the gas phase optimized structures do

not account for intermolecular interactions or any short distance contacts The close

correlation between the optimized and geometrical parameters of the respective

complexes is further emphasized by the low calculated root-mean-square deviation

(RMSD) see Fig 1 The larger RMSD of 1 is mainly ascribed to the largely free

rotation of the C-C single bonds within the chret chelator Using the optimized

structure of the metal complex the lack of any negative Eigen values in the

frequency calculations confirmed that the structures are at global minima on their

individual potential energy surfaces [21]

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Fig 1 Overlay structures of the optimized and experimental crystal structures for the

respective complexes with their corresponding RMSD values The crystal structures are

shown in yellow while the optimized structures are given in blue

3 Results and Discussion

31 Synthesis spectral characterization and computational studies

The metallic compounds fac-(Re(CO)3Br)2(micro-chret) (1) and fac-

[Re(CO)3(bzch)Br] (2) [bzch = 2-benzimidazole-4H-chromen-4-one] were synthesized

under anaerobic conditions from the equimolar reaction of [Re(CO)5Br] with the

diimines chret and chb respectively In 1 the chret ligand bridges two fac-

[Re(CO)3Br] units while coordinating as a bidentate moiety to each metal centre via

its NiminoOketo donor sets Despite the use of anaerobic conditions X-ray studies of 2

revealed that the chb diimine underwent intraligand cyclization followed by the

hydrolysis of one of its imine bonds In fact the chloro rhenium(I) analogue fac-

[Re(CO)3(bzch)Cl] was similarly formed from the reaction of [Re(CO)5Cl] with the

Schiff base ligand 2-(2- aminophenyliminomethyl)-4H-chromen-4-one (H2pch) which

led to the transformation of the latter to a bzch moiety [11] However no

transformation of the diimine chb occured in the dinuclear ruthenium(III)

compound (micro-chb)[mer-RuCl3(PPh3)]2 where the neutral chb moiety bridges the two

cis-[RuIIICl3] cores via its ketonic oxygen and imino nitrogen atoms [15] In contrast

to 2rsquos centralized 1 2-((methylene)imino)-benzene moiety the flexible

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((imino)methylene)-12-ethane bridging moiety of 1 minimizes steric strain within its

chret chelator which effectively induces stability and prevents the transformation of

the chret ligand Furthermore compounds 1 and 2 exhibits good solubility in high

boiling point polar solvents including dimethylsulfoxide and dimethylformamide

while showing a relatively modest solubility in tetrahydrofuran and poor solubility

in chlorinated solvents such as chloroform The low molar conductivities [ΛM = 1693

and 2372 ohmcm2mol-1] of the metallic compounds indicates their neutrality in

DMSO

Broad vibrational bands are observed below 1700 cm-1 in the experimental IR

spectra of the metal complexes which could not be clearly assigned without the aid

of the simulated IR spectra of 1 and 2 see Figs S1 ndash S4 Both the experimental [2015

1871 cm-1 for 1 and 2] and simulated [2105 2018 2016 cm-1 for 1 and 2097 2017 1993

cm-1 for 2] IR spectra are dominated by the intense stretches of the carbonyl co-

ligands Similarly the ν(N-H) vibrations of 1 and 2 appear as weak intensity

vibrational bands in their respective simulated [3644 cm-1 for 1 and 3654 3289 cm-1

for 2] and experimental [2920 2850 cm-1 for 1 and 2915 cm-1 for 2] IR spectra The

simulated IR spectrum of 1 indicates distinctive vibrational bands associated with

the ketonic (at 1687 cm-1) imine (at 1567 cm-1) and ether (at 1469 cm-1) bonds

whereas the corresponding IR stretching frequencies can be found at 1655 cm-1 [for

ν(C=O)] 1464 cm-1 1615 [for ν(O-C-O)] and 1613 cm-1 [for ν(C=N)] in the

experimental IR spectrum of 1 Correlating the simulated IR spectrum of 2 with its

experimental IR spectrum revealed that the experimental vibrations for ν(C=O) are

found at 1628 and 1607 cm-1 while ν(C=N) and ν(O-C-O) appears at 1567 cm-1 and

1461 cm-1 respectively

In the proton NMR spectrum of 1 the aliphatic protons of the bridging ethane

moiety resonates as a multiplet between 469 and 439 ppm see Fig S6 A broad

singlet at 1091 ppm corresponds to the protons of the amino nitrogens of 1 but the

analogous protons were observed as two broad signals in the proton NMR spectrum

of the free-ligand chret see Fig S5 For 1 the aromatic protons of the chromone

moieties and the imino signal coalesce into two multiplets (viz 895 ndash 865 ppm and

812 ndash 711 ppm) in comparison to the corresponding well-resolved signals at 872

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ppm (for the imino protons) and 798 767 737 ppm (for the aromatic protons of the

chromone moieties) of the free-ligand chret The most intense signal in the 1H NMR

spectrum of 2 is due to the H1 proton positioned on the chromone moiety which

appears as a sharp singlet (at 969 ppm)

The benzimidazole proton in 2 resonates as an intense signal at 939 ppm

which integrates to one while the multiplet between 827 and 722 ppm are due to

the remaining aromatic peaks The presence of the pi-conjugated neutral chelators in

1 and 2 results in the occurrence of only intra-ligand - transitions in their UV-Vis

spectra see Figs S7 and S8 As expected no metal-based d-d transitions are

observed at more red-shifted regions due to the low-spin d6 electron configurations

of 1 and 2

32 Crystal structure of 1

Compound 1 co-crystallized with three tetrahydrofuran molecules of

recrystallization in its triclinic unit cell The crystal lattice of 1 is stabilized by a

network of classical intramolecular [Br1H4a-N4 = 273(4) Aring and Br2H2a-N2 =

260(4) Aring] and intermolecular hydrogen bonding [O11AH2b-N2 = 195(4) Aring and

O11BH4b-N4 = 191(5) Aring] see Fig S9 Collectively these hydrogen bonding

interactions allows molecules of 1 to pack in columns parallel to the [a]- and [b]-axes

The metal centres of 1 are positioned in the centre of the distorted

octahedrons which are largely imposed on by their constrained bite angles [O1-Re1-

N1 = 8452(7)ordm and N3-Re2-O6 = 8393(7)ordm] see Fig 2 Consequently the C2-Re1-Br1

[17685(8)ordm] O1-Re1-C3 [17741(9)ordm] C1-Re1-N1 [1762(1)ordm] Br2-Re2-C6 [17699(8)ordm]

C4-Re2-O6 [17641(9)ordm] and N3-Re2-C5 [1742(1)ordm] deviate all from linearity The

flexibility of the bridging ethane moiety affords narrower C=N-C [C18-N3-C19 =

1148(2)ordm and C16-N1-C17 = 1150(2)ordm] bond angles than the expected 120ordm for a bond

angle containing a central sp2 hybridized nitrogen Despite the influence of the

bridging ethane moiety the imino bonds [C16-N1 = 1286(4) Aring and C19-N3 =

1291(4) Aring] of 1 are in the range [1285(3) - 1312(6) Aring] observed for similar bonds

found in other Schiff bases [7 11 21 22 23] Across the respective octahedrons only

the Re1-C2 [1894(3) Aring] and Re2-C6 [1893(3) Aring] bonds are nearly equidistant which

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reflects similar trans-influence induced by the Br1 and Br2 atoms respectively

Hence the comparable cis-orientated organometallic bonds [Re1-C1 = 1942(3) Aring

Re1-C3 = 1897(3) Aring Re2-C4 = 1908(3) Aring and Re2-C5 = 1932(3) Aring] across the

octahedrons in 1 differs

The rhenium to ketonic [Re1-O1 = 2137(2) Aring and Re2-O6 = 2139(2) Aring] and

imino nitrogen [Re1-N1 = 2169(2) Aring and Re2-N3 = 2171(2) Aring] bonds are similar to

analogous bonds found within fac-[Re(CO)3(chrpychr)Br] (chrpychr = 2-(4-oxo-4H-

chromen-3-yl)-5H-chromeno[23-d]pyrimidin-5-one) and [(micro-O)ReOCl(amp)2]

(amp= 6-amino-3-methyl-1-phenyl-4-azahept-2-ene-1-one) [24 25] Bond orders with

the chret chelator is established based on the ketonic bonds [C14-O1 = 1259(4) Aring and

C28-O6 = 1261(3) Aring] being longer than the carbonyl bonds [eg C1-O3 = 1144(3) Aring]

but yet shorter than the ether bonds [eg C8-O2 = 1383(3) Aring and C21-O7 = 1347(4)

Aring] Also the localized C=C bonds in the chromone moeities remain intact after

coordination of the chret chelators as these C=C bonds [C7-C15 = 1414(4) Aring and

C20-C21 = 1411(4) Aring] are shorter than the C-C single bond [C17-C18 = 1537(3) Aring]

that constitutes the bridging ethane moeity

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Fig 2 An ORTEP view of compound 1 showing 50 probability displacement ellipsoids

and the atom labelling The tetrahydrofuran molecules of crystallization were omitted for

clarity

33 Crystal structure of 2

Four molecules of 2 occupies its monoclinic unit cell and each of these

molecules forms dimers with molecules of 2 in adjacent unit cells via classical

hydrogen-bonding interactions [Br1N2A-H2ABr1AN2-H = 257(3) Aring] see Fig

S10 Consequently molecules of 2 are self-assembled in columns aligned with the

[b]-axis Indicative to 1 the constrained bite angle [O1-Re-N1 = 8199(7)ordm] of 2 results

in the deviation of orthogonality in the opposing C17-Re-C19 [8690(1)ordm] bond angle

see Fig 3

The rhenium to halide bonds of 1 [Re1-Br1 = 26455(3) Aring and Re2-Br2 =

26377(3) Aring] and 2 [Re-Br = 26322(8) Aring] are comparable to those found in other facial

tricarbonyl rhenium complexes [26 27] All the remaining coordination bonds of 2

[Re-N1 = 2186(2) Aring Re-O1 = 2141(1) Aring Re-C17 = 1931(2) Aring Re-C18 = 1901(2) Aring

and Re-C19 = 1901(2) Aring] were similar to its chloro-analogue fac-[Re(CO)3(bzch)Cl]

viz Re-Oketone = 2137(2) Aring Re-Nbenzimidazole = 2179(2) Aring and Re-Ccarbonyl = 1929(2) Aring

1904(2) Aring 1898(2) Aring [11] Furthermore the double bond character of the C10-N1

bonds [1336(3) Aring] are clearly established when compared to the C-N bond lengths

[C10-N2 = 1358(3) Aring C16-N1 = 1401(3) Aring and C11-N2 = 1374(3) Aring] In addition the

bridging C9-C10 [1466(3) Aring] bond is single based on the more shorter localized C=C

[1365(3) Aring] chromone bond In turn the degrees of freedom around the C9-10 single

bond allows the chromone and benzimidazole plane to form a dihedral angle of

601ordm Also the benzimidazole and chromone moeities lies out of the plane of the

O1N1C19C17 mean basal plane by 1783ordm and 1837ordm respectively The toluene

molecule of recrystallization from an adjacent unit cell is nearly co-planar with the

bzch chelator of 1 indicating - interactions between this toluene molecule and the

bzch chelator (toluene Csp2 centroid to C9 = 3309 Aring and toluene Csp2 centroid to C10

= 3561 Aring)

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An evaluation of the experimental and optimized geometrical parameters for

the metal complexes reveals that the calculated intraligand bond distances [C17-C18

= 15374 Aring for 1 and C1-C9 = 13601 Aring for 2] and angles [O6-Re2-N3 = 83023ordm for 1

and O1-Re-N1 = 80800ordm for 2] compares well with their analogous experimental

geometrical parameters [C17-C18 = 1537(4) Aring for 1 C1-C9 = 1365(3) Aring for 2 O6-

Re2-N3 = 8393(7)ordm for 1 and O1-Re-N1 = 8199(7)ordm for 2] In addition the differences

in bond lengths found between comparable experimental [eg Re1-C1 = 1942(3) Aring

for 1 and Re-C19 = 1901(2) Aring] and optimized [eg Re1-C1 = 19344 Aring for 1 and Re-

C19 = 19034 Aring for 2] organometallic Re-CO bonds are not significant Discrepencies

found between the experimental [Re1-Br1 = 26455(3) Aring Re2-Br2 = 26377(3) Aring for 1

and Re-Br = 26322(8) Aring for 2] and calculated [Re1-Br1 = 272064 Aring Re2-Br2 = 272059

Aring for 1 and Re-Br = 266556 Aring for 2] rhenium to halide bonds are significant which

are ascribed to the rhenium atoms having lower calculated Natural Population

Analysis charges (0851 for Re12 in 1 and 0889 in 2) than the formal +I charge [28

29] The same trend is observed when examining the Re-Oketonic and Re-N

coordination bonds which were found to be longer in the computational models [eg

Re1-O1 = 21765 Aring Re1-N1 = 22224 Aring for 1 and Re-O1 = 22226 Aring Re-N1 = 23072 Aring

for 2] due to their lower Lewis acidic character of the metal centres than those in the

crystal structures [eg Re1-O1 = 2137(2) Aring Re1-N1 = 2169(2) Aring for 1 and Re-O1 =

2141(2) Aring Re-N1 = 2186(2) Aring for 2]

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Fig 3 An ORTEP view of complex 2 showing 50 probability displacement ellipsoids and

the atom labelling The toluene molecule of crystallization was omitted for clarity

Conclusion

Exploring the coordination behaviours of the diimine chret and chb afforded the di-

and mononuclear rhenium(I) compounds fac-(Re(CO)3Br)2(micro-chret) (1) and fac-

[Re(CO)3(bzch)Br] (2) The interpretation of the IR experimental spectra of the metal

compounds was supported by their simulated spectra calculated at the DFT level of

theory X-ray studies concured with the spectroscopic characterization revealing the

transformation of the chb diimine into the bzch chelator (in 2) and affirming the

coordination modes of the chb (in 1) and bzch (in 2) chelators In addition the 6-

membered chelate rings had a significant influence on the geometrical parameters of

the octahedral geometries of 1 and 2

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Supporting information

CCDC 1451521 and 1451522 contains crystallographic data for this article These data

can be obtained free of charge at wwwccdccamacukcontsretrievinghtml [or

from the Cambridge Crystallographic Data Centre (CCDC) 12 Union Road

Cambridge CB21EZ UK Fax +44(0)1223-336033 Email depositccdccamacuk]

Supplementary figures S1-S10 associated with this article can be found in the online

version

Acknowledgements

We are grateful to the University of KwaZulu-Natal and the National Research

Foundation of South Africa for financial support

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Table 1 Crystal data and structure refinement data

13(C4H8O) 2C7H8

Chemical formula C28H18Br2N4O10Re23(C4H8O) C19H10BrN2O5ReC7H8

Formula weight 131899 70453

TemperatureK 100(2) 100(2)

Crystal system Triclinic Monoclinic

Space group P-1 P21n

Unit cell dimensions (Ǻ deg) a = 128859(6) a = 12400(5)

b = 131199(6) b = 11778(5)

c = 149558(7) c = 16316(5)

α= 114601(2) α = 90000(5)

β = 98138(2) β = 92469(5)

γ = 102350(2) γ = 90000(5)

Crystal size (mm) 013 x 006 x 005 009 x 006 x 005

V(Aring3) 216873 (18) 238007(16)

Z 2 4

Density (calc) (mgm3) 2020 1966

Absorption coefficient (mm-1) 749 682

F(000) 1268 1352

θ range for data collection

(deg)

16 291 20 290

Reflections measured 41497 23824

Observed reflections [Igt2σ(I)] 10414 5621

Independent reflections 11421 6310

DataRestraintsparameters 114210566 56210321

Goodness of fit on F2 103 103

Observed R wR2 0018 0043 0020 0042

Rint 0018 0027

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Table 2 Selected bond lengths [Aring] and bond angles [deg] for 1 The RMSD of 1 is 0720 Aring

Experimental Optimized

Re1-Br1 26455(3) 272064 Re2-Br2 26377(3) 272059 Re1-O1 2137(2) 21765 Re2-O6 2139(2) 21764 Re1-N1 2169(2) 22224 Re2-N3 2171(2) 22224 Re1-C1 1942(3) 19344 Re1-C2 1894(3) 19091 Re1-C3 1897(3) 19071 Re2-C4 1908(3) 19071 Re2-C5 1932(3) 19091 Re2-C6 1893(2) 19343 C16-N1 1286(4) 12919 C19-N3 1291(4) 12919 C14-O1 1259(4) 12502 C28-O6 1261(3) 12503 C1-O3 1144(3) 11492 C8-O2 1383(3) 13796 C21-O7 1347(4) 13440 C7-C15 1414(4) 14102 C20-C21 1411(4) 14103 C17-C18 1537(3) 15374 O1-Re1-N1 8452(7) 83027 O6-Re2-N3 8393(7) 83023 C2-Re1-Br1 17685(8) 177228 O1-Re1-C3 17741(9) 176550 C1-Re1-N1 1762(1) 174310 Br2-Re2-C6 17699(8) 177236 C4-Re2-O6 17641(9) 176545 N3-Re2-C5 1742(1) 174309 C16-N1-C17 1150(2) 114920 C18-N3-C19 1148(2) 114920

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Table 3 Selected bond lengths [Aring] and bond angles [deg] for 2 The RMSD of 2 is 0267 Aring

Experimental Optimized

Re-Br 26322(8) 266556 Re-N1 2186(2) 23072 Re-O1 2141(2) 22226 Re-C17 1931(2) 19263 Re-C18 1901(2) 19150 Re-C19 1901(2) 19034 C9-C10 1466(3) 14608 C1-C9 1365(3) 13601 O1-Re-N1 8199(7) 80800 C17-Re-C19 8690(1) 88380 Br-Re-C18 17582(7) 176266

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[12] IN Booysen MB Ismail MP Akerman Coordination behaviour of chromone

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[13] S Bhatnagar S Sahir P Kackar S Kaushik MK Dave A Shukla A Goel

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[15] IN Booysen A Adebisi MP Akerman OQ Munro B Xulu Coordination of

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[18] GM Sheldrick A short history of SHELX Acta Cryst A64 (2008) 112-122

[19] LJ Farrugia WinGX and ORTEP for Windows an update J Appl Cryst 45

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[20] MJ Frisch GW Trucks HB Schlegel GE Scuseria MA Robb JR

Cheeseman G Scalmani V Barone B Mennucci GA Petersson H Nakatsuji

M Caricato X Li HP Hratchian AF Izmaylov J Bloino G Zheng JL

Sonnenberg M Hada M Ehara K Toyota R Fukuda J Hasegawa M Ishida

T Nakajima Y Honda O Kitao H Nakai T Vreven JA Montgomery Jr JE

Peralta F Ogliaro M Bearpark JJ Heyd E Brothers KN Kudin VN

Staroverov R Kobayashi J Normand K Raghavachari A Rendell JC

Burant SS Iyengar J Tomasi M Cossi N Rega JM Millam M Klene JE

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Knox JB Cross V Bakken C Adamo J Jaramillo R Gomperts RE

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Martin K Morokuma VG Zakrzewski GA Voth P Salvador JJ

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[21] A Brink HG Visser A Roodt Novel imino rhenium(I) tricarbonyl complexes

of salicylidene-derived ligands Synthesis X-ray crystallographic studies

spectroscopic characterization and DFT calculations Polyhedron 52 (2013) 416-

423

[22] J Mukiza TIA Gerber EC Hosten Decarboxylation of 5-amino-orotic acid

and a Schiff base derivative by rhenium(V) Inorg Chem Comm 57 (2015) 54-

57

[23] K Potgieter P Mayer T Gerber N Yumata E Hosten I Booysen R Betz M

Ismail B van Brecht Rhenium(I) tricarbonyl complexes with multidentate

nitrogen-donor derivatives Polyhedron 49 (2013) 67-73

[24] IN Booysen I Ebinumoliseh MP Akerman B Xulu A rhenium(I) compound

bearing a dimerized chromone NO bidentate chelator Inorg Chem Comm 62

(2015) 8-10

[25] P Mayer TIA Gerber B Buyambo A Abrahams Coordination behaviour of

acetylacetone-derived Schiff bases towards rhenium(I) and (V) Polyhedron 28

(2009) 1174-1178

[26] T Jurca O Ramadan I Korobkov DS Richeson Employing sterically

encumbered bis(imino)pyridine ligands in support of fac-rhenium(I) carbonyls

J Organomet Chem 802 (2016) 27-31

[27] J Ho WY Lee KJT Koh PPF Lee YK Yan Rhenium(I) tricarbonyl

complexes of salicylaldehyde semicarbazones Synthesis crystal structures and

cytotoxicity J Inorg Biochem 119 (2013) 10-20

[28] B Machura A Świtlicka M Wolff J Kusz R Kruszynski Mono- and di-

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[29] B Machura M Jaworska P Lodowski Natural bond orbital analysis and

density functional study of linear and bent oxo-bridged dimers of rhenium(V)

J Mol Struc-Theochem 766 (2006) 1-8

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Highlights

bull Chromone rhenium(I) compounds

bull Simulated IR spectra

bull Low calculated RMSDs

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formulation of new rhenium radiopharmaceuticals This is illustrated by the facial

tricarbonylrhenium(I) complexes stability under physiological conditions where the

small size of the fac-[Re(CO)3]+ core allows binding to various biological entities [5-

6] However the next generation of potential rhenium radiopharmaceuticals requires

chelators which can stabilize the metal centre both in the low and high oxidation

states [7] Furthermore these multidentate chelators should also cater for the

inclusion of biologically active moieties which may aid in the target specific

biodistribution of the metallopharmaceuticals [8 9]

In our previous studies we have reported the isolation of oxorhenium(V) and

facial tricarbonylrhenium(I) complexes with Schiff bases encompassing uracil

chromone or benz(othiazoleimidazole) moieties [10-12] These multidentate Schiff

base chelators illustrated diverse coordination behaviours leading to mono- or

dinuclear rhenium compounds For example an unique dinuclear rhenium(I)

complex (micro-bzp)2[Re(CO)3]2 [Hbzp = N-(2-hydroxybenzylidene)-benzimidazole] has

a centralized 8-membered chelate ring formed by coordination of the benzimidazole

nitrogens to the individual rhenium atoms [11] Furthermore different

transformations of the chromone mono-imines 2-(2-thiolphenyliminomethyl)-4H-

chromen-4-one (Htch) and H3uch [5-((4-hydroxy-2-methoxy-2H-chromen-3-

yl)methyleneamino)-6-amino-13-dimethylpyrimidine-24(1H 3H)-dione] were

observed upon their coordination reactions with trans-[ReOBr3(PPh3)3] to afford

[ReO(Hns)] H2ns = bis-[(2-phenylthiolate)iminomethyl]-methyl-1-(2-

hydroxyphenyl)prop-2-en-1-one and [ReO(OCH3)(PPh3)(Huch)] [12]

As a continuation of our research studies on rhenium herein we consider the

coordination behaviours of multidentate diimines encompassing chromone moieties

This secondary metabolite chromone and its derivatives are known to induce

cytotoxic effects in breast cancer cell lines [13 14] Hence we report the coordination

reactions of [Re(CO)5Br] with the diimines N Nlsquo-bis(2-amino-3-

imino)methylenechromone-12-ethane (chret) and NNrsquo-bis((3-chromone)methylene)-

benzene-12-diamine (chb) to afford a novel dinuclear rhenium(I) compound fac-

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(Re(CO)3Br)2(micro-chret) (1) and a mononuclear compound fac-[Re(CO)3(bzch)Br] (2)

[bzch = 2-benzimidazole-4H-chromen-4-one]

N NO

O

O

Ochb

N NO

O

O

O

chret

NH2 H2N

N

HNO

O

bzch

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2 Experimental

21 Materials and methods

The reagents bromopentacarbonylrhenium(I) ethylenediamine

12-diaminobenzene 2-amino-3-formylchromone and 3-formylchromone were

obtained from Sigma Aldrich and used as received All solvents and common salts

were obtained from Merck SA Reagent grade toluene was dried over sodium wire

solvents were used without further purification The synthetic procedure and

characterization data for the free-ligand chret can be found in the online supporting

information document see Figs S1 S2 and S5 The diimine chb was obtained from

the condensation reaction of 12-diaminobenzene with a two-fold molar quantity of

3-formylchromone [15]

The infrared spectra were recorded on a Perkin-Elmer 100 spectrometer in the

4000 ndash 450 cm-1 range The 1H NMR spectra were obtained using a Bruker Avance

400 MHz spectrometer All NMR spectra were recorded in deuterated

dimethylsulphoxide UV-Vis spectra were recorded using a Perkin Elmer Lambda

25 The extinction coefficients (ε) are given in dm3mol-1cm-1 Melting points were

determined using a Stuart SMP3 melting point apparatus The conductivity

measurements were determined at 295K on a Radiometer R21M127CDM 230

conductivity and pH meter

22 fac-(Re(CO)3Br)2(micro-chret) (1)

A 11 molar reaction mixture of [Re(CO)5Br] (0050 g 0123 mmol) and chret (0049 g

0123 mmol) in 15 cm3 of anhydrous toluene was heated at reflux under nitrogen for

4 hrs The resultant reaction mixture was cooled to room temperature and filtered

An orange precipitate was dried under vacuum Pale orange X-ray quality

crystalline parallelograms were obtained from layering the precipitate with a 11

(vv) THFhexane over a period of five days MP = 215 - 220 ᴼC yield = 87

Conductivity (DMSO 10-3M) 1693 ohmcm2mol-1 IR (νmaxcm-1) ν(N-H) 2920 2850

(m) ν(CequivO) 2015 1871 (vs) ν(C=O) 1655 (s) ν(C=N) 1615 1613 (s) ν(O-C-O) 1464

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cm-1 (s) 1H NMR (295 K ppm) 1091 (br s 4H 2x NH2) 895 ndash 865 (m 6H H10

H12 H16 H19 H24 H26) 812 ndash 711 (m 4H H9 H11 H23 H25) 469 ndash 439 (m 4H

H17 H17rsquo H18 H18rsquo) UV-Vis (DMSO λmax(K M-1cm-1)) 269 nm (24159) 296 nm (sh

20140) 405 nm (sh 2464)

23 fac-[Re(CO)3(bzch)Br] (2)

The equimolar coordination reaction between [Re(CO)5Br] (0050 g 0123 mmol) and

chb (0052 g 0123 mmol) was conducted in 15 cm3 of anhydrous toluene heated at

reflux under nitrogen for 4 hrs The resultant reaction mixture was cooled to room

temperature and an orange precipitate was filtered and dried under vacuum Pale

orange cubic crystals suitable for X-ray analysis were obtained from dissolving the

precipitate in tetrahydrofuran and layering with hexane MP = 210 ndash 211 ᴼC yield =

93 Conductivity (DMSO 10-3M) 2372 ohmcm2mol-1 IR (νmaxcm-1) ν(N-H) 2915

(w) ν(CequivO) 2015 1871 (vs) ν(C=O) 1628 1607 (s) ν(C=N) 1567 (s) ν(O-C-O) 1461 (s) 1H NMR (295 K ppm) 969 (s 1H H1) 939 (s 1H NH) 827-722 (m 8H H3 H4

H5 H6 H12 H13 H14 H15) UV-Vis (DMSO λmax(K M-1cm-1)) 275 nm (sh 26107)

282 nm (27295) 309 nm (sh 22025) 394 nm (6614) 418 nm (sh 4394)

24 X-ray diffraction

The X-ray data for C28H18Br2N4O10Re23(C4H8O) and C19H10BrN2O5ReC7H8 were

recorded on a Bruker Apex Duo equipped with an Oxford Instruments Cryojet

operating at 100(2) K and an Incoatec microsource operating at 30W power Crystal

and structure refinement data are given in Table 1 Selected bond lengths and

angles are given in Tables 2 and 3 In both cases the data were collected with Mo Kα

(λ = 071073 Aring) radiation at a crystal-to-detector distance of 50 mm The following

conditions were used for data collection omega and phi scans with exposures taken

at 30 W X-ray power and 050ordm frame widths using APEX2 [16] The data were

reduced with the program SAINT [16] using outlier rejection scan speed scaling as

well as standard Lorentz and polarization correction factors A SADABS semi-

empirical multi-scan absorption correction [17] was applied to the data Direct

methods SHELX-2014 [18] and WinGX [19] were used to solve both structures All

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non-hydrogen atoms were located in the difference density map and refined

anisotropically with SHELX-2014 [20] All hydrogen atoms were included as

idealised contributors in the least squares process Their positions were calculated

using a standard riding model with C-Haromatic distances of 093 Aring and Uiso = 12 Ueq

C-Hmethylene distances of 099 Aring and Uiso = 12 Ueq and CndashHmethyl distances of 098 Aring and

Uiso = 15 Ueq The amine hydrogen atoms were located in the difference density

map and allowed to refine isotropically

25 Computational details

Molecular simulations were conducted with GAUSSIAN 09W [20] Geometry

optimizations of 1 and 2 were achieved through a DFT calculation using the B3LYP

functional with an accompanying hybrid basis set viz the 6-311G++ (d p) basis set

was applied to all the C H N O and Br and the LANL2DZ basis set which makes

use of effective core potentials applied to the metal centre [12] Prior to the

calculation the solvent molecules of recrystallization for the respective metal

complexes were omitted from their crystal structures and the resultant structures

were used as the starting conformers Good agreement was found between the

optimized and experimental geometrical parameters (refer to Tables 2 and 3) with

the minor deviations attributed to the fact that the gas phase optimized structures do

not account for intermolecular interactions or any short distance contacts The close

correlation between the optimized and geometrical parameters of the respective

complexes is further emphasized by the low calculated root-mean-square deviation

(RMSD) see Fig 1 The larger RMSD of 1 is mainly ascribed to the largely free

rotation of the C-C single bonds within the chret chelator Using the optimized

structure of the metal complex the lack of any negative Eigen values in the

frequency calculations confirmed that the structures are at global minima on their

individual potential energy surfaces [21]

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Fig 1 Overlay structures of the optimized and experimental crystal structures for the

respective complexes with their corresponding RMSD values The crystal structures are

shown in yellow while the optimized structures are given in blue

3 Results and Discussion

31 Synthesis spectral characterization and computational studies

The metallic compounds fac-(Re(CO)3Br)2(micro-chret) (1) and fac-

[Re(CO)3(bzch)Br] (2) [bzch = 2-benzimidazole-4H-chromen-4-one] were synthesized

under anaerobic conditions from the equimolar reaction of [Re(CO)5Br] with the

diimines chret and chb respectively In 1 the chret ligand bridges two fac-

[Re(CO)3Br] units while coordinating as a bidentate moiety to each metal centre via

its NiminoOketo donor sets Despite the use of anaerobic conditions X-ray studies of 2

revealed that the chb diimine underwent intraligand cyclization followed by the

hydrolysis of one of its imine bonds In fact the chloro rhenium(I) analogue fac-

[Re(CO)3(bzch)Cl] was similarly formed from the reaction of [Re(CO)5Cl] with the

Schiff base ligand 2-(2- aminophenyliminomethyl)-4H-chromen-4-one (H2pch) which

led to the transformation of the latter to a bzch moiety [11] However no

transformation of the diimine chb occured in the dinuclear ruthenium(III)

compound (micro-chb)[mer-RuCl3(PPh3)]2 where the neutral chb moiety bridges the two

cis-[RuIIICl3] cores via its ketonic oxygen and imino nitrogen atoms [15] In contrast

to 2rsquos centralized 1 2-((methylene)imino)-benzene moiety the flexible

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((imino)methylene)-12-ethane bridging moiety of 1 minimizes steric strain within its

chret chelator which effectively induces stability and prevents the transformation of

the chret ligand Furthermore compounds 1 and 2 exhibits good solubility in high

boiling point polar solvents including dimethylsulfoxide and dimethylformamide

while showing a relatively modest solubility in tetrahydrofuran and poor solubility

in chlorinated solvents such as chloroform The low molar conductivities [ΛM = 1693

and 2372 ohmcm2mol-1] of the metallic compounds indicates their neutrality in

DMSO

Broad vibrational bands are observed below 1700 cm-1 in the experimental IR

spectra of the metal complexes which could not be clearly assigned without the aid

of the simulated IR spectra of 1 and 2 see Figs S1 ndash S4 Both the experimental [2015

1871 cm-1 for 1 and 2] and simulated [2105 2018 2016 cm-1 for 1 and 2097 2017 1993

cm-1 for 2] IR spectra are dominated by the intense stretches of the carbonyl co-

ligands Similarly the ν(N-H) vibrations of 1 and 2 appear as weak intensity

vibrational bands in their respective simulated [3644 cm-1 for 1 and 3654 3289 cm-1

for 2] and experimental [2920 2850 cm-1 for 1 and 2915 cm-1 for 2] IR spectra The

simulated IR spectrum of 1 indicates distinctive vibrational bands associated with

the ketonic (at 1687 cm-1) imine (at 1567 cm-1) and ether (at 1469 cm-1) bonds

whereas the corresponding IR stretching frequencies can be found at 1655 cm-1 [for

ν(C=O)] 1464 cm-1 1615 [for ν(O-C-O)] and 1613 cm-1 [for ν(C=N)] in the

experimental IR spectrum of 1 Correlating the simulated IR spectrum of 2 with its

experimental IR spectrum revealed that the experimental vibrations for ν(C=O) are

found at 1628 and 1607 cm-1 while ν(C=N) and ν(O-C-O) appears at 1567 cm-1 and

1461 cm-1 respectively

In the proton NMR spectrum of 1 the aliphatic protons of the bridging ethane

moiety resonates as a multiplet between 469 and 439 ppm see Fig S6 A broad

singlet at 1091 ppm corresponds to the protons of the amino nitrogens of 1 but the

analogous protons were observed as two broad signals in the proton NMR spectrum

of the free-ligand chret see Fig S5 For 1 the aromatic protons of the chromone

moieties and the imino signal coalesce into two multiplets (viz 895 ndash 865 ppm and

812 ndash 711 ppm) in comparison to the corresponding well-resolved signals at 872

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ppm (for the imino protons) and 798 767 737 ppm (for the aromatic protons of the

chromone moieties) of the free-ligand chret The most intense signal in the 1H NMR

spectrum of 2 is due to the H1 proton positioned on the chromone moiety which

appears as a sharp singlet (at 969 ppm)

The benzimidazole proton in 2 resonates as an intense signal at 939 ppm

which integrates to one while the multiplet between 827 and 722 ppm are due to

the remaining aromatic peaks The presence of the pi-conjugated neutral chelators in

1 and 2 results in the occurrence of only intra-ligand - transitions in their UV-Vis

spectra see Figs S7 and S8 As expected no metal-based d-d transitions are

observed at more red-shifted regions due to the low-spin d6 electron configurations

of 1 and 2

32 Crystal structure of 1

Compound 1 co-crystallized with three tetrahydrofuran molecules of

recrystallization in its triclinic unit cell The crystal lattice of 1 is stabilized by a

network of classical intramolecular [Br1H4a-N4 = 273(4) Aring and Br2H2a-N2 =

260(4) Aring] and intermolecular hydrogen bonding [O11AH2b-N2 = 195(4) Aring and

O11BH4b-N4 = 191(5) Aring] see Fig S9 Collectively these hydrogen bonding

interactions allows molecules of 1 to pack in columns parallel to the [a]- and [b]-axes

The metal centres of 1 are positioned in the centre of the distorted

octahedrons which are largely imposed on by their constrained bite angles [O1-Re1-

N1 = 8452(7)ordm and N3-Re2-O6 = 8393(7)ordm] see Fig 2 Consequently the C2-Re1-Br1

[17685(8)ordm] O1-Re1-C3 [17741(9)ordm] C1-Re1-N1 [1762(1)ordm] Br2-Re2-C6 [17699(8)ordm]

C4-Re2-O6 [17641(9)ordm] and N3-Re2-C5 [1742(1)ordm] deviate all from linearity The

flexibility of the bridging ethane moiety affords narrower C=N-C [C18-N3-C19 =

1148(2)ordm and C16-N1-C17 = 1150(2)ordm] bond angles than the expected 120ordm for a bond

angle containing a central sp2 hybridized nitrogen Despite the influence of the

bridging ethane moiety the imino bonds [C16-N1 = 1286(4) Aring and C19-N3 =

1291(4) Aring] of 1 are in the range [1285(3) - 1312(6) Aring] observed for similar bonds

found in other Schiff bases [7 11 21 22 23] Across the respective octahedrons only

the Re1-C2 [1894(3) Aring] and Re2-C6 [1893(3) Aring] bonds are nearly equidistant which

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reflects similar trans-influence induced by the Br1 and Br2 atoms respectively

Hence the comparable cis-orientated organometallic bonds [Re1-C1 = 1942(3) Aring

Re1-C3 = 1897(3) Aring Re2-C4 = 1908(3) Aring and Re2-C5 = 1932(3) Aring] across the

octahedrons in 1 differs

The rhenium to ketonic [Re1-O1 = 2137(2) Aring and Re2-O6 = 2139(2) Aring] and

imino nitrogen [Re1-N1 = 2169(2) Aring and Re2-N3 = 2171(2) Aring] bonds are similar to

analogous bonds found within fac-[Re(CO)3(chrpychr)Br] (chrpychr = 2-(4-oxo-4H-

chromen-3-yl)-5H-chromeno[23-d]pyrimidin-5-one) and [(micro-O)ReOCl(amp)2]

(amp= 6-amino-3-methyl-1-phenyl-4-azahept-2-ene-1-one) [24 25] Bond orders with

the chret chelator is established based on the ketonic bonds [C14-O1 = 1259(4) Aring and

C28-O6 = 1261(3) Aring] being longer than the carbonyl bonds [eg C1-O3 = 1144(3) Aring]

but yet shorter than the ether bonds [eg C8-O2 = 1383(3) Aring and C21-O7 = 1347(4)

Aring] Also the localized C=C bonds in the chromone moeities remain intact after

coordination of the chret chelators as these C=C bonds [C7-C15 = 1414(4) Aring and

C20-C21 = 1411(4) Aring] are shorter than the C-C single bond [C17-C18 = 1537(3) Aring]

that constitutes the bridging ethane moeity

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Fig 2 An ORTEP view of compound 1 showing 50 probability displacement ellipsoids

and the atom labelling The tetrahydrofuran molecules of crystallization were omitted for

clarity

33 Crystal structure of 2

Four molecules of 2 occupies its monoclinic unit cell and each of these

molecules forms dimers with molecules of 2 in adjacent unit cells via classical

hydrogen-bonding interactions [Br1N2A-H2ABr1AN2-H = 257(3) Aring] see Fig

S10 Consequently molecules of 2 are self-assembled in columns aligned with the

[b]-axis Indicative to 1 the constrained bite angle [O1-Re-N1 = 8199(7)ordm] of 2 results

in the deviation of orthogonality in the opposing C17-Re-C19 [8690(1)ordm] bond angle

see Fig 3

The rhenium to halide bonds of 1 [Re1-Br1 = 26455(3) Aring and Re2-Br2 =

26377(3) Aring] and 2 [Re-Br = 26322(8) Aring] are comparable to those found in other facial

tricarbonyl rhenium complexes [26 27] All the remaining coordination bonds of 2

[Re-N1 = 2186(2) Aring Re-O1 = 2141(1) Aring Re-C17 = 1931(2) Aring Re-C18 = 1901(2) Aring

and Re-C19 = 1901(2) Aring] were similar to its chloro-analogue fac-[Re(CO)3(bzch)Cl]

viz Re-Oketone = 2137(2) Aring Re-Nbenzimidazole = 2179(2) Aring and Re-Ccarbonyl = 1929(2) Aring

1904(2) Aring 1898(2) Aring [11] Furthermore the double bond character of the C10-N1

bonds [1336(3) Aring] are clearly established when compared to the C-N bond lengths

[C10-N2 = 1358(3) Aring C16-N1 = 1401(3) Aring and C11-N2 = 1374(3) Aring] In addition the

bridging C9-C10 [1466(3) Aring] bond is single based on the more shorter localized C=C

[1365(3) Aring] chromone bond In turn the degrees of freedom around the C9-10 single

bond allows the chromone and benzimidazole plane to form a dihedral angle of

601ordm Also the benzimidazole and chromone moeities lies out of the plane of the

O1N1C19C17 mean basal plane by 1783ordm and 1837ordm respectively The toluene

molecule of recrystallization from an adjacent unit cell is nearly co-planar with the

bzch chelator of 1 indicating - interactions between this toluene molecule and the

bzch chelator (toluene Csp2 centroid to C9 = 3309 Aring and toluene Csp2 centroid to C10

= 3561 Aring)

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An evaluation of the experimental and optimized geometrical parameters for

the metal complexes reveals that the calculated intraligand bond distances [C17-C18

= 15374 Aring for 1 and C1-C9 = 13601 Aring for 2] and angles [O6-Re2-N3 = 83023ordm for 1

and O1-Re-N1 = 80800ordm for 2] compares well with their analogous experimental

geometrical parameters [C17-C18 = 1537(4) Aring for 1 C1-C9 = 1365(3) Aring for 2 O6-

Re2-N3 = 8393(7)ordm for 1 and O1-Re-N1 = 8199(7)ordm for 2] In addition the differences

in bond lengths found between comparable experimental [eg Re1-C1 = 1942(3) Aring

for 1 and Re-C19 = 1901(2) Aring] and optimized [eg Re1-C1 = 19344 Aring for 1 and Re-

C19 = 19034 Aring for 2] organometallic Re-CO bonds are not significant Discrepencies

found between the experimental [Re1-Br1 = 26455(3) Aring Re2-Br2 = 26377(3) Aring for 1

and Re-Br = 26322(8) Aring for 2] and calculated [Re1-Br1 = 272064 Aring Re2-Br2 = 272059

Aring for 1 and Re-Br = 266556 Aring for 2] rhenium to halide bonds are significant which

are ascribed to the rhenium atoms having lower calculated Natural Population

Analysis charges (0851 for Re12 in 1 and 0889 in 2) than the formal +I charge [28

29] The same trend is observed when examining the Re-Oketonic and Re-N

coordination bonds which were found to be longer in the computational models [eg

Re1-O1 = 21765 Aring Re1-N1 = 22224 Aring for 1 and Re-O1 = 22226 Aring Re-N1 = 23072 Aring

for 2] due to their lower Lewis acidic character of the metal centres than those in the

crystal structures [eg Re1-O1 = 2137(2) Aring Re1-N1 = 2169(2) Aring for 1 and Re-O1 =

2141(2) Aring Re-N1 = 2186(2) Aring for 2]

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Fig 3 An ORTEP view of complex 2 showing 50 probability displacement ellipsoids and

the atom labelling The toluene molecule of crystallization was omitted for clarity

Conclusion

Exploring the coordination behaviours of the diimine chret and chb afforded the di-

and mononuclear rhenium(I) compounds fac-(Re(CO)3Br)2(micro-chret) (1) and fac-

[Re(CO)3(bzch)Br] (2) The interpretation of the IR experimental spectra of the metal

compounds was supported by their simulated spectra calculated at the DFT level of

theory X-ray studies concured with the spectroscopic characterization revealing the

transformation of the chb diimine into the bzch chelator (in 2) and affirming the

coordination modes of the chb (in 1) and bzch (in 2) chelators In addition the 6-

membered chelate rings had a significant influence on the geometrical parameters of

the octahedral geometries of 1 and 2

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Supporting information

CCDC 1451521 and 1451522 contains crystallographic data for this article These data

can be obtained free of charge at wwwccdccamacukcontsretrievinghtml [or

from the Cambridge Crystallographic Data Centre (CCDC) 12 Union Road

Cambridge CB21EZ UK Fax +44(0)1223-336033 Email depositccdccamacuk]

Supplementary figures S1-S10 associated with this article can be found in the online

version

Acknowledgements

We are grateful to the University of KwaZulu-Natal and the National Research

Foundation of South Africa for financial support

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Table 1 Crystal data and structure refinement data

13(C4H8O) 2C7H8

Chemical formula C28H18Br2N4O10Re23(C4H8O) C19H10BrN2O5ReC7H8

Formula weight 131899 70453

TemperatureK 100(2) 100(2)

Crystal system Triclinic Monoclinic

Space group P-1 P21n

Unit cell dimensions (Ǻ deg) a = 128859(6) a = 12400(5)

b = 131199(6) b = 11778(5)

c = 149558(7) c = 16316(5)

α= 114601(2) α = 90000(5)

β = 98138(2) β = 92469(5)

γ = 102350(2) γ = 90000(5)

Crystal size (mm) 013 x 006 x 005 009 x 006 x 005

V(Aring3) 216873 (18) 238007(16)

Z 2 4

Density (calc) (mgm3) 2020 1966

Absorption coefficient (mm-1) 749 682

F(000) 1268 1352

θ range for data collection

(deg)

16 291 20 290

Reflections measured 41497 23824

Observed reflections [Igt2σ(I)] 10414 5621

Independent reflections 11421 6310

DataRestraintsparameters 114210566 56210321

Goodness of fit on F2 103 103

Observed R wR2 0018 0043 0020 0042

Rint 0018 0027

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Table 2 Selected bond lengths [Aring] and bond angles [deg] for 1 The RMSD of 1 is 0720 Aring

Experimental Optimized

Re1-Br1 26455(3) 272064 Re2-Br2 26377(3) 272059 Re1-O1 2137(2) 21765 Re2-O6 2139(2) 21764 Re1-N1 2169(2) 22224 Re2-N3 2171(2) 22224 Re1-C1 1942(3) 19344 Re1-C2 1894(3) 19091 Re1-C3 1897(3) 19071 Re2-C4 1908(3) 19071 Re2-C5 1932(3) 19091 Re2-C6 1893(2) 19343 C16-N1 1286(4) 12919 C19-N3 1291(4) 12919 C14-O1 1259(4) 12502 C28-O6 1261(3) 12503 C1-O3 1144(3) 11492 C8-O2 1383(3) 13796 C21-O7 1347(4) 13440 C7-C15 1414(4) 14102 C20-C21 1411(4) 14103 C17-C18 1537(3) 15374 O1-Re1-N1 8452(7) 83027 O6-Re2-N3 8393(7) 83023 C2-Re1-Br1 17685(8) 177228 O1-Re1-C3 17741(9) 176550 C1-Re1-N1 1762(1) 174310 Br2-Re2-C6 17699(8) 177236 C4-Re2-O6 17641(9) 176545 N3-Re2-C5 1742(1) 174309 C16-N1-C17 1150(2) 114920 C18-N3-C19 1148(2) 114920

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Table 3 Selected bond lengths [Aring] and bond angles [deg] for 2 The RMSD of 2 is 0267 Aring

Experimental Optimized

Re-Br 26322(8) 266556 Re-N1 2186(2) 23072 Re-O1 2141(2) 22226 Re-C17 1931(2) 19263 Re-C18 1901(2) 19150 Re-C19 1901(2) 19034 C9-C10 1466(3) 14608 C1-C9 1365(3) 13601 O1-Re-N1 8199(7) 80800 C17-Re-C19 8690(1) 88380 Br-Re-C18 17582(7) 176266

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[7] K Potgieter P Mayer TIA Gerber IN Booysen Coordination behaviour of

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[11] IN Booysen MB Ismail OQ Munro Mono- and dinuclear rhenium(I)

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[12] IN Booysen MB Ismail MP Akerman Coordination behaviour of chromone

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[13] S Bhatnagar S Sahir P Kackar S Kaushik MK Dave A Shukla A Goel

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[14] M Recanatini A Bisi A Cavalli F Belluti S Gobbi A Rampa P Valenti M

Palzer A Palusczak RW Hartmann A New Class of Nonsteroidal Aromatase

Inhibitorsthinsp Design and Synthesis of Chromone and Xanthone Derivatives and

Inhibition of the P450 Enzymes Aromatase and 17α-HydroxylaseC1720-

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[15] IN Booysen A Adebisi MP Akerman OQ Munro B Xulu Coordination of

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[16] Bruker APEX2 SAINT and SADABS Bruker AXS Inc (2010) Madison

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[18] GM Sheldrick A short history of SHELX Acta Cryst A64 (2008) 112-122

[19] LJ Farrugia WinGX and ORTEP for Windows an update J Appl Cryst 45

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[20] MJ Frisch GW Trucks HB Schlegel GE Scuseria MA Robb JR

Cheeseman G Scalmani V Barone B Mennucci GA Petersson H Nakatsuji

M Caricato X Li HP Hratchian AF Izmaylov J Bloino G Zheng JL

Sonnenberg M Hada M Ehara K Toyota R Fukuda J Hasegawa M Ishida

T Nakajima Y Honda O Kitao H Nakai T Vreven JA Montgomery Jr JE

Peralta F Ogliaro M Bearpark JJ Heyd E Brothers KN Kudin VN

Staroverov R Kobayashi J Normand K Raghavachari A Rendell JC

Burant SS Iyengar J Tomasi M Cossi N Rega JM Millam M Klene JE

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Knox JB Cross V Bakken C Adamo J Jaramillo R Gomperts RE

Stratmann O Yazyev AJ Austin R Cammi C Pomelli JW Ochterski RL

Martin K Morokuma VG Zakrzewski GA Voth P Salvador JJ

Dannenberg S Dapprich AD Daniels O Farkas JB Foresman JV Ortiz J

Cioslowski DJ Fox GAUSSIAN 09 (Revision A01) Gaussian

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[21] A Brink HG Visser A Roodt Novel imino rhenium(I) tricarbonyl complexes

of salicylidene-derived ligands Synthesis X-ray crystallographic studies

spectroscopic characterization and DFT calculations Polyhedron 52 (2013) 416-

423

[22] J Mukiza TIA Gerber EC Hosten Decarboxylation of 5-amino-orotic acid

and a Schiff base derivative by rhenium(V) Inorg Chem Comm 57 (2015) 54-

57

[23] K Potgieter P Mayer T Gerber N Yumata E Hosten I Booysen R Betz M

Ismail B van Brecht Rhenium(I) tricarbonyl complexes with multidentate

nitrogen-donor derivatives Polyhedron 49 (2013) 67-73

[24] IN Booysen I Ebinumoliseh MP Akerman B Xulu A rhenium(I) compound

bearing a dimerized chromone NO bidentate chelator Inorg Chem Comm 62

(2015) 8-10

[25] P Mayer TIA Gerber B Buyambo A Abrahams Coordination behaviour of

acetylacetone-derived Schiff bases towards rhenium(I) and (V) Polyhedron 28

(2009) 1174-1178

[26] T Jurca O Ramadan I Korobkov DS Richeson Employing sterically

encumbered bis(imino)pyridine ligands in support of fac-rhenium(I) carbonyls

J Organomet Chem 802 (2016) 27-31

[27] J Ho WY Lee KJT Koh PPF Lee YK Yan Rhenium(I) tricarbonyl

complexes of salicylaldehyde semicarbazones Synthesis crystal structures and

cytotoxicity J Inorg Biochem 119 (2013) 10-20

[28] B Machura A Świtlicka M Wolff J Kusz R Kruszynski Mono- and di-

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[29] B Machura M Jaworska P Lodowski Natural bond orbital analysis and

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J Mol Struc-Theochem 766 (2006) 1-8

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Highlights

bull Chromone rhenium(I) compounds

bull Simulated IR spectra

bull Low calculated RMSDs

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(Re(CO)3Br)2(micro-chret) (1) and a mononuclear compound fac-[Re(CO)3(bzch)Br] (2)

[bzch = 2-benzimidazole-4H-chromen-4-one]

N NO

O

O

Ochb

N NO

O

O

O

chret

NH2 H2N

N

HNO

O

bzch

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2 Experimental

21 Materials and methods

The reagents bromopentacarbonylrhenium(I) ethylenediamine

12-diaminobenzene 2-amino-3-formylchromone and 3-formylchromone were

obtained from Sigma Aldrich and used as received All solvents and common salts

were obtained from Merck SA Reagent grade toluene was dried over sodium wire

solvents were used without further purification The synthetic procedure and

characterization data for the free-ligand chret can be found in the online supporting

information document see Figs S1 S2 and S5 The diimine chb was obtained from

the condensation reaction of 12-diaminobenzene with a two-fold molar quantity of

3-formylchromone [15]

The infrared spectra were recorded on a Perkin-Elmer 100 spectrometer in the

4000 ndash 450 cm-1 range The 1H NMR spectra were obtained using a Bruker Avance

400 MHz spectrometer All NMR spectra were recorded in deuterated

dimethylsulphoxide UV-Vis spectra were recorded using a Perkin Elmer Lambda

25 The extinction coefficients (ε) are given in dm3mol-1cm-1 Melting points were

determined using a Stuart SMP3 melting point apparatus The conductivity

measurements were determined at 295K on a Radiometer R21M127CDM 230

conductivity and pH meter

22 fac-(Re(CO)3Br)2(micro-chret) (1)

A 11 molar reaction mixture of [Re(CO)5Br] (0050 g 0123 mmol) and chret (0049 g

0123 mmol) in 15 cm3 of anhydrous toluene was heated at reflux under nitrogen for

4 hrs The resultant reaction mixture was cooled to room temperature and filtered

An orange precipitate was dried under vacuum Pale orange X-ray quality

crystalline parallelograms were obtained from layering the precipitate with a 11

(vv) THFhexane over a period of five days MP = 215 - 220 ᴼC yield = 87

Conductivity (DMSO 10-3M) 1693 ohmcm2mol-1 IR (νmaxcm-1) ν(N-H) 2920 2850

(m) ν(CequivO) 2015 1871 (vs) ν(C=O) 1655 (s) ν(C=N) 1615 1613 (s) ν(O-C-O) 1464

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cm-1 (s) 1H NMR (295 K ppm) 1091 (br s 4H 2x NH2) 895 ndash 865 (m 6H H10

H12 H16 H19 H24 H26) 812 ndash 711 (m 4H H9 H11 H23 H25) 469 ndash 439 (m 4H

H17 H17rsquo H18 H18rsquo) UV-Vis (DMSO λmax(K M-1cm-1)) 269 nm (24159) 296 nm (sh

20140) 405 nm (sh 2464)

23 fac-[Re(CO)3(bzch)Br] (2)

The equimolar coordination reaction between [Re(CO)5Br] (0050 g 0123 mmol) and

chb (0052 g 0123 mmol) was conducted in 15 cm3 of anhydrous toluene heated at

reflux under nitrogen for 4 hrs The resultant reaction mixture was cooled to room

temperature and an orange precipitate was filtered and dried under vacuum Pale

orange cubic crystals suitable for X-ray analysis were obtained from dissolving the

precipitate in tetrahydrofuran and layering with hexane MP = 210 ndash 211 ᴼC yield =

93 Conductivity (DMSO 10-3M) 2372 ohmcm2mol-1 IR (νmaxcm-1) ν(N-H) 2915

(w) ν(CequivO) 2015 1871 (vs) ν(C=O) 1628 1607 (s) ν(C=N) 1567 (s) ν(O-C-O) 1461 (s) 1H NMR (295 K ppm) 969 (s 1H H1) 939 (s 1H NH) 827-722 (m 8H H3 H4

H5 H6 H12 H13 H14 H15) UV-Vis (DMSO λmax(K M-1cm-1)) 275 nm (sh 26107)

282 nm (27295) 309 nm (sh 22025) 394 nm (6614) 418 nm (sh 4394)

24 X-ray diffraction

The X-ray data for C28H18Br2N4O10Re23(C4H8O) and C19H10BrN2O5ReC7H8 were

recorded on a Bruker Apex Duo equipped with an Oxford Instruments Cryojet

operating at 100(2) K and an Incoatec microsource operating at 30W power Crystal

and structure refinement data are given in Table 1 Selected bond lengths and

angles are given in Tables 2 and 3 In both cases the data were collected with Mo Kα

(λ = 071073 Aring) radiation at a crystal-to-detector distance of 50 mm The following

conditions were used for data collection omega and phi scans with exposures taken

at 30 W X-ray power and 050ordm frame widths using APEX2 [16] The data were

reduced with the program SAINT [16] using outlier rejection scan speed scaling as

well as standard Lorentz and polarization correction factors A SADABS semi-

empirical multi-scan absorption correction [17] was applied to the data Direct

methods SHELX-2014 [18] and WinGX [19] were used to solve both structures All

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non-hydrogen atoms were located in the difference density map and refined

anisotropically with SHELX-2014 [20] All hydrogen atoms were included as

idealised contributors in the least squares process Their positions were calculated

using a standard riding model with C-Haromatic distances of 093 Aring and Uiso = 12 Ueq

C-Hmethylene distances of 099 Aring and Uiso = 12 Ueq and CndashHmethyl distances of 098 Aring and

Uiso = 15 Ueq The amine hydrogen atoms were located in the difference density

map and allowed to refine isotropically

25 Computational details

Molecular simulations were conducted with GAUSSIAN 09W [20] Geometry

optimizations of 1 and 2 were achieved through a DFT calculation using the B3LYP

functional with an accompanying hybrid basis set viz the 6-311G++ (d p) basis set

was applied to all the C H N O and Br and the LANL2DZ basis set which makes

use of effective core potentials applied to the metal centre [12] Prior to the

calculation the solvent molecules of recrystallization for the respective metal

complexes were omitted from their crystal structures and the resultant structures

were used as the starting conformers Good agreement was found between the

optimized and experimental geometrical parameters (refer to Tables 2 and 3) with

the minor deviations attributed to the fact that the gas phase optimized structures do

not account for intermolecular interactions or any short distance contacts The close

correlation between the optimized and geometrical parameters of the respective

complexes is further emphasized by the low calculated root-mean-square deviation

(RMSD) see Fig 1 The larger RMSD of 1 is mainly ascribed to the largely free

rotation of the C-C single bonds within the chret chelator Using the optimized

structure of the metal complex the lack of any negative Eigen values in the

frequency calculations confirmed that the structures are at global minima on their

individual potential energy surfaces [21]

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Fig 1 Overlay structures of the optimized and experimental crystal structures for the

respective complexes with their corresponding RMSD values The crystal structures are

shown in yellow while the optimized structures are given in blue

3 Results and Discussion

31 Synthesis spectral characterization and computational studies

The metallic compounds fac-(Re(CO)3Br)2(micro-chret) (1) and fac-

[Re(CO)3(bzch)Br] (2) [bzch = 2-benzimidazole-4H-chromen-4-one] were synthesized

under anaerobic conditions from the equimolar reaction of [Re(CO)5Br] with the

diimines chret and chb respectively In 1 the chret ligand bridges two fac-

[Re(CO)3Br] units while coordinating as a bidentate moiety to each metal centre via

its NiminoOketo donor sets Despite the use of anaerobic conditions X-ray studies of 2

revealed that the chb diimine underwent intraligand cyclization followed by the

hydrolysis of one of its imine bonds In fact the chloro rhenium(I) analogue fac-

[Re(CO)3(bzch)Cl] was similarly formed from the reaction of [Re(CO)5Cl] with the

Schiff base ligand 2-(2- aminophenyliminomethyl)-4H-chromen-4-one (H2pch) which

led to the transformation of the latter to a bzch moiety [11] However no

transformation of the diimine chb occured in the dinuclear ruthenium(III)

compound (micro-chb)[mer-RuCl3(PPh3)]2 where the neutral chb moiety bridges the two

cis-[RuIIICl3] cores via its ketonic oxygen and imino nitrogen atoms [15] In contrast

to 2rsquos centralized 1 2-((methylene)imino)-benzene moiety the flexible

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((imino)methylene)-12-ethane bridging moiety of 1 minimizes steric strain within its

chret chelator which effectively induces stability and prevents the transformation of

the chret ligand Furthermore compounds 1 and 2 exhibits good solubility in high

boiling point polar solvents including dimethylsulfoxide and dimethylformamide

while showing a relatively modest solubility in tetrahydrofuran and poor solubility

in chlorinated solvents such as chloroform The low molar conductivities [ΛM = 1693

and 2372 ohmcm2mol-1] of the metallic compounds indicates their neutrality in

DMSO

Broad vibrational bands are observed below 1700 cm-1 in the experimental IR

spectra of the metal complexes which could not be clearly assigned without the aid

of the simulated IR spectra of 1 and 2 see Figs S1 ndash S4 Both the experimental [2015

1871 cm-1 for 1 and 2] and simulated [2105 2018 2016 cm-1 for 1 and 2097 2017 1993

cm-1 for 2] IR spectra are dominated by the intense stretches of the carbonyl co-

ligands Similarly the ν(N-H) vibrations of 1 and 2 appear as weak intensity

vibrational bands in their respective simulated [3644 cm-1 for 1 and 3654 3289 cm-1

for 2] and experimental [2920 2850 cm-1 for 1 and 2915 cm-1 for 2] IR spectra The

simulated IR spectrum of 1 indicates distinctive vibrational bands associated with

the ketonic (at 1687 cm-1) imine (at 1567 cm-1) and ether (at 1469 cm-1) bonds

whereas the corresponding IR stretching frequencies can be found at 1655 cm-1 [for

ν(C=O)] 1464 cm-1 1615 [for ν(O-C-O)] and 1613 cm-1 [for ν(C=N)] in the

experimental IR spectrum of 1 Correlating the simulated IR spectrum of 2 with its

experimental IR spectrum revealed that the experimental vibrations for ν(C=O) are

found at 1628 and 1607 cm-1 while ν(C=N) and ν(O-C-O) appears at 1567 cm-1 and

1461 cm-1 respectively

In the proton NMR spectrum of 1 the aliphatic protons of the bridging ethane

moiety resonates as a multiplet between 469 and 439 ppm see Fig S6 A broad

singlet at 1091 ppm corresponds to the protons of the amino nitrogens of 1 but the

analogous protons were observed as two broad signals in the proton NMR spectrum

of the free-ligand chret see Fig S5 For 1 the aromatic protons of the chromone

moieties and the imino signal coalesce into two multiplets (viz 895 ndash 865 ppm and

812 ndash 711 ppm) in comparison to the corresponding well-resolved signals at 872

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ppm (for the imino protons) and 798 767 737 ppm (for the aromatic protons of the

chromone moieties) of the free-ligand chret The most intense signal in the 1H NMR

spectrum of 2 is due to the H1 proton positioned on the chromone moiety which

appears as a sharp singlet (at 969 ppm)

The benzimidazole proton in 2 resonates as an intense signal at 939 ppm

which integrates to one while the multiplet between 827 and 722 ppm are due to

the remaining aromatic peaks The presence of the pi-conjugated neutral chelators in

1 and 2 results in the occurrence of only intra-ligand - transitions in their UV-Vis

spectra see Figs S7 and S8 As expected no metal-based d-d transitions are

observed at more red-shifted regions due to the low-spin d6 electron configurations

of 1 and 2

32 Crystal structure of 1

Compound 1 co-crystallized with three tetrahydrofuran molecules of

recrystallization in its triclinic unit cell The crystal lattice of 1 is stabilized by a

network of classical intramolecular [Br1H4a-N4 = 273(4) Aring and Br2H2a-N2 =

260(4) Aring] and intermolecular hydrogen bonding [O11AH2b-N2 = 195(4) Aring and

O11BH4b-N4 = 191(5) Aring] see Fig S9 Collectively these hydrogen bonding

interactions allows molecules of 1 to pack in columns parallel to the [a]- and [b]-axes

The metal centres of 1 are positioned in the centre of the distorted

octahedrons which are largely imposed on by their constrained bite angles [O1-Re1-

N1 = 8452(7)ordm and N3-Re2-O6 = 8393(7)ordm] see Fig 2 Consequently the C2-Re1-Br1

[17685(8)ordm] O1-Re1-C3 [17741(9)ordm] C1-Re1-N1 [1762(1)ordm] Br2-Re2-C6 [17699(8)ordm]

C4-Re2-O6 [17641(9)ordm] and N3-Re2-C5 [1742(1)ordm] deviate all from linearity The

flexibility of the bridging ethane moiety affords narrower C=N-C [C18-N3-C19 =

1148(2)ordm and C16-N1-C17 = 1150(2)ordm] bond angles than the expected 120ordm for a bond

angle containing a central sp2 hybridized nitrogen Despite the influence of the

bridging ethane moiety the imino bonds [C16-N1 = 1286(4) Aring and C19-N3 =

1291(4) Aring] of 1 are in the range [1285(3) - 1312(6) Aring] observed for similar bonds

found in other Schiff bases [7 11 21 22 23] Across the respective octahedrons only

the Re1-C2 [1894(3) Aring] and Re2-C6 [1893(3) Aring] bonds are nearly equidistant which

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reflects similar trans-influence induced by the Br1 and Br2 atoms respectively

Hence the comparable cis-orientated organometallic bonds [Re1-C1 = 1942(3) Aring

Re1-C3 = 1897(3) Aring Re2-C4 = 1908(3) Aring and Re2-C5 = 1932(3) Aring] across the

octahedrons in 1 differs

The rhenium to ketonic [Re1-O1 = 2137(2) Aring and Re2-O6 = 2139(2) Aring] and

imino nitrogen [Re1-N1 = 2169(2) Aring and Re2-N3 = 2171(2) Aring] bonds are similar to

analogous bonds found within fac-[Re(CO)3(chrpychr)Br] (chrpychr = 2-(4-oxo-4H-

chromen-3-yl)-5H-chromeno[23-d]pyrimidin-5-one) and [(micro-O)ReOCl(amp)2]

(amp= 6-amino-3-methyl-1-phenyl-4-azahept-2-ene-1-one) [24 25] Bond orders with

the chret chelator is established based on the ketonic bonds [C14-O1 = 1259(4) Aring and

C28-O6 = 1261(3) Aring] being longer than the carbonyl bonds [eg C1-O3 = 1144(3) Aring]

but yet shorter than the ether bonds [eg C8-O2 = 1383(3) Aring and C21-O7 = 1347(4)

Aring] Also the localized C=C bonds in the chromone moeities remain intact after

coordination of the chret chelators as these C=C bonds [C7-C15 = 1414(4) Aring and

C20-C21 = 1411(4) Aring] are shorter than the C-C single bond [C17-C18 = 1537(3) Aring]

that constitutes the bridging ethane moeity

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Fig 2 An ORTEP view of compound 1 showing 50 probability displacement ellipsoids

and the atom labelling The tetrahydrofuran molecules of crystallization were omitted for

clarity

33 Crystal structure of 2

Four molecules of 2 occupies its monoclinic unit cell and each of these

molecules forms dimers with molecules of 2 in adjacent unit cells via classical

hydrogen-bonding interactions [Br1N2A-H2ABr1AN2-H = 257(3) Aring] see Fig

S10 Consequently molecules of 2 are self-assembled in columns aligned with the

[b]-axis Indicative to 1 the constrained bite angle [O1-Re-N1 = 8199(7)ordm] of 2 results

in the deviation of orthogonality in the opposing C17-Re-C19 [8690(1)ordm] bond angle

see Fig 3

The rhenium to halide bonds of 1 [Re1-Br1 = 26455(3) Aring and Re2-Br2 =

26377(3) Aring] and 2 [Re-Br = 26322(8) Aring] are comparable to those found in other facial

tricarbonyl rhenium complexes [26 27] All the remaining coordination bonds of 2

[Re-N1 = 2186(2) Aring Re-O1 = 2141(1) Aring Re-C17 = 1931(2) Aring Re-C18 = 1901(2) Aring

and Re-C19 = 1901(2) Aring] were similar to its chloro-analogue fac-[Re(CO)3(bzch)Cl]

viz Re-Oketone = 2137(2) Aring Re-Nbenzimidazole = 2179(2) Aring and Re-Ccarbonyl = 1929(2) Aring

1904(2) Aring 1898(2) Aring [11] Furthermore the double bond character of the C10-N1

bonds [1336(3) Aring] are clearly established when compared to the C-N bond lengths

[C10-N2 = 1358(3) Aring C16-N1 = 1401(3) Aring and C11-N2 = 1374(3) Aring] In addition the

bridging C9-C10 [1466(3) Aring] bond is single based on the more shorter localized C=C

[1365(3) Aring] chromone bond In turn the degrees of freedom around the C9-10 single

bond allows the chromone and benzimidazole plane to form a dihedral angle of

601ordm Also the benzimidazole and chromone moeities lies out of the plane of the

O1N1C19C17 mean basal plane by 1783ordm and 1837ordm respectively The toluene

molecule of recrystallization from an adjacent unit cell is nearly co-planar with the

bzch chelator of 1 indicating - interactions between this toluene molecule and the

bzch chelator (toluene Csp2 centroid to C9 = 3309 Aring and toluene Csp2 centroid to C10

= 3561 Aring)

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An evaluation of the experimental and optimized geometrical parameters for

the metal complexes reveals that the calculated intraligand bond distances [C17-C18

= 15374 Aring for 1 and C1-C9 = 13601 Aring for 2] and angles [O6-Re2-N3 = 83023ordm for 1

and O1-Re-N1 = 80800ordm for 2] compares well with their analogous experimental

geometrical parameters [C17-C18 = 1537(4) Aring for 1 C1-C9 = 1365(3) Aring for 2 O6-

Re2-N3 = 8393(7)ordm for 1 and O1-Re-N1 = 8199(7)ordm for 2] In addition the differences

in bond lengths found between comparable experimental [eg Re1-C1 = 1942(3) Aring

for 1 and Re-C19 = 1901(2) Aring] and optimized [eg Re1-C1 = 19344 Aring for 1 and Re-

C19 = 19034 Aring for 2] organometallic Re-CO bonds are not significant Discrepencies

found between the experimental [Re1-Br1 = 26455(3) Aring Re2-Br2 = 26377(3) Aring for 1

and Re-Br = 26322(8) Aring for 2] and calculated [Re1-Br1 = 272064 Aring Re2-Br2 = 272059

Aring for 1 and Re-Br = 266556 Aring for 2] rhenium to halide bonds are significant which

are ascribed to the rhenium atoms having lower calculated Natural Population

Analysis charges (0851 for Re12 in 1 and 0889 in 2) than the formal +I charge [28

29] The same trend is observed when examining the Re-Oketonic and Re-N

coordination bonds which were found to be longer in the computational models [eg

Re1-O1 = 21765 Aring Re1-N1 = 22224 Aring for 1 and Re-O1 = 22226 Aring Re-N1 = 23072 Aring

for 2] due to their lower Lewis acidic character of the metal centres than those in the

crystal structures [eg Re1-O1 = 2137(2) Aring Re1-N1 = 2169(2) Aring for 1 and Re-O1 =

2141(2) Aring Re-N1 = 2186(2) Aring for 2]

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Fig 3 An ORTEP view of complex 2 showing 50 probability displacement ellipsoids and

the atom labelling The toluene molecule of crystallization was omitted for clarity

Conclusion

Exploring the coordination behaviours of the diimine chret and chb afforded the di-

and mononuclear rhenium(I) compounds fac-(Re(CO)3Br)2(micro-chret) (1) and fac-

[Re(CO)3(bzch)Br] (2) The interpretation of the IR experimental spectra of the metal

compounds was supported by their simulated spectra calculated at the DFT level of

theory X-ray studies concured with the spectroscopic characterization revealing the

transformation of the chb diimine into the bzch chelator (in 2) and affirming the

coordination modes of the chb (in 1) and bzch (in 2) chelators In addition the 6-

membered chelate rings had a significant influence on the geometrical parameters of

the octahedral geometries of 1 and 2

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Supporting information

CCDC 1451521 and 1451522 contains crystallographic data for this article These data

can be obtained free of charge at wwwccdccamacukcontsretrievinghtml [or

from the Cambridge Crystallographic Data Centre (CCDC) 12 Union Road

Cambridge CB21EZ UK Fax +44(0)1223-336033 Email depositccdccamacuk]

Supplementary figures S1-S10 associated with this article can be found in the online

version

Acknowledgements

We are grateful to the University of KwaZulu-Natal and the National Research

Foundation of South Africa for financial support

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Table 1 Crystal data and structure refinement data

13(C4H8O) 2C7H8

Chemical formula C28H18Br2N4O10Re23(C4H8O) C19H10BrN2O5ReC7H8

Formula weight 131899 70453

TemperatureK 100(2) 100(2)

Crystal system Triclinic Monoclinic

Space group P-1 P21n

Unit cell dimensions (Ǻ deg) a = 128859(6) a = 12400(5)

b = 131199(6) b = 11778(5)

c = 149558(7) c = 16316(5)

α= 114601(2) α = 90000(5)

β = 98138(2) β = 92469(5)

γ = 102350(2) γ = 90000(5)

Crystal size (mm) 013 x 006 x 005 009 x 006 x 005

V(Aring3) 216873 (18) 238007(16)

Z 2 4

Density (calc) (mgm3) 2020 1966

Absorption coefficient (mm-1) 749 682

F(000) 1268 1352

θ range for data collection

(deg)

16 291 20 290

Reflections measured 41497 23824

Observed reflections [Igt2σ(I)] 10414 5621

Independent reflections 11421 6310

DataRestraintsparameters 114210566 56210321

Goodness of fit on F2 103 103

Observed R wR2 0018 0043 0020 0042

Rint 0018 0027

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Table 2 Selected bond lengths [Aring] and bond angles [deg] for 1 The RMSD of 1 is 0720 Aring

Experimental Optimized

Re1-Br1 26455(3) 272064 Re2-Br2 26377(3) 272059 Re1-O1 2137(2) 21765 Re2-O6 2139(2) 21764 Re1-N1 2169(2) 22224 Re2-N3 2171(2) 22224 Re1-C1 1942(3) 19344 Re1-C2 1894(3) 19091 Re1-C3 1897(3) 19071 Re2-C4 1908(3) 19071 Re2-C5 1932(3) 19091 Re2-C6 1893(2) 19343 C16-N1 1286(4) 12919 C19-N3 1291(4) 12919 C14-O1 1259(4) 12502 C28-O6 1261(3) 12503 C1-O3 1144(3) 11492 C8-O2 1383(3) 13796 C21-O7 1347(4) 13440 C7-C15 1414(4) 14102 C20-C21 1411(4) 14103 C17-C18 1537(3) 15374 O1-Re1-N1 8452(7) 83027 O6-Re2-N3 8393(7) 83023 C2-Re1-Br1 17685(8) 177228 O1-Re1-C3 17741(9) 176550 C1-Re1-N1 1762(1) 174310 Br2-Re2-C6 17699(8) 177236 C4-Re2-O6 17641(9) 176545 N3-Re2-C5 1742(1) 174309 C16-N1-C17 1150(2) 114920 C18-N3-C19 1148(2) 114920

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Table 3 Selected bond lengths [Aring] and bond angles [deg] for 2 The RMSD of 2 is 0267 Aring

Experimental Optimized

Re-Br 26322(8) 266556 Re-N1 2186(2) 23072 Re-O1 2141(2) 22226 Re-C17 1931(2) 19263 Re-C18 1901(2) 19150 Re-C19 1901(2) 19034 C9-C10 1466(3) 14608 C1-C9 1365(3) 13601 O1-Re-N1 8199(7) 80800 C17-Re-C19 8690(1) 88380 Br-Re-C18 17582(7) 176266

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complexes of salicylaldehyde semicarbazones Synthesis crystal structures and

cytotoxicity J Inorg Biochem 119 (2013) 10-20

[28] B Machura A Świtlicka M Wolff J Kusz R Kruszynski Mono- and di-

nuclear oxorhenium(V) complexes of 47-diphenyl-110-phenanthroline

Polyhedron 28 (2009) 3999-4009

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[29] B Machura M Jaworska P Lodowski Natural bond orbital analysis and

density functional study of linear and bent oxo-bridged dimers of rhenium(V)

J Mol Struc-Theochem 766 (2006) 1-8

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Highlights

bull Chromone rhenium(I) compounds

bull Simulated IR spectra

bull Low calculated RMSDs

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2 Experimental

21 Materials and methods

The reagents bromopentacarbonylrhenium(I) ethylenediamine

12-diaminobenzene 2-amino-3-formylchromone and 3-formylchromone were

obtained from Sigma Aldrich and used as received All solvents and common salts

were obtained from Merck SA Reagent grade toluene was dried over sodium wire

solvents were used without further purification The synthetic procedure and

characterization data for the free-ligand chret can be found in the online supporting

information document see Figs S1 S2 and S5 The diimine chb was obtained from

the condensation reaction of 12-diaminobenzene with a two-fold molar quantity of

3-formylchromone [15]

The infrared spectra were recorded on a Perkin-Elmer 100 spectrometer in the

4000 ndash 450 cm-1 range The 1H NMR spectra were obtained using a Bruker Avance

400 MHz spectrometer All NMR spectra were recorded in deuterated

dimethylsulphoxide UV-Vis spectra were recorded using a Perkin Elmer Lambda

25 The extinction coefficients (ε) are given in dm3mol-1cm-1 Melting points were

determined using a Stuart SMP3 melting point apparatus The conductivity

measurements were determined at 295K on a Radiometer R21M127CDM 230

conductivity and pH meter

22 fac-(Re(CO)3Br)2(micro-chret) (1)

A 11 molar reaction mixture of [Re(CO)5Br] (0050 g 0123 mmol) and chret (0049 g

0123 mmol) in 15 cm3 of anhydrous toluene was heated at reflux under nitrogen for

4 hrs The resultant reaction mixture was cooled to room temperature and filtered

An orange precipitate was dried under vacuum Pale orange X-ray quality

crystalline parallelograms were obtained from layering the precipitate with a 11

(vv) THFhexane over a period of five days MP = 215 - 220 ᴼC yield = 87

Conductivity (DMSO 10-3M) 1693 ohmcm2mol-1 IR (νmaxcm-1) ν(N-H) 2920 2850

(m) ν(CequivO) 2015 1871 (vs) ν(C=O) 1655 (s) ν(C=N) 1615 1613 (s) ν(O-C-O) 1464

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cm-1 (s) 1H NMR (295 K ppm) 1091 (br s 4H 2x NH2) 895 ndash 865 (m 6H H10

H12 H16 H19 H24 H26) 812 ndash 711 (m 4H H9 H11 H23 H25) 469 ndash 439 (m 4H

H17 H17rsquo H18 H18rsquo) UV-Vis (DMSO λmax(K M-1cm-1)) 269 nm (24159) 296 nm (sh

20140) 405 nm (sh 2464)

23 fac-[Re(CO)3(bzch)Br] (2)

The equimolar coordination reaction between [Re(CO)5Br] (0050 g 0123 mmol) and

chb (0052 g 0123 mmol) was conducted in 15 cm3 of anhydrous toluene heated at

reflux under nitrogen for 4 hrs The resultant reaction mixture was cooled to room

temperature and an orange precipitate was filtered and dried under vacuum Pale

orange cubic crystals suitable for X-ray analysis were obtained from dissolving the

precipitate in tetrahydrofuran and layering with hexane MP = 210 ndash 211 ᴼC yield =

93 Conductivity (DMSO 10-3M) 2372 ohmcm2mol-1 IR (νmaxcm-1) ν(N-H) 2915

(w) ν(CequivO) 2015 1871 (vs) ν(C=O) 1628 1607 (s) ν(C=N) 1567 (s) ν(O-C-O) 1461 (s) 1H NMR (295 K ppm) 969 (s 1H H1) 939 (s 1H NH) 827-722 (m 8H H3 H4

H5 H6 H12 H13 H14 H15) UV-Vis (DMSO λmax(K M-1cm-1)) 275 nm (sh 26107)

282 nm (27295) 309 nm (sh 22025) 394 nm (6614) 418 nm (sh 4394)

24 X-ray diffraction

The X-ray data for C28H18Br2N4O10Re23(C4H8O) and C19H10BrN2O5ReC7H8 were

recorded on a Bruker Apex Duo equipped with an Oxford Instruments Cryojet

operating at 100(2) K and an Incoatec microsource operating at 30W power Crystal

and structure refinement data are given in Table 1 Selected bond lengths and

angles are given in Tables 2 and 3 In both cases the data were collected with Mo Kα

(λ = 071073 Aring) radiation at a crystal-to-detector distance of 50 mm The following

conditions were used for data collection omega and phi scans with exposures taken

at 30 W X-ray power and 050ordm frame widths using APEX2 [16] The data were

reduced with the program SAINT [16] using outlier rejection scan speed scaling as

well as standard Lorentz and polarization correction factors A SADABS semi-

empirical multi-scan absorption correction [17] was applied to the data Direct

methods SHELX-2014 [18] and WinGX [19] were used to solve both structures All

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non-hydrogen atoms were located in the difference density map and refined

anisotropically with SHELX-2014 [20] All hydrogen atoms were included as

idealised contributors in the least squares process Their positions were calculated

using a standard riding model with C-Haromatic distances of 093 Aring and Uiso = 12 Ueq

C-Hmethylene distances of 099 Aring and Uiso = 12 Ueq and CndashHmethyl distances of 098 Aring and

Uiso = 15 Ueq The amine hydrogen atoms were located in the difference density

map and allowed to refine isotropically

25 Computational details

Molecular simulations were conducted with GAUSSIAN 09W [20] Geometry

optimizations of 1 and 2 were achieved through a DFT calculation using the B3LYP

functional with an accompanying hybrid basis set viz the 6-311G++ (d p) basis set

was applied to all the C H N O and Br and the LANL2DZ basis set which makes

use of effective core potentials applied to the metal centre [12] Prior to the

calculation the solvent molecules of recrystallization for the respective metal

complexes were omitted from their crystal structures and the resultant structures

were used as the starting conformers Good agreement was found between the

optimized and experimental geometrical parameters (refer to Tables 2 and 3) with

the minor deviations attributed to the fact that the gas phase optimized structures do

not account for intermolecular interactions or any short distance contacts The close

correlation between the optimized and geometrical parameters of the respective

complexes is further emphasized by the low calculated root-mean-square deviation

(RMSD) see Fig 1 The larger RMSD of 1 is mainly ascribed to the largely free

rotation of the C-C single bonds within the chret chelator Using the optimized

structure of the metal complex the lack of any negative Eigen values in the

frequency calculations confirmed that the structures are at global minima on their

individual potential energy surfaces [21]

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Fig 1 Overlay structures of the optimized and experimental crystal structures for the

respective complexes with their corresponding RMSD values The crystal structures are

shown in yellow while the optimized structures are given in blue

3 Results and Discussion

31 Synthesis spectral characterization and computational studies

The metallic compounds fac-(Re(CO)3Br)2(micro-chret) (1) and fac-

[Re(CO)3(bzch)Br] (2) [bzch = 2-benzimidazole-4H-chromen-4-one] were synthesized

under anaerobic conditions from the equimolar reaction of [Re(CO)5Br] with the

diimines chret and chb respectively In 1 the chret ligand bridges two fac-

[Re(CO)3Br] units while coordinating as a bidentate moiety to each metal centre via

its NiminoOketo donor sets Despite the use of anaerobic conditions X-ray studies of 2

revealed that the chb diimine underwent intraligand cyclization followed by the

hydrolysis of one of its imine bonds In fact the chloro rhenium(I) analogue fac-

[Re(CO)3(bzch)Cl] was similarly formed from the reaction of [Re(CO)5Cl] with the

Schiff base ligand 2-(2- aminophenyliminomethyl)-4H-chromen-4-one (H2pch) which

led to the transformation of the latter to a bzch moiety [11] However no

transformation of the diimine chb occured in the dinuclear ruthenium(III)

compound (micro-chb)[mer-RuCl3(PPh3)]2 where the neutral chb moiety bridges the two

cis-[RuIIICl3] cores via its ketonic oxygen and imino nitrogen atoms [15] In contrast

to 2rsquos centralized 1 2-((methylene)imino)-benzene moiety the flexible

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((imino)methylene)-12-ethane bridging moiety of 1 minimizes steric strain within its

chret chelator which effectively induces stability and prevents the transformation of

the chret ligand Furthermore compounds 1 and 2 exhibits good solubility in high

boiling point polar solvents including dimethylsulfoxide and dimethylformamide

while showing a relatively modest solubility in tetrahydrofuran and poor solubility

in chlorinated solvents such as chloroform The low molar conductivities [ΛM = 1693

and 2372 ohmcm2mol-1] of the metallic compounds indicates their neutrality in

DMSO

Broad vibrational bands are observed below 1700 cm-1 in the experimental IR

spectra of the metal complexes which could not be clearly assigned without the aid

of the simulated IR spectra of 1 and 2 see Figs S1 ndash S4 Both the experimental [2015

1871 cm-1 for 1 and 2] and simulated [2105 2018 2016 cm-1 for 1 and 2097 2017 1993

cm-1 for 2] IR spectra are dominated by the intense stretches of the carbonyl co-

ligands Similarly the ν(N-H) vibrations of 1 and 2 appear as weak intensity

vibrational bands in their respective simulated [3644 cm-1 for 1 and 3654 3289 cm-1

for 2] and experimental [2920 2850 cm-1 for 1 and 2915 cm-1 for 2] IR spectra The

simulated IR spectrum of 1 indicates distinctive vibrational bands associated with

the ketonic (at 1687 cm-1) imine (at 1567 cm-1) and ether (at 1469 cm-1) bonds

whereas the corresponding IR stretching frequencies can be found at 1655 cm-1 [for

ν(C=O)] 1464 cm-1 1615 [for ν(O-C-O)] and 1613 cm-1 [for ν(C=N)] in the

experimental IR spectrum of 1 Correlating the simulated IR spectrum of 2 with its

experimental IR spectrum revealed that the experimental vibrations for ν(C=O) are

found at 1628 and 1607 cm-1 while ν(C=N) and ν(O-C-O) appears at 1567 cm-1 and

1461 cm-1 respectively

In the proton NMR spectrum of 1 the aliphatic protons of the bridging ethane

moiety resonates as a multiplet between 469 and 439 ppm see Fig S6 A broad

singlet at 1091 ppm corresponds to the protons of the amino nitrogens of 1 but the

analogous protons were observed as two broad signals in the proton NMR spectrum

of the free-ligand chret see Fig S5 For 1 the aromatic protons of the chromone

moieties and the imino signal coalesce into two multiplets (viz 895 ndash 865 ppm and

812 ndash 711 ppm) in comparison to the corresponding well-resolved signals at 872

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ppm (for the imino protons) and 798 767 737 ppm (for the aromatic protons of the

chromone moieties) of the free-ligand chret The most intense signal in the 1H NMR

spectrum of 2 is due to the H1 proton positioned on the chromone moiety which

appears as a sharp singlet (at 969 ppm)

The benzimidazole proton in 2 resonates as an intense signal at 939 ppm

which integrates to one while the multiplet between 827 and 722 ppm are due to

the remaining aromatic peaks The presence of the pi-conjugated neutral chelators in

1 and 2 results in the occurrence of only intra-ligand - transitions in their UV-Vis

spectra see Figs S7 and S8 As expected no metal-based d-d transitions are

observed at more red-shifted regions due to the low-spin d6 electron configurations

of 1 and 2

32 Crystal structure of 1

Compound 1 co-crystallized with three tetrahydrofuran molecules of

recrystallization in its triclinic unit cell The crystal lattice of 1 is stabilized by a

network of classical intramolecular [Br1H4a-N4 = 273(4) Aring and Br2H2a-N2 =

260(4) Aring] and intermolecular hydrogen bonding [O11AH2b-N2 = 195(4) Aring and

O11BH4b-N4 = 191(5) Aring] see Fig S9 Collectively these hydrogen bonding

interactions allows molecules of 1 to pack in columns parallel to the [a]- and [b]-axes

The metal centres of 1 are positioned in the centre of the distorted

octahedrons which are largely imposed on by their constrained bite angles [O1-Re1-

N1 = 8452(7)ordm and N3-Re2-O6 = 8393(7)ordm] see Fig 2 Consequently the C2-Re1-Br1

[17685(8)ordm] O1-Re1-C3 [17741(9)ordm] C1-Re1-N1 [1762(1)ordm] Br2-Re2-C6 [17699(8)ordm]

C4-Re2-O6 [17641(9)ordm] and N3-Re2-C5 [1742(1)ordm] deviate all from linearity The

flexibility of the bridging ethane moiety affords narrower C=N-C [C18-N3-C19 =

1148(2)ordm and C16-N1-C17 = 1150(2)ordm] bond angles than the expected 120ordm for a bond

angle containing a central sp2 hybridized nitrogen Despite the influence of the

bridging ethane moiety the imino bonds [C16-N1 = 1286(4) Aring and C19-N3 =

1291(4) Aring] of 1 are in the range [1285(3) - 1312(6) Aring] observed for similar bonds

found in other Schiff bases [7 11 21 22 23] Across the respective octahedrons only

the Re1-C2 [1894(3) Aring] and Re2-C6 [1893(3) Aring] bonds are nearly equidistant which

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reflects similar trans-influence induced by the Br1 and Br2 atoms respectively

Hence the comparable cis-orientated organometallic bonds [Re1-C1 = 1942(3) Aring

Re1-C3 = 1897(3) Aring Re2-C4 = 1908(3) Aring and Re2-C5 = 1932(3) Aring] across the

octahedrons in 1 differs

The rhenium to ketonic [Re1-O1 = 2137(2) Aring and Re2-O6 = 2139(2) Aring] and

imino nitrogen [Re1-N1 = 2169(2) Aring and Re2-N3 = 2171(2) Aring] bonds are similar to

analogous bonds found within fac-[Re(CO)3(chrpychr)Br] (chrpychr = 2-(4-oxo-4H-

chromen-3-yl)-5H-chromeno[23-d]pyrimidin-5-one) and [(micro-O)ReOCl(amp)2]

(amp= 6-amino-3-methyl-1-phenyl-4-azahept-2-ene-1-one) [24 25] Bond orders with

the chret chelator is established based on the ketonic bonds [C14-O1 = 1259(4) Aring and

C28-O6 = 1261(3) Aring] being longer than the carbonyl bonds [eg C1-O3 = 1144(3) Aring]

but yet shorter than the ether bonds [eg C8-O2 = 1383(3) Aring and C21-O7 = 1347(4)

Aring] Also the localized C=C bonds in the chromone moeities remain intact after

coordination of the chret chelators as these C=C bonds [C7-C15 = 1414(4) Aring and

C20-C21 = 1411(4) Aring] are shorter than the C-C single bond [C17-C18 = 1537(3) Aring]

that constitutes the bridging ethane moeity

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Fig 2 An ORTEP view of compound 1 showing 50 probability displacement ellipsoids

and the atom labelling The tetrahydrofuran molecules of crystallization were omitted for

clarity

33 Crystal structure of 2

Four molecules of 2 occupies its monoclinic unit cell and each of these

molecules forms dimers with molecules of 2 in adjacent unit cells via classical

hydrogen-bonding interactions [Br1N2A-H2ABr1AN2-H = 257(3) Aring] see Fig

S10 Consequently molecules of 2 are self-assembled in columns aligned with the

[b]-axis Indicative to 1 the constrained bite angle [O1-Re-N1 = 8199(7)ordm] of 2 results

in the deviation of orthogonality in the opposing C17-Re-C19 [8690(1)ordm] bond angle

see Fig 3

The rhenium to halide bonds of 1 [Re1-Br1 = 26455(3) Aring and Re2-Br2 =

26377(3) Aring] and 2 [Re-Br = 26322(8) Aring] are comparable to those found in other facial

tricarbonyl rhenium complexes [26 27] All the remaining coordination bonds of 2

[Re-N1 = 2186(2) Aring Re-O1 = 2141(1) Aring Re-C17 = 1931(2) Aring Re-C18 = 1901(2) Aring

and Re-C19 = 1901(2) Aring] were similar to its chloro-analogue fac-[Re(CO)3(bzch)Cl]

viz Re-Oketone = 2137(2) Aring Re-Nbenzimidazole = 2179(2) Aring and Re-Ccarbonyl = 1929(2) Aring

1904(2) Aring 1898(2) Aring [11] Furthermore the double bond character of the C10-N1

bonds [1336(3) Aring] are clearly established when compared to the C-N bond lengths

[C10-N2 = 1358(3) Aring C16-N1 = 1401(3) Aring and C11-N2 = 1374(3) Aring] In addition the

bridging C9-C10 [1466(3) Aring] bond is single based on the more shorter localized C=C

[1365(3) Aring] chromone bond In turn the degrees of freedom around the C9-10 single

bond allows the chromone and benzimidazole plane to form a dihedral angle of

601ordm Also the benzimidazole and chromone moeities lies out of the plane of the

O1N1C19C17 mean basal plane by 1783ordm and 1837ordm respectively The toluene

molecule of recrystallization from an adjacent unit cell is nearly co-planar with the

bzch chelator of 1 indicating - interactions between this toluene molecule and the

bzch chelator (toluene Csp2 centroid to C9 = 3309 Aring and toluene Csp2 centroid to C10

= 3561 Aring)

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An evaluation of the experimental and optimized geometrical parameters for

the metal complexes reveals that the calculated intraligand bond distances [C17-C18

= 15374 Aring for 1 and C1-C9 = 13601 Aring for 2] and angles [O6-Re2-N3 = 83023ordm for 1

and O1-Re-N1 = 80800ordm for 2] compares well with their analogous experimental

geometrical parameters [C17-C18 = 1537(4) Aring for 1 C1-C9 = 1365(3) Aring for 2 O6-

Re2-N3 = 8393(7)ordm for 1 and O1-Re-N1 = 8199(7)ordm for 2] In addition the differences

in bond lengths found between comparable experimental [eg Re1-C1 = 1942(3) Aring

for 1 and Re-C19 = 1901(2) Aring] and optimized [eg Re1-C1 = 19344 Aring for 1 and Re-

C19 = 19034 Aring for 2] organometallic Re-CO bonds are not significant Discrepencies

found between the experimental [Re1-Br1 = 26455(3) Aring Re2-Br2 = 26377(3) Aring for 1

and Re-Br = 26322(8) Aring for 2] and calculated [Re1-Br1 = 272064 Aring Re2-Br2 = 272059

Aring for 1 and Re-Br = 266556 Aring for 2] rhenium to halide bonds are significant which

are ascribed to the rhenium atoms having lower calculated Natural Population

Analysis charges (0851 for Re12 in 1 and 0889 in 2) than the formal +I charge [28

29] The same trend is observed when examining the Re-Oketonic and Re-N

coordination bonds which were found to be longer in the computational models [eg

Re1-O1 = 21765 Aring Re1-N1 = 22224 Aring for 1 and Re-O1 = 22226 Aring Re-N1 = 23072 Aring

for 2] due to their lower Lewis acidic character of the metal centres than those in the

crystal structures [eg Re1-O1 = 2137(2) Aring Re1-N1 = 2169(2) Aring for 1 and Re-O1 =

2141(2) Aring Re-N1 = 2186(2) Aring for 2]

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Fig 3 An ORTEP view of complex 2 showing 50 probability displacement ellipsoids and

the atom labelling The toluene molecule of crystallization was omitted for clarity

Conclusion

Exploring the coordination behaviours of the diimine chret and chb afforded the di-

and mononuclear rhenium(I) compounds fac-(Re(CO)3Br)2(micro-chret) (1) and fac-

[Re(CO)3(bzch)Br] (2) The interpretation of the IR experimental spectra of the metal

compounds was supported by their simulated spectra calculated at the DFT level of

theory X-ray studies concured with the spectroscopic characterization revealing the

transformation of the chb diimine into the bzch chelator (in 2) and affirming the

coordination modes of the chb (in 1) and bzch (in 2) chelators In addition the 6-

membered chelate rings had a significant influence on the geometrical parameters of

the octahedral geometries of 1 and 2

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Supporting information

CCDC 1451521 and 1451522 contains crystallographic data for this article These data

can be obtained free of charge at wwwccdccamacukcontsretrievinghtml [or

from the Cambridge Crystallographic Data Centre (CCDC) 12 Union Road

Cambridge CB21EZ UK Fax +44(0)1223-336033 Email depositccdccamacuk]

Supplementary figures S1-S10 associated with this article can be found in the online

version

Acknowledgements

We are grateful to the University of KwaZulu-Natal and the National Research

Foundation of South Africa for financial support

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Table 1 Crystal data and structure refinement data

13(C4H8O) 2C7H8

Chemical formula C28H18Br2N4O10Re23(C4H8O) C19H10BrN2O5ReC7H8

Formula weight 131899 70453

TemperatureK 100(2) 100(2)

Crystal system Triclinic Monoclinic

Space group P-1 P21n

Unit cell dimensions (Ǻ deg) a = 128859(6) a = 12400(5)

b = 131199(6) b = 11778(5)

c = 149558(7) c = 16316(5)

α= 114601(2) α = 90000(5)

β = 98138(2) β = 92469(5)

γ = 102350(2) γ = 90000(5)

Crystal size (mm) 013 x 006 x 005 009 x 006 x 005

V(Aring3) 216873 (18) 238007(16)

Z 2 4

Density (calc) (mgm3) 2020 1966

Absorption coefficient (mm-1) 749 682

F(000) 1268 1352

θ range for data collection

(deg)

16 291 20 290

Reflections measured 41497 23824

Observed reflections [Igt2σ(I)] 10414 5621

Independent reflections 11421 6310

DataRestraintsparameters 114210566 56210321

Goodness of fit on F2 103 103

Observed R wR2 0018 0043 0020 0042

Rint 0018 0027

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Table 2 Selected bond lengths [Aring] and bond angles [deg] for 1 The RMSD of 1 is 0720 Aring

Experimental Optimized

Re1-Br1 26455(3) 272064 Re2-Br2 26377(3) 272059 Re1-O1 2137(2) 21765 Re2-O6 2139(2) 21764 Re1-N1 2169(2) 22224 Re2-N3 2171(2) 22224 Re1-C1 1942(3) 19344 Re1-C2 1894(3) 19091 Re1-C3 1897(3) 19071 Re2-C4 1908(3) 19071 Re2-C5 1932(3) 19091 Re2-C6 1893(2) 19343 C16-N1 1286(4) 12919 C19-N3 1291(4) 12919 C14-O1 1259(4) 12502 C28-O6 1261(3) 12503 C1-O3 1144(3) 11492 C8-O2 1383(3) 13796 C21-O7 1347(4) 13440 C7-C15 1414(4) 14102 C20-C21 1411(4) 14103 C17-C18 1537(3) 15374 O1-Re1-N1 8452(7) 83027 O6-Re2-N3 8393(7) 83023 C2-Re1-Br1 17685(8) 177228 O1-Re1-C3 17741(9) 176550 C1-Re1-N1 1762(1) 174310 Br2-Re2-C6 17699(8) 177236 C4-Re2-O6 17641(9) 176545 N3-Re2-C5 1742(1) 174309 C16-N1-C17 1150(2) 114920 C18-N3-C19 1148(2) 114920

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Table 3 Selected bond lengths [Aring] and bond angles [deg] for 2 The RMSD of 2 is 0267 Aring

Experimental Optimized

Re-Br 26322(8) 266556 Re-N1 2186(2) 23072 Re-O1 2141(2) 22226 Re-C17 1931(2) 19263 Re-C18 1901(2) 19150 Re-C19 1901(2) 19034 C9-C10 1466(3) 14608 C1-C9 1365(3) 13601 O1-Re-N1 8199(7) 80800 C17-Re-C19 8690(1) 88380 Br-Re-C18 17582(7) 176266

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[14] M Recanatini A Bisi A Cavalli F Belluti S Gobbi A Rampa P Valenti M

Palzer A Palusczak RW Hartmann A New Class of Nonsteroidal Aromatase

Inhibitorsthinsp Design and Synthesis of Chromone and Xanthone Derivatives and

Inhibition of the P450 Enzymes Aromatase and 17α-HydroxylaseC1720-

Lyase J Med Chem 44 (2001) 672-680

[15] IN Booysen A Adebisi MP Akerman OQ Munro B Xulu Coordination of

di- and triimine ligands at ruthenium(II) and ruthenium(III) centers structural

electrochemical and radical scavenging studies J Coord Chem (2016) doi

1010800095897220161177177

[16] Bruker APEX2 SAINT and SADABS Bruker AXS Inc (2010) Madison

Wisconsin USA

[17] RH Blessing An empirical correction for absorption anisotropy Acta Cryst

A51 (1995) 33-38

[18] GM Sheldrick A short history of SHELX Acta Cryst A64 (2008) 112-122

[19] LJ Farrugia WinGX and ORTEP for Windows an update J Appl Cryst 45

(2012) 849-854

[20] MJ Frisch GW Trucks HB Schlegel GE Scuseria MA Robb JR

Cheeseman G Scalmani V Barone B Mennucci GA Petersson H Nakatsuji

M Caricato X Li HP Hratchian AF Izmaylov J Bloino G Zheng JL

Sonnenberg M Hada M Ehara K Toyota R Fukuda J Hasegawa M Ishida

T Nakajima Y Honda O Kitao H Nakai T Vreven JA Montgomery Jr JE

Peralta F Ogliaro M Bearpark JJ Heyd E Brothers KN Kudin VN

Staroverov R Kobayashi J Normand K Raghavachari A Rendell JC

Burant SS Iyengar J Tomasi M Cossi N Rega JM Millam M Klene JE

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Knox JB Cross V Bakken C Adamo J Jaramillo R Gomperts RE

Stratmann O Yazyev AJ Austin R Cammi C Pomelli JW Ochterski RL

Martin K Morokuma VG Zakrzewski GA Voth P Salvador JJ

Dannenberg S Dapprich AD Daniels O Farkas JB Foresman JV Ortiz J

Cioslowski DJ Fox GAUSSIAN 09 (Revision A01) Gaussian

IncWallingford CT (2009)

[21] A Brink HG Visser A Roodt Novel imino rhenium(I) tricarbonyl complexes

of salicylidene-derived ligands Synthesis X-ray crystallographic studies

spectroscopic characterization and DFT calculations Polyhedron 52 (2013) 416-

423

[22] J Mukiza TIA Gerber EC Hosten Decarboxylation of 5-amino-orotic acid

and a Schiff base derivative by rhenium(V) Inorg Chem Comm 57 (2015) 54-

57

[23] K Potgieter P Mayer T Gerber N Yumata E Hosten I Booysen R Betz M

Ismail B van Brecht Rhenium(I) tricarbonyl complexes with multidentate

nitrogen-donor derivatives Polyhedron 49 (2013) 67-73

[24] IN Booysen I Ebinumoliseh MP Akerman B Xulu A rhenium(I) compound

bearing a dimerized chromone NO bidentate chelator Inorg Chem Comm 62

(2015) 8-10

[25] P Mayer TIA Gerber B Buyambo A Abrahams Coordination behaviour of

acetylacetone-derived Schiff bases towards rhenium(I) and (V) Polyhedron 28

(2009) 1174-1178

[26] T Jurca O Ramadan I Korobkov DS Richeson Employing sterically

encumbered bis(imino)pyridine ligands in support of fac-rhenium(I) carbonyls

J Organomet Chem 802 (2016) 27-31

[27] J Ho WY Lee KJT Koh PPF Lee YK Yan Rhenium(I) tricarbonyl

complexes of salicylaldehyde semicarbazones Synthesis crystal structures and

cytotoxicity J Inorg Biochem 119 (2013) 10-20

[28] B Machura A Świtlicka M Wolff J Kusz R Kruszynski Mono- and di-

nuclear oxorhenium(V) complexes of 47-diphenyl-110-phenanthroline

Polyhedron 28 (2009) 3999-4009

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[29] B Machura M Jaworska P Lodowski Natural bond orbital analysis and

density functional study of linear and bent oxo-bridged dimers of rhenium(V)

J Mol Struc-Theochem 766 (2006) 1-8

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Highlights

bull Chromone rhenium(I) compounds

bull Simulated IR spectra

bull Low calculated RMSDs

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cm-1 (s) 1H NMR (295 K ppm) 1091 (br s 4H 2x NH2) 895 ndash 865 (m 6H H10

H12 H16 H19 H24 H26) 812 ndash 711 (m 4H H9 H11 H23 H25) 469 ndash 439 (m 4H

H17 H17rsquo H18 H18rsquo) UV-Vis (DMSO λmax(K M-1cm-1)) 269 nm (24159) 296 nm (sh

20140) 405 nm (sh 2464)

23 fac-[Re(CO)3(bzch)Br] (2)

The equimolar coordination reaction between [Re(CO)5Br] (0050 g 0123 mmol) and

chb (0052 g 0123 mmol) was conducted in 15 cm3 of anhydrous toluene heated at

reflux under nitrogen for 4 hrs The resultant reaction mixture was cooled to room

temperature and an orange precipitate was filtered and dried under vacuum Pale

orange cubic crystals suitable for X-ray analysis were obtained from dissolving the

precipitate in tetrahydrofuran and layering with hexane MP = 210 ndash 211 ᴼC yield =

93 Conductivity (DMSO 10-3M) 2372 ohmcm2mol-1 IR (νmaxcm-1) ν(N-H) 2915

(w) ν(CequivO) 2015 1871 (vs) ν(C=O) 1628 1607 (s) ν(C=N) 1567 (s) ν(O-C-O) 1461 (s) 1H NMR (295 K ppm) 969 (s 1H H1) 939 (s 1H NH) 827-722 (m 8H H3 H4

H5 H6 H12 H13 H14 H15) UV-Vis (DMSO λmax(K M-1cm-1)) 275 nm (sh 26107)

282 nm (27295) 309 nm (sh 22025) 394 nm (6614) 418 nm (sh 4394)

24 X-ray diffraction

The X-ray data for C28H18Br2N4O10Re23(C4H8O) and C19H10BrN2O5ReC7H8 were

recorded on a Bruker Apex Duo equipped with an Oxford Instruments Cryojet

operating at 100(2) K and an Incoatec microsource operating at 30W power Crystal

and structure refinement data are given in Table 1 Selected bond lengths and

angles are given in Tables 2 and 3 In both cases the data were collected with Mo Kα

(λ = 071073 Aring) radiation at a crystal-to-detector distance of 50 mm The following

conditions were used for data collection omega and phi scans with exposures taken

at 30 W X-ray power and 050ordm frame widths using APEX2 [16] The data were

reduced with the program SAINT [16] using outlier rejection scan speed scaling as

well as standard Lorentz and polarization correction factors A SADABS semi-

empirical multi-scan absorption correction [17] was applied to the data Direct

methods SHELX-2014 [18] and WinGX [19] were used to solve both structures All

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non-hydrogen atoms were located in the difference density map and refined

anisotropically with SHELX-2014 [20] All hydrogen atoms were included as

idealised contributors in the least squares process Their positions were calculated

using a standard riding model with C-Haromatic distances of 093 Aring and Uiso = 12 Ueq

C-Hmethylene distances of 099 Aring and Uiso = 12 Ueq and CndashHmethyl distances of 098 Aring and

Uiso = 15 Ueq The amine hydrogen atoms were located in the difference density

map and allowed to refine isotropically

25 Computational details

Molecular simulations were conducted with GAUSSIAN 09W [20] Geometry

optimizations of 1 and 2 were achieved through a DFT calculation using the B3LYP

functional with an accompanying hybrid basis set viz the 6-311G++ (d p) basis set

was applied to all the C H N O and Br and the LANL2DZ basis set which makes

use of effective core potentials applied to the metal centre [12] Prior to the

calculation the solvent molecules of recrystallization for the respective metal

complexes were omitted from their crystal structures and the resultant structures

were used as the starting conformers Good agreement was found between the

optimized and experimental geometrical parameters (refer to Tables 2 and 3) with

the minor deviations attributed to the fact that the gas phase optimized structures do

not account for intermolecular interactions or any short distance contacts The close

correlation between the optimized and geometrical parameters of the respective

complexes is further emphasized by the low calculated root-mean-square deviation

(RMSD) see Fig 1 The larger RMSD of 1 is mainly ascribed to the largely free

rotation of the C-C single bonds within the chret chelator Using the optimized

structure of the metal complex the lack of any negative Eigen values in the

frequency calculations confirmed that the structures are at global minima on their

individual potential energy surfaces [21]

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Fig 1 Overlay structures of the optimized and experimental crystal structures for the

respective complexes with their corresponding RMSD values The crystal structures are

shown in yellow while the optimized structures are given in blue

3 Results and Discussion

31 Synthesis spectral characterization and computational studies

The metallic compounds fac-(Re(CO)3Br)2(micro-chret) (1) and fac-

[Re(CO)3(bzch)Br] (2) [bzch = 2-benzimidazole-4H-chromen-4-one] were synthesized

under anaerobic conditions from the equimolar reaction of [Re(CO)5Br] with the

diimines chret and chb respectively In 1 the chret ligand bridges two fac-

[Re(CO)3Br] units while coordinating as a bidentate moiety to each metal centre via

its NiminoOketo donor sets Despite the use of anaerobic conditions X-ray studies of 2

revealed that the chb diimine underwent intraligand cyclization followed by the

hydrolysis of one of its imine bonds In fact the chloro rhenium(I) analogue fac-

[Re(CO)3(bzch)Cl] was similarly formed from the reaction of [Re(CO)5Cl] with the

Schiff base ligand 2-(2- aminophenyliminomethyl)-4H-chromen-4-one (H2pch) which

led to the transformation of the latter to a bzch moiety [11] However no

transformation of the diimine chb occured in the dinuclear ruthenium(III)

compound (micro-chb)[mer-RuCl3(PPh3)]2 where the neutral chb moiety bridges the two

cis-[RuIIICl3] cores via its ketonic oxygen and imino nitrogen atoms [15] In contrast

to 2rsquos centralized 1 2-((methylene)imino)-benzene moiety the flexible

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((imino)methylene)-12-ethane bridging moiety of 1 minimizes steric strain within its

chret chelator which effectively induces stability and prevents the transformation of

the chret ligand Furthermore compounds 1 and 2 exhibits good solubility in high

boiling point polar solvents including dimethylsulfoxide and dimethylformamide

while showing a relatively modest solubility in tetrahydrofuran and poor solubility

in chlorinated solvents such as chloroform The low molar conductivities [ΛM = 1693

and 2372 ohmcm2mol-1] of the metallic compounds indicates their neutrality in

DMSO

Broad vibrational bands are observed below 1700 cm-1 in the experimental IR

spectra of the metal complexes which could not be clearly assigned without the aid

of the simulated IR spectra of 1 and 2 see Figs S1 ndash S4 Both the experimental [2015

1871 cm-1 for 1 and 2] and simulated [2105 2018 2016 cm-1 for 1 and 2097 2017 1993

cm-1 for 2] IR spectra are dominated by the intense stretches of the carbonyl co-

ligands Similarly the ν(N-H) vibrations of 1 and 2 appear as weak intensity

vibrational bands in their respective simulated [3644 cm-1 for 1 and 3654 3289 cm-1

for 2] and experimental [2920 2850 cm-1 for 1 and 2915 cm-1 for 2] IR spectra The

simulated IR spectrum of 1 indicates distinctive vibrational bands associated with

the ketonic (at 1687 cm-1) imine (at 1567 cm-1) and ether (at 1469 cm-1) bonds

whereas the corresponding IR stretching frequencies can be found at 1655 cm-1 [for

ν(C=O)] 1464 cm-1 1615 [for ν(O-C-O)] and 1613 cm-1 [for ν(C=N)] in the

experimental IR spectrum of 1 Correlating the simulated IR spectrum of 2 with its

experimental IR spectrum revealed that the experimental vibrations for ν(C=O) are

found at 1628 and 1607 cm-1 while ν(C=N) and ν(O-C-O) appears at 1567 cm-1 and

1461 cm-1 respectively

In the proton NMR spectrum of 1 the aliphatic protons of the bridging ethane

moiety resonates as a multiplet between 469 and 439 ppm see Fig S6 A broad

singlet at 1091 ppm corresponds to the protons of the amino nitrogens of 1 but the

analogous protons were observed as two broad signals in the proton NMR spectrum

of the free-ligand chret see Fig S5 For 1 the aromatic protons of the chromone

moieties and the imino signal coalesce into two multiplets (viz 895 ndash 865 ppm and

812 ndash 711 ppm) in comparison to the corresponding well-resolved signals at 872

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ppm (for the imino protons) and 798 767 737 ppm (for the aromatic protons of the

chromone moieties) of the free-ligand chret The most intense signal in the 1H NMR

spectrum of 2 is due to the H1 proton positioned on the chromone moiety which

appears as a sharp singlet (at 969 ppm)

The benzimidazole proton in 2 resonates as an intense signal at 939 ppm

which integrates to one while the multiplet between 827 and 722 ppm are due to

the remaining aromatic peaks The presence of the pi-conjugated neutral chelators in

1 and 2 results in the occurrence of only intra-ligand - transitions in their UV-Vis

spectra see Figs S7 and S8 As expected no metal-based d-d transitions are

observed at more red-shifted regions due to the low-spin d6 electron configurations

of 1 and 2

32 Crystal structure of 1

Compound 1 co-crystallized with three tetrahydrofuran molecules of

recrystallization in its triclinic unit cell The crystal lattice of 1 is stabilized by a

network of classical intramolecular [Br1H4a-N4 = 273(4) Aring and Br2H2a-N2 =

260(4) Aring] and intermolecular hydrogen bonding [O11AH2b-N2 = 195(4) Aring and

O11BH4b-N4 = 191(5) Aring] see Fig S9 Collectively these hydrogen bonding

interactions allows molecules of 1 to pack in columns parallel to the [a]- and [b]-axes

The metal centres of 1 are positioned in the centre of the distorted

octahedrons which are largely imposed on by their constrained bite angles [O1-Re1-

N1 = 8452(7)ordm and N3-Re2-O6 = 8393(7)ordm] see Fig 2 Consequently the C2-Re1-Br1

[17685(8)ordm] O1-Re1-C3 [17741(9)ordm] C1-Re1-N1 [1762(1)ordm] Br2-Re2-C6 [17699(8)ordm]

C4-Re2-O6 [17641(9)ordm] and N3-Re2-C5 [1742(1)ordm] deviate all from linearity The

flexibility of the bridging ethane moiety affords narrower C=N-C [C18-N3-C19 =

1148(2)ordm and C16-N1-C17 = 1150(2)ordm] bond angles than the expected 120ordm for a bond

angle containing a central sp2 hybridized nitrogen Despite the influence of the

bridging ethane moiety the imino bonds [C16-N1 = 1286(4) Aring and C19-N3 =

1291(4) Aring] of 1 are in the range [1285(3) - 1312(6) Aring] observed for similar bonds

found in other Schiff bases [7 11 21 22 23] Across the respective octahedrons only

the Re1-C2 [1894(3) Aring] and Re2-C6 [1893(3) Aring] bonds are nearly equidistant which

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reflects similar trans-influence induced by the Br1 and Br2 atoms respectively

Hence the comparable cis-orientated organometallic bonds [Re1-C1 = 1942(3) Aring

Re1-C3 = 1897(3) Aring Re2-C4 = 1908(3) Aring and Re2-C5 = 1932(3) Aring] across the

octahedrons in 1 differs

The rhenium to ketonic [Re1-O1 = 2137(2) Aring and Re2-O6 = 2139(2) Aring] and

imino nitrogen [Re1-N1 = 2169(2) Aring and Re2-N3 = 2171(2) Aring] bonds are similar to

analogous bonds found within fac-[Re(CO)3(chrpychr)Br] (chrpychr = 2-(4-oxo-4H-

chromen-3-yl)-5H-chromeno[23-d]pyrimidin-5-one) and [(micro-O)ReOCl(amp)2]

(amp= 6-amino-3-methyl-1-phenyl-4-azahept-2-ene-1-one) [24 25] Bond orders with

the chret chelator is established based on the ketonic bonds [C14-O1 = 1259(4) Aring and

C28-O6 = 1261(3) Aring] being longer than the carbonyl bonds [eg C1-O3 = 1144(3) Aring]

but yet shorter than the ether bonds [eg C8-O2 = 1383(3) Aring and C21-O7 = 1347(4)

Aring] Also the localized C=C bonds in the chromone moeities remain intact after

coordination of the chret chelators as these C=C bonds [C7-C15 = 1414(4) Aring and

C20-C21 = 1411(4) Aring] are shorter than the C-C single bond [C17-C18 = 1537(3) Aring]

that constitutes the bridging ethane moeity

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Fig 2 An ORTEP view of compound 1 showing 50 probability displacement ellipsoids

and the atom labelling The tetrahydrofuran molecules of crystallization were omitted for

clarity

33 Crystal structure of 2

Four molecules of 2 occupies its monoclinic unit cell and each of these

molecules forms dimers with molecules of 2 in adjacent unit cells via classical

hydrogen-bonding interactions [Br1N2A-H2ABr1AN2-H = 257(3) Aring] see Fig

S10 Consequently molecules of 2 are self-assembled in columns aligned with the

[b]-axis Indicative to 1 the constrained bite angle [O1-Re-N1 = 8199(7)ordm] of 2 results

in the deviation of orthogonality in the opposing C17-Re-C19 [8690(1)ordm] bond angle

see Fig 3

The rhenium to halide bonds of 1 [Re1-Br1 = 26455(3) Aring and Re2-Br2 =

26377(3) Aring] and 2 [Re-Br = 26322(8) Aring] are comparable to those found in other facial

tricarbonyl rhenium complexes [26 27] All the remaining coordination bonds of 2

[Re-N1 = 2186(2) Aring Re-O1 = 2141(1) Aring Re-C17 = 1931(2) Aring Re-C18 = 1901(2) Aring

and Re-C19 = 1901(2) Aring] were similar to its chloro-analogue fac-[Re(CO)3(bzch)Cl]

viz Re-Oketone = 2137(2) Aring Re-Nbenzimidazole = 2179(2) Aring and Re-Ccarbonyl = 1929(2) Aring

1904(2) Aring 1898(2) Aring [11] Furthermore the double bond character of the C10-N1

bonds [1336(3) Aring] are clearly established when compared to the C-N bond lengths

[C10-N2 = 1358(3) Aring C16-N1 = 1401(3) Aring and C11-N2 = 1374(3) Aring] In addition the

bridging C9-C10 [1466(3) Aring] bond is single based on the more shorter localized C=C

[1365(3) Aring] chromone bond In turn the degrees of freedom around the C9-10 single

bond allows the chromone and benzimidazole plane to form a dihedral angle of

601ordm Also the benzimidazole and chromone moeities lies out of the plane of the

O1N1C19C17 mean basal plane by 1783ordm and 1837ordm respectively The toluene

molecule of recrystallization from an adjacent unit cell is nearly co-planar with the

bzch chelator of 1 indicating - interactions between this toluene molecule and the

bzch chelator (toluene Csp2 centroid to C9 = 3309 Aring and toluene Csp2 centroid to C10

= 3561 Aring)

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An evaluation of the experimental and optimized geometrical parameters for

the metal complexes reveals that the calculated intraligand bond distances [C17-C18

= 15374 Aring for 1 and C1-C9 = 13601 Aring for 2] and angles [O6-Re2-N3 = 83023ordm for 1

and O1-Re-N1 = 80800ordm for 2] compares well with their analogous experimental

geometrical parameters [C17-C18 = 1537(4) Aring for 1 C1-C9 = 1365(3) Aring for 2 O6-

Re2-N3 = 8393(7)ordm for 1 and O1-Re-N1 = 8199(7)ordm for 2] In addition the differences

in bond lengths found between comparable experimental [eg Re1-C1 = 1942(3) Aring

for 1 and Re-C19 = 1901(2) Aring] and optimized [eg Re1-C1 = 19344 Aring for 1 and Re-

C19 = 19034 Aring for 2] organometallic Re-CO bonds are not significant Discrepencies

found between the experimental [Re1-Br1 = 26455(3) Aring Re2-Br2 = 26377(3) Aring for 1

and Re-Br = 26322(8) Aring for 2] and calculated [Re1-Br1 = 272064 Aring Re2-Br2 = 272059

Aring for 1 and Re-Br = 266556 Aring for 2] rhenium to halide bonds are significant which

are ascribed to the rhenium atoms having lower calculated Natural Population

Analysis charges (0851 for Re12 in 1 and 0889 in 2) than the formal +I charge [28

29] The same trend is observed when examining the Re-Oketonic and Re-N

coordination bonds which were found to be longer in the computational models [eg

Re1-O1 = 21765 Aring Re1-N1 = 22224 Aring for 1 and Re-O1 = 22226 Aring Re-N1 = 23072 Aring

for 2] due to their lower Lewis acidic character of the metal centres than those in the

crystal structures [eg Re1-O1 = 2137(2) Aring Re1-N1 = 2169(2) Aring for 1 and Re-O1 =

2141(2) Aring Re-N1 = 2186(2) Aring for 2]

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Fig 3 An ORTEP view of complex 2 showing 50 probability displacement ellipsoids and

the atom labelling The toluene molecule of crystallization was omitted for clarity

Conclusion

Exploring the coordination behaviours of the diimine chret and chb afforded the di-

and mononuclear rhenium(I) compounds fac-(Re(CO)3Br)2(micro-chret) (1) and fac-

[Re(CO)3(bzch)Br] (2) The interpretation of the IR experimental spectra of the metal

compounds was supported by their simulated spectra calculated at the DFT level of

theory X-ray studies concured with the spectroscopic characterization revealing the

transformation of the chb diimine into the bzch chelator (in 2) and affirming the

coordination modes of the chb (in 1) and bzch (in 2) chelators In addition the 6-

membered chelate rings had a significant influence on the geometrical parameters of

the octahedral geometries of 1 and 2

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Supporting information

CCDC 1451521 and 1451522 contains crystallographic data for this article These data

can be obtained free of charge at wwwccdccamacukcontsretrievinghtml [or

from the Cambridge Crystallographic Data Centre (CCDC) 12 Union Road

Cambridge CB21EZ UK Fax +44(0)1223-336033 Email depositccdccamacuk]

Supplementary figures S1-S10 associated with this article can be found in the online

version

Acknowledgements

We are grateful to the University of KwaZulu-Natal and the National Research

Foundation of South Africa for financial support

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Table 1 Crystal data and structure refinement data

13(C4H8O) 2C7H8

Chemical formula C28H18Br2N4O10Re23(C4H8O) C19H10BrN2O5ReC7H8

Formula weight 131899 70453

TemperatureK 100(2) 100(2)

Crystal system Triclinic Monoclinic

Space group P-1 P21n

Unit cell dimensions (Ǻ deg) a = 128859(6) a = 12400(5)

b = 131199(6) b = 11778(5)

c = 149558(7) c = 16316(5)

α= 114601(2) α = 90000(5)

β = 98138(2) β = 92469(5)

γ = 102350(2) γ = 90000(5)

Crystal size (mm) 013 x 006 x 005 009 x 006 x 005

V(Aring3) 216873 (18) 238007(16)

Z 2 4

Density (calc) (mgm3) 2020 1966

Absorption coefficient (mm-1) 749 682

F(000) 1268 1352

θ range for data collection

(deg)

16 291 20 290

Reflections measured 41497 23824

Observed reflections [Igt2σ(I)] 10414 5621

Independent reflections 11421 6310

DataRestraintsparameters 114210566 56210321

Goodness of fit on F2 103 103

Observed R wR2 0018 0043 0020 0042

Rint 0018 0027

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Table 2 Selected bond lengths [Aring] and bond angles [deg] for 1 The RMSD of 1 is 0720 Aring

Experimental Optimized

Re1-Br1 26455(3) 272064 Re2-Br2 26377(3) 272059 Re1-O1 2137(2) 21765 Re2-O6 2139(2) 21764 Re1-N1 2169(2) 22224 Re2-N3 2171(2) 22224 Re1-C1 1942(3) 19344 Re1-C2 1894(3) 19091 Re1-C3 1897(3) 19071 Re2-C4 1908(3) 19071 Re2-C5 1932(3) 19091 Re2-C6 1893(2) 19343 C16-N1 1286(4) 12919 C19-N3 1291(4) 12919 C14-O1 1259(4) 12502 C28-O6 1261(3) 12503 C1-O3 1144(3) 11492 C8-O2 1383(3) 13796 C21-O7 1347(4) 13440 C7-C15 1414(4) 14102 C20-C21 1411(4) 14103 C17-C18 1537(3) 15374 O1-Re1-N1 8452(7) 83027 O6-Re2-N3 8393(7) 83023 C2-Re1-Br1 17685(8) 177228 O1-Re1-C3 17741(9) 176550 C1-Re1-N1 1762(1) 174310 Br2-Re2-C6 17699(8) 177236 C4-Re2-O6 17641(9) 176545 N3-Re2-C5 1742(1) 174309 C16-N1-C17 1150(2) 114920 C18-N3-C19 1148(2) 114920

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Table 3 Selected bond lengths [Aring] and bond angles [deg] for 2 The RMSD of 2 is 0267 Aring

Experimental Optimized

Re-Br 26322(8) 266556 Re-N1 2186(2) 23072 Re-O1 2141(2) 22226 Re-C17 1931(2) 19263 Re-C18 1901(2) 19150 Re-C19 1901(2) 19034 C9-C10 1466(3) 14608 C1-C9 1365(3) 13601 O1-Re-N1 8199(7) 80800 C17-Re-C19 8690(1) 88380 Br-Re-C18 17582(7) 176266

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[6] RS Herrick TJ Brunker C Maus K Crandall A Cetin CJ

Ziegler Aqueous preparation and physiological stability studies of

Re(CO)3(tripodal) compounds Chem Commun (2006) 4330-4331

[7] K Potgieter P Mayer TIA Gerber IN Booysen Coordination behaviour of

the multidentate Schiff base 26-bis(2-hydroxyphenyliminomethyl)pyridine

towards the fac-[Re(CO)3]+ and [ReO]3+ cores Polyhedron 28 (2009) 2808-2812

[8] CL Ferreira CB Ewart SR Bayly B O Patrick J Steele MJ Adam C

Orvig Glucosamine Conjugates of Tricarbonylcyclopentadienyl Rhenium(I)

and Technetium(I) Cores Inorg Chem 45 (2006) 6979-6987

[9] Q Nadeem D Can Y Shen M Felber Z Mahmooda R Alberto Synthesis of

tripeptide derivatized cyclopentadienyl complexes of technetium and rhenium

as radiopharmaceutical probes Org Biomol Chem 12 (2014) 1966-1974

[10] IN Booysen M Ismail TIA Gerber M Akerman B Van Brecht Oxo and

oxofree rhenium(V) complexes with NO-donor Schiff bases S Afr J Chem 65

(2012) 174-177

[11] IN Booysen MB Ismail OQ Munro Mono- and dinuclear rhenium(I)

compounds with bidentate benzimidazole chelators Inorg Chem Commun 30

(2013) 168-172

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[12] IN Booysen MB Ismail MP Akerman Coordination behaviour of chromone

Schiff bases towards the [ReVO]3+ and [ReI(CO)3]+ cores J Coord Chem 66

(2013) 4371-4386

[13] S Bhatnagar S Sahir P Kackar S Kaushik MK Dave A Shukla A Goel

Synthesis and docking studies on styryl chromones exhibiting cytotoxicity in

human breast cancer cell line Bioorg Med Chem Lett 20 (2010) 4945-4950

[14] M Recanatini A Bisi A Cavalli F Belluti S Gobbi A Rampa P Valenti M

Palzer A Palusczak RW Hartmann A New Class of Nonsteroidal Aromatase

Inhibitorsthinsp Design and Synthesis of Chromone and Xanthone Derivatives and

Inhibition of the P450 Enzymes Aromatase and 17α-HydroxylaseC1720-

Lyase J Med Chem 44 (2001) 672-680

[15] IN Booysen A Adebisi MP Akerman OQ Munro B Xulu Coordination of

di- and triimine ligands at ruthenium(II) and ruthenium(III) centers structural

electrochemical and radical scavenging studies J Coord Chem (2016) doi

1010800095897220161177177

[16] Bruker APEX2 SAINT and SADABS Bruker AXS Inc (2010) Madison

Wisconsin USA

[17] RH Blessing An empirical correction for absorption anisotropy Acta Cryst

A51 (1995) 33-38

[18] GM Sheldrick A short history of SHELX Acta Cryst A64 (2008) 112-122

[19] LJ Farrugia WinGX and ORTEP for Windows an update J Appl Cryst 45

(2012) 849-854

[20] MJ Frisch GW Trucks HB Schlegel GE Scuseria MA Robb JR

Cheeseman G Scalmani V Barone B Mennucci GA Petersson H Nakatsuji

M Caricato X Li HP Hratchian AF Izmaylov J Bloino G Zheng JL

Sonnenberg M Hada M Ehara K Toyota R Fukuda J Hasegawa M Ishida

T Nakajima Y Honda O Kitao H Nakai T Vreven JA Montgomery Jr JE

Peralta F Ogliaro M Bearpark JJ Heyd E Brothers KN Kudin VN

Staroverov R Kobayashi J Normand K Raghavachari A Rendell JC

Burant SS Iyengar J Tomasi M Cossi N Rega JM Millam M Klene JE

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Knox JB Cross V Bakken C Adamo J Jaramillo R Gomperts RE

Stratmann O Yazyev AJ Austin R Cammi C Pomelli JW Ochterski RL

Martin K Morokuma VG Zakrzewski GA Voth P Salvador JJ

Dannenberg S Dapprich AD Daniels O Farkas JB Foresman JV Ortiz J

Cioslowski DJ Fox GAUSSIAN 09 (Revision A01) Gaussian

IncWallingford CT (2009)

[21] A Brink HG Visser A Roodt Novel imino rhenium(I) tricarbonyl complexes

of salicylidene-derived ligands Synthesis X-ray crystallographic studies

spectroscopic characterization and DFT calculations Polyhedron 52 (2013) 416-

423

[22] J Mukiza TIA Gerber EC Hosten Decarboxylation of 5-amino-orotic acid

and a Schiff base derivative by rhenium(V) Inorg Chem Comm 57 (2015) 54-

57

[23] K Potgieter P Mayer T Gerber N Yumata E Hosten I Booysen R Betz M

Ismail B van Brecht Rhenium(I) tricarbonyl complexes with multidentate

nitrogen-donor derivatives Polyhedron 49 (2013) 67-73

[24] IN Booysen I Ebinumoliseh MP Akerman B Xulu A rhenium(I) compound

bearing a dimerized chromone NO bidentate chelator Inorg Chem Comm 62

(2015) 8-10

[25] P Mayer TIA Gerber B Buyambo A Abrahams Coordination behaviour of

acetylacetone-derived Schiff bases towards rhenium(I) and (V) Polyhedron 28

(2009) 1174-1178

[26] T Jurca O Ramadan I Korobkov DS Richeson Employing sterically

encumbered bis(imino)pyridine ligands in support of fac-rhenium(I) carbonyls

J Organomet Chem 802 (2016) 27-31

[27] J Ho WY Lee KJT Koh PPF Lee YK Yan Rhenium(I) tricarbonyl

complexes of salicylaldehyde semicarbazones Synthesis crystal structures and

cytotoxicity J Inorg Biochem 119 (2013) 10-20

[28] B Machura A Świtlicka M Wolff J Kusz R Kruszynski Mono- and di-

nuclear oxorhenium(V) complexes of 47-diphenyl-110-phenanthroline

Polyhedron 28 (2009) 3999-4009

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[29] B Machura M Jaworska P Lodowski Natural bond orbital analysis and

density functional study of linear and bent oxo-bridged dimers of rhenium(V)

J Mol Struc-Theochem 766 (2006) 1-8

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Highlights

bull Chromone rhenium(I) compounds

bull Simulated IR spectra

bull Low calculated RMSDs

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non-hydrogen atoms were located in the difference density map and refined

anisotropically with SHELX-2014 [20] All hydrogen atoms were included as

idealised contributors in the least squares process Their positions were calculated

using a standard riding model with C-Haromatic distances of 093 Aring and Uiso = 12 Ueq

C-Hmethylene distances of 099 Aring and Uiso = 12 Ueq and CndashHmethyl distances of 098 Aring and

Uiso = 15 Ueq The amine hydrogen atoms were located in the difference density

map and allowed to refine isotropically

25 Computational details

Molecular simulations were conducted with GAUSSIAN 09W [20] Geometry

optimizations of 1 and 2 were achieved through a DFT calculation using the B3LYP

functional with an accompanying hybrid basis set viz the 6-311G++ (d p) basis set

was applied to all the C H N O and Br and the LANL2DZ basis set which makes

use of effective core potentials applied to the metal centre [12] Prior to the

calculation the solvent molecules of recrystallization for the respective metal

complexes were omitted from their crystal structures and the resultant structures

were used as the starting conformers Good agreement was found between the

optimized and experimental geometrical parameters (refer to Tables 2 and 3) with

the minor deviations attributed to the fact that the gas phase optimized structures do

not account for intermolecular interactions or any short distance contacts The close

correlation between the optimized and geometrical parameters of the respective

complexes is further emphasized by the low calculated root-mean-square deviation

(RMSD) see Fig 1 The larger RMSD of 1 is mainly ascribed to the largely free

rotation of the C-C single bonds within the chret chelator Using the optimized

structure of the metal complex the lack of any negative Eigen values in the

frequency calculations confirmed that the structures are at global minima on their

individual potential energy surfaces [21]

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Fig 1 Overlay structures of the optimized and experimental crystal structures for the

respective complexes with their corresponding RMSD values The crystal structures are

shown in yellow while the optimized structures are given in blue

3 Results and Discussion

31 Synthesis spectral characterization and computational studies

The metallic compounds fac-(Re(CO)3Br)2(micro-chret) (1) and fac-

[Re(CO)3(bzch)Br] (2) [bzch = 2-benzimidazole-4H-chromen-4-one] were synthesized

under anaerobic conditions from the equimolar reaction of [Re(CO)5Br] with the

diimines chret and chb respectively In 1 the chret ligand bridges two fac-

[Re(CO)3Br] units while coordinating as a bidentate moiety to each metal centre via

its NiminoOketo donor sets Despite the use of anaerobic conditions X-ray studies of 2

revealed that the chb diimine underwent intraligand cyclization followed by the

hydrolysis of one of its imine bonds In fact the chloro rhenium(I) analogue fac-

[Re(CO)3(bzch)Cl] was similarly formed from the reaction of [Re(CO)5Cl] with the

Schiff base ligand 2-(2- aminophenyliminomethyl)-4H-chromen-4-one (H2pch) which

led to the transformation of the latter to a bzch moiety [11] However no

transformation of the diimine chb occured in the dinuclear ruthenium(III)

compound (micro-chb)[mer-RuCl3(PPh3)]2 where the neutral chb moiety bridges the two

cis-[RuIIICl3] cores via its ketonic oxygen and imino nitrogen atoms [15] In contrast

to 2rsquos centralized 1 2-((methylene)imino)-benzene moiety the flexible

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((imino)methylene)-12-ethane bridging moiety of 1 minimizes steric strain within its

chret chelator which effectively induces stability and prevents the transformation of

the chret ligand Furthermore compounds 1 and 2 exhibits good solubility in high

boiling point polar solvents including dimethylsulfoxide and dimethylformamide

while showing a relatively modest solubility in tetrahydrofuran and poor solubility

in chlorinated solvents such as chloroform The low molar conductivities [ΛM = 1693

and 2372 ohmcm2mol-1] of the metallic compounds indicates their neutrality in

DMSO

Broad vibrational bands are observed below 1700 cm-1 in the experimental IR

spectra of the metal complexes which could not be clearly assigned without the aid

of the simulated IR spectra of 1 and 2 see Figs S1 ndash S4 Both the experimental [2015

1871 cm-1 for 1 and 2] and simulated [2105 2018 2016 cm-1 for 1 and 2097 2017 1993

cm-1 for 2] IR spectra are dominated by the intense stretches of the carbonyl co-

ligands Similarly the ν(N-H) vibrations of 1 and 2 appear as weak intensity

vibrational bands in their respective simulated [3644 cm-1 for 1 and 3654 3289 cm-1

for 2] and experimental [2920 2850 cm-1 for 1 and 2915 cm-1 for 2] IR spectra The

simulated IR spectrum of 1 indicates distinctive vibrational bands associated with

the ketonic (at 1687 cm-1) imine (at 1567 cm-1) and ether (at 1469 cm-1) bonds

whereas the corresponding IR stretching frequencies can be found at 1655 cm-1 [for

ν(C=O)] 1464 cm-1 1615 [for ν(O-C-O)] and 1613 cm-1 [for ν(C=N)] in the

experimental IR spectrum of 1 Correlating the simulated IR spectrum of 2 with its

experimental IR spectrum revealed that the experimental vibrations for ν(C=O) are

found at 1628 and 1607 cm-1 while ν(C=N) and ν(O-C-O) appears at 1567 cm-1 and

1461 cm-1 respectively

In the proton NMR spectrum of 1 the aliphatic protons of the bridging ethane

moiety resonates as a multiplet between 469 and 439 ppm see Fig S6 A broad

singlet at 1091 ppm corresponds to the protons of the amino nitrogens of 1 but the

analogous protons were observed as two broad signals in the proton NMR spectrum

of the free-ligand chret see Fig S5 For 1 the aromatic protons of the chromone

moieties and the imino signal coalesce into two multiplets (viz 895 ndash 865 ppm and

812 ndash 711 ppm) in comparison to the corresponding well-resolved signals at 872

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ppm (for the imino protons) and 798 767 737 ppm (for the aromatic protons of the

chromone moieties) of the free-ligand chret The most intense signal in the 1H NMR

spectrum of 2 is due to the H1 proton positioned on the chromone moiety which

appears as a sharp singlet (at 969 ppm)

The benzimidazole proton in 2 resonates as an intense signal at 939 ppm

which integrates to one while the multiplet between 827 and 722 ppm are due to

the remaining aromatic peaks The presence of the pi-conjugated neutral chelators in

1 and 2 results in the occurrence of only intra-ligand - transitions in their UV-Vis

spectra see Figs S7 and S8 As expected no metal-based d-d transitions are

observed at more red-shifted regions due to the low-spin d6 electron configurations

of 1 and 2

32 Crystal structure of 1

Compound 1 co-crystallized with three tetrahydrofuran molecules of

recrystallization in its triclinic unit cell The crystal lattice of 1 is stabilized by a

network of classical intramolecular [Br1H4a-N4 = 273(4) Aring and Br2H2a-N2 =

260(4) Aring] and intermolecular hydrogen bonding [O11AH2b-N2 = 195(4) Aring and

O11BH4b-N4 = 191(5) Aring] see Fig S9 Collectively these hydrogen bonding

interactions allows molecules of 1 to pack in columns parallel to the [a]- and [b]-axes

The metal centres of 1 are positioned in the centre of the distorted

octahedrons which are largely imposed on by their constrained bite angles [O1-Re1-

N1 = 8452(7)ordm and N3-Re2-O6 = 8393(7)ordm] see Fig 2 Consequently the C2-Re1-Br1

[17685(8)ordm] O1-Re1-C3 [17741(9)ordm] C1-Re1-N1 [1762(1)ordm] Br2-Re2-C6 [17699(8)ordm]

C4-Re2-O6 [17641(9)ordm] and N3-Re2-C5 [1742(1)ordm] deviate all from linearity The

flexibility of the bridging ethane moiety affords narrower C=N-C [C18-N3-C19 =

1148(2)ordm and C16-N1-C17 = 1150(2)ordm] bond angles than the expected 120ordm for a bond

angle containing a central sp2 hybridized nitrogen Despite the influence of the

bridging ethane moiety the imino bonds [C16-N1 = 1286(4) Aring and C19-N3 =

1291(4) Aring] of 1 are in the range [1285(3) - 1312(6) Aring] observed for similar bonds

found in other Schiff bases [7 11 21 22 23] Across the respective octahedrons only

the Re1-C2 [1894(3) Aring] and Re2-C6 [1893(3) Aring] bonds are nearly equidistant which

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reflects similar trans-influence induced by the Br1 and Br2 atoms respectively

Hence the comparable cis-orientated organometallic bonds [Re1-C1 = 1942(3) Aring

Re1-C3 = 1897(3) Aring Re2-C4 = 1908(3) Aring and Re2-C5 = 1932(3) Aring] across the

octahedrons in 1 differs

The rhenium to ketonic [Re1-O1 = 2137(2) Aring and Re2-O6 = 2139(2) Aring] and

imino nitrogen [Re1-N1 = 2169(2) Aring and Re2-N3 = 2171(2) Aring] bonds are similar to

analogous bonds found within fac-[Re(CO)3(chrpychr)Br] (chrpychr = 2-(4-oxo-4H-

chromen-3-yl)-5H-chromeno[23-d]pyrimidin-5-one) and [(micro-O)ReOCl(amp)2]

(amp= 6-amino-3-methyl-1-phenyl-4-azahept-2-ene-1-one) [24 25] Bond orders with

the chret chelator is established based on the ketonic bonds [C14-O1 = 1259(4) Aring and

C28-O6 = 1261(3) Aring] being longer than the carbonyl bonds [eg C1-O3 = 1144(3) Aring]

but yet shorter than the ether bonds [eg C8-O2 = 1383(3) Aring and C21-O7 = 1347(4)

Aring] Also the localized C=C bonds in the chromone moeities remain intact after

coordination of the chret chelators as these C=C bonds [C7-C15 = 1414(4) Aring and

C20-C21 = 1411(4) Aring] are shorter than the C-C single bond [C17-C18 = 1537(3) Aring]

that constitutes the bridging ethane moeity

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Fig 2 An ORTEP view of compound 1 showing 50 probability displacement ellipsoids

and the atom labelling The tetrahydrofuran molecules of crystallization were omitted for

clarity

33 Crystal structure of 2

Four molecules of 2 occupies its monoclinic unit cell and each of these

molecules forms dimers with molecules of 2 in adjacent unit cells via classical

hydrogen-bonding interactions [Br1N2A-H2ABr1AN2-H = 257(3) Aring] see Fig

S10 Consequently molecules of 2 are self-assembled in columns aligned with the

[b]-axis Indicative to 1 the constrained bite angle [O1-Re-N1 = 8199(7)ordm] of 2 results

in the deviation of orthogonality in the opposing C17-Re-C19 [8690(1)ordm] bond angle

see Fig 3

The rhenium to halide bonds of 1 [Re1-Br1 = 26455(3) Aring and Re2-Br2 =

26377(3) Aring] and 2 [Re-Br = 26322(8) Aring] are comparable to those found in other facial

tricarbonyl rhenium complexes [26 27] All the remaining coordination bonds of 2

[Re-N1 = 2186(2) Aring Re-O1 = 2141(1) Aring Re-C17 = 1931(2) Aring Re-C18 = 1901(2) Aring

and Re-C19 = 1901(2) Aring] were similar to its chloro-analogue fac-[Re(CO)3(bzch)Cl]

viz Re-Oketone = 2137(2) Aring Re-Nbenzimidazole = 2179(2) Aring and Re-Ccarbonyl = 1929(2) Aring

1904(2) Aring 1898(2) Aring [11] Furthermore the double bond character of the C10-N1

bonds [1336(3) Aring] are clearly established when compared to the C-N bond lengths

[C10-N2 = 1358(3) Aring C16-N1 = 1401(3) Aring and C11-N2 = 1374(3) Aring] In addition the

bridging C9-C10 [1466(3) Aring] bond is single based on the more shorter localized C=C

[1365(3) Aring] chromone bond In turn the degrees of freedom around the C9-10 single

bond allows the chromone and benzimidazole plane to form a dihedral angle of

601ordm Also the benzimidazole and chromone moeities lies out of the plane of the

O1N1C19C17 mean basal plane by 1783ordm and 1837ordm respectively The toluene

molecule of recrystallization from an adjacent unit cell is nearly co-planar with the

bzch chelator of 1 indicating - interactions between this toluene molecule and the

bzch chelator (toluene Csp2 centroid to C9 = 3309 Aring and toluene Csp2 centroid to C10

= 3561 Aring)

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An evaluation of the experimental and optimized geometrical parameters for

the metal complexes reveals that the calculated intraligand bond distances [C17-C18

= 15374 Aring for 1 and C1-C9 = 13601 Aring for 2] and angles [O6-Re2-N3 = 83023ordm for 1

and O1-Re-N1 = 80800ordm for 2] compares well with their analogous experimental

geometrical parameters [C17-C18 = 1537(4) Aring for 1 C1-C9 = 1365(3) Aring for 2 O6-

Re2-N3 = 8393(7)ordm for 1 and O1-Re-N1 = 8199(7)ordm for 2] In addition the differences

in bond lengths found between comparable experimental [eg Re1-C1 = 1942(3) Aring

for 1 and Re-C19 = 1901(2) Aring] and optimized [eg Re1-C1 = 19344 Aring for 1 and Re-

C19 = 19034 Aring for 2] organometallic Re-CO bonds are not significant Discrepencies

found between the experimental [Re1-Br1 = 26455(3) Aring Re2-Br2 = 26377(3) Aring for 1

and Re-Br = 26322(8) Aring for 2] and calculated [Re1-Br1 = 272064 Aring Re2-Br2 = 272059

Aring for 1 and Re-Br = 266556 Aring for 2] rhenium to halide bonds are significant which

are ascribed to the rhenium atoms having lower calculated Natural Population

Analysis charges (0851 for Re12 in 1 and 0889 in 2) than the formal +I charge [28

29] The same trend is observed when examining the Re-Oketonic and Re-N

coordination bonds which were found to be longer in the computational models [eg

Re1-O1 = 21765 Aring Re1-N1 = 22224 Aring for 1 and Re-O1 = 22226 Aring Re-N1 = 23072 Aring

for 2] due to their lower Lewis acidic character of the metal centres than those in the

crystal structures [eg Re1-O1 = 2137(2) Aring Re1-N1 = 2169(2) Aring for 1 and Re-O1 =

2141(2) Aring Re-N1 = 2186(2) Aring for 2]

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Fig 3 An ORTEP view of complex 2 showing 50 probability displacement ellipsoids and

the atom labelling The toluene molecule of crystallization was omitted for clarity

Conclusion

Exploring the coordination behaviours of the diimine chret and chb afforded the di-

and mononuclear rhenium(I) compounds fac-(Re(CO)3Br)2(micro-chret) (1) and fac-

[Re(CO)3(bzch)Br] (2) The interpretation of the IR experimental spectra of the metal

compounds was supported by their simulated spectra calculated at the DFT level of

theory X-ray studies concured with the spectroscopic characterization revealing the

transformation of the chb diimine into the bzch chelator (in 2) and affirming the

coordination modes of the chb (in 1) and bzch (in 2) chelators In addition the 6-

membered chelate rings had a significant influence on the geometrical parameters of

the octahedral geometries of 1 and 2

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Supporting information

CCDC 1451521 and 1451522 contains crystallographic data for this article These data

can be obtained free of charge at wwwccdccamacukcontsretrievinghtml [or

from the Cambridge Crystallographic Data Centre (CCDC) 12 Union Road

Cambridge CB21EZ UK Fax +44(0)1223-336033 Email depositccdccamacuk]

Supplementary figures S1-S10 associated with this article can be found in the online

version

Acknowledgements

We are grateful to the University of KwaZulu-Natal and the National Research

Foundation of South Africa for financial support

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Table 1 Crystal data and structure refinement data

13(C4H8O) 2C7H8

Chemical formula C28H18Br2N4O10Re23(C4H8O) C19H10BrN2O5ReC7H8

Formula weight 131899 70453

TemperatureK 100(2) 100(2)

Crystal system Triclinic Monoclinic

Space group P-1 P21n

Unit cell dimensions (Ǻ deg) a = 128859(6) a = 12400(5)

b = 131199(6) b = 11778(5)

c = 149558(7) c = 16316(5)

α= 114601(2) α = 90000(5)

β = 98138(2) β = 92469(5)

γ = 102350(2) γ = 90000(5)

Crystal size (mm) 013 x 006 x 005 009 x 006 x 005

V(Aring3) 216873 (18) 238007(16)

Z 2 4

Density (calc) (mgm3) 2020 1966

Absorption coefficient (mm-1) 749 682

F(000) 1268 1352

θ range for data collection

(deg)

16 291 20 290

Reflections measured 41497 23824

Observed reflections [Igt2σ(I)] 10414 5621

Independent reflections 11421 6310

DataRestraintsparameters 114210566 56210321

Goodness of fit on F2 103 103

Observed R wR2 0018 0043 0020 0042

Rint 0018 0027

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Table 2 Selected bond lengths [Aring] and bond angles [deg] for 1 The RMSD of 1 is 0720 Aring

Experimental Optimized

Re1-Br1 26455(3) 272064 Re2-Br2 26377(3) 272059 Re1-O1 2137(2) 21765 Re2-O6 2139(2) 21764 Re1-N1 2169(2) 22224 Re2-N3 2171(2) 22224 Re1-C1 1942(3) 19344 Re1-C2 1894(3) 19091 Re1-C3 1897(3) 19071 Re2-C4 1908(3) 19071 Re2-C5 1932(3) 19091 Re2-C6 1893(2) 19343 C16-N1 1286(4) 12919 C19-N3 1291(4) 12919 C14-O1 1259(4) 12502 C28-O6 1261(3) 12503 C1-O3 1144(3) 11492 C8-O2 1383(3) 13796 C21-O7 1347(4) 13440 C7-C15 1414(4) 14102 C20-C21 1411(4) 14103 C17-C18 1537(3) 15374 O1-Re1-N1 8452(7) 83027 O6-Re2-N3 8393(7) 83023 C2-Re1-Br1 17685(8) 177228 O1-Re1-C3 17741(9) 176550 C1-Re1-N1 1762(1) 174310 Br2-Re2-C6 17699(8) 177236 C4-Re2-O6 17641(9) 176545 N3-Re2-C5 1742(1) 174309 C16-N1-C17 1150(2) 114920 C18-N3-C19 1148(2) 114920

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Table 3 Selected bond lengths [Aring] and bond angles [deg] for 2 The RMSD of 2 is 0267 Aring

Experimental Optimized

Re-Br 26322(8) 266556 Re-N1 2186(2) 23072 Re-O1 2141(2) 22226 Re-C17 1931(2) 19263 Re-C18 1901(2) 19150 Re-C19 1901(2) 19034 C9-C10 1466(3) 14608 C1-C9 1365(3) 13601 O1-Re-N1 8199(7) 80800 C17-Re-C19 8690(1) 88380 Br-Re-C18 17582(7) 176266

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Ziegler Aqueous preparation and physiological stability studies of

Re(CO)3(tripodal) compounds Chem Commun (2006) 4330-4331

[7] K Potgieter P Mayer TIA Gerber IN Booysen Coordination behaviour of

the multidentate Schiff base 26-bis(2-hydroxyphenyliminomethyl)pyridine

towards the fac-[Re(CO)3]+ and [ReO]3+ cores Polyhedron 28 (2009) 2808-2812

[8] CL Ferreira CB Ewart SR Bayly B O Patrick J Steele MJ Adam C

Orvig Glucosamine Conjugates of Tricarbonylcyclopentadienyl Rhenium(I)

and Technetium(I) Cores Inorg Chem 45 (2006) 6979-6987

[9] Q Nadeem D Can Y Shen M Felber Z Mahmooda R Alberto Synthesis of

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as radiopharmaceutical probes Org Biomol Chem 12 (2014) 1966-1974

[10] IN Booysen M Ismail TIA Gerber M Akerman B Van Brecht Oxo and

oxofree rhenium(V) complexes with NO-donor Schiff bases S Afr J Chem 65

(2012) 174-177

[11] IN Booysen MB Ismail OQ Munro Mono- and dinuclear rhenium(I)

compounds with bidentate benzimidazole chelators Inorg Chem Commun 30

(2013) 168-172

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[12] IN Booysen MB Ismail MP Akerman Coordination behaviour of chromone

Schiff bases towards the [ReVO]3+ and [ReI(CO)3]+ cores J Coord Chem 66

(2013) 4371-4386

[13] S Bhatnagar S Sahir P Kackar S Kaushik MK Dave A Shukla A Goel

Synthesis and docking studies on styryl chromones exhibiting cytotoxicity in

human breast cancer cell line Bioorg Med Chem Lett 20 (2010) 4945-4950

[14] M Recanatini A Bisi A Cavalli F Belluti S Gobbi A Rampa P Valenti M

Palzer A Palusczak RW Hartmann A New Class of Nonsteroidal Aromatase

Inhibitorsthinsp Design and Synthesis of Chromone and Xanthone Derivatives and

Inhibition of the P450 Enzymes Aromatase and 17α-HydroxylaseC1720-

Lyase J Med Chem 44 (2001) 672-680

[15] IN Booysen A Adebisi MP Akerman OQ Munro B Xulu Coordination of

di- and triimine ligands at ruthenium(II) and ruthenium(III) centers structural

electrochemical and radical scavenging studies J Coord Chem (2016) doi

1010800095897220161177177

[16] Bruker APEX2 SAINT and SADABS Bruker AXS Inc (2010) Madison

Wisconsin USA

[17] RH Blessing An empirical correction for absorption anisotropy Acta Cryst

A51 (1995) 33-38

[18] GM Sheldrick A short history of SHELX Acta Cryst A64 (2008) 112-122

[19] LJ Farrugia WinGX and ORTEP for Windows an update J Appl Cryst 45

(2012) 849-854

[20] MJ Frisch GW Trucks HB Schlegel GE Scuseria MA Robb JR

Cheeseman G Scalmani V Barone B Mennucci GA Petersson H Nakatsuji

M Caricato X Li HP Hratchian AF Izmaylov J Bloino G Zheng JL

Sonnenberg M Hada M Ehara K Toyota R Fukuda J Hasegawa M Ishida

T Nakajima Y Honda O Kitao H Nakai T Vreven JA Montgomery Jr JE

Peralta F Ogliaro M Bearpark JJ Heyd E Brothers KN Kudin VN

Staroverov R Kobayashi J Normand K Raghavachari A Rendell JC

Burant SS Iyengar J Tomasi M Cossi N Rega JM Millam M Klene JE

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Knox JB Cross V Bakken C Adamo J Jaramillo R Gomperts RE

Stratmann O Yazyev AJ Austin R Cammi C Pomelli JW Ochterski RL

Martin K Morokuma VG Zakrzewski GA Voth P Salvador JJ

Dannenberg S Dapprich AD Daniels O Farkas JB Foresman JV Ortiz J

Cioslowski DJ Fox GAUSSIAN 09 (Revision A01) Gaussian

IncWallingford CT (2009)

[21] A Brink HG Visser A Roodt Novel imino rhenium(I) tricarbonyl complexes

of salicylidene-derived ligands Synthesis X-ray crystallographic studies

spectroscopic characterization and DFT calculations Polyhedron 52 (2013) 416-

423

[22] J Mukiza TIA Gerber EC Hosten Decarboxylation of 5-amino-orotic acid

and a Schiff base derivative by rhenium(V) Inorg Chem Comm 57 (2015) 54-

57

[23] K Potgieter P Mayer T Gerber N Yumata E Hosten I Booysen R Betz M

Ismail B van Brecht Rhenium(I) tricarbonyl complexes with multidentate

nitrogen-donor derivatives Polyhedron 49 (2013) 67-73

[24] IN Booysen I Ebinumoliseh MP Akerman B Xulu A rhenium(I) compound

bearing a dimerized chromone NO bidentate chelator Inorg Chem Comm 62

(2015) 8-10

[25] P Mayer TIA Gerber B Buyambo A Abrahams Coordination behaviour of

acetylacetone-derived Schiff bases towards rhenium(I) and (V) Polyhedron 28

(2009) 1174-1178

[26] T Jurca O Ramadan I Korobkov DS Richeson Employing sterically

encumbered bis(imino)pyridine ligands in support of fac-rhenium(I) carbonyls

J Organomet Chem 802 (2016) 27-31

[27] J Ho WY Lee KJT Koh PPF Lee YK Yan Rhenium(I) tricarbonyl

complexes of salicylaldehyde semicarbazones Synthesis crystal structures and

cytotoxicity J Inorg Biochem 119 (2013) 10-20

[28] B Machura A Świtlicka M Wolff J Kusz R Kruszynski Mono- and di-

nuclear oxorhenium(V) complexes of 47-diphenyl-110-phenanthroline

Polyhedron 28 (2009) 3999-4009

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[29] B Machura M Jaworska P Lodowski Natural bond orbital analysis and

density functional study of linear and bent oxo-bridged dimers of rhenium(V)

J Mol Struc-Theochem 766 (2006) 1-8

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Highlights

bull Chromone rhenium(I) compounds

bull Simulated IR spectra

bull Low calculated RMSDs

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Fig 1 Overlay structures of the optimized and experimental crystal structures for the

respective complexes with their corresponding RMSD values The crystal structures are

shown in yellow while the optimized structures are given in blue

3 Results and Discussion

31 Synthesis spectral characterization and computational studies

The metallic compounds fac-(Re(CO)3Br)2(micro-chret) (1) and fac-

[Re(CO)3(bzch)Br] (2) [bzch = 2-benzimidazole-4H-chromen-4-one] were synthesized

under anaerobic conditions from the equimolar reaction of [Re(CO)5Br] with the

diimines chret and chb respectively In 1 the chret ligand bridges two fac-

[Re(CO)3Br] units while coordinating as a bidentate moiety to each metal centre via

its NiminoOketo donor sets Despite the use of anaerobic conditions X-ray studies of 2

revealed that the chb diimine underwent intraligand cyclization followed by the

hydrolysis of one of its imine bonds In fact the chloro rhenium(I) analogue fac-

[Re(CO)3(bzch)Cl] was similarly formed from the reaction of [Re(CO)5Cl] with the

Schiff base ligand 2-(2- aminophenyliminomethyl)-4H-chromen-4-one (H2pch) which

led to the transformation of the latter to a bzch moiety [11] However no

transformation of the diimine chb occured in the dinuclear ruthenium(III)

compound (micro-chb)[mer-RuCl3(PPh3)]2 where the neutral chb moiety bridges the two

cis-[RuIIICl3] cores via its ketonic oxygen and imino nitrogen atoms [15] In contrast

to 2rsquos centralized 1 2-((methylene)imino)-benzene moiety the flexible

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((imino)methylene)-12-ethane bridging moiety of 1 minimizes steric strain within its

chret chelator which effectively induces stability and prevents the transformation of

the chret ligand Furthermore compounds 1 and 2 exhibits good solubility in high

boiling point polar solvents including dimethylsulfoxide and dimethylformamide

while showing a relatively modest solubility in tetrahydrofuran and poor solubility

in chlorinated solvents such as chloroform The low molar conductivities [ΛM = 1693

and 2372 ohmcm2mol-1] of the metallic compounds indicates their neutrality in

DMSO

Broad vibrational bands are observed below 1700 cm-1 in the experimental IR

spectra of the metal complexes which could not be clearly assigned without the aid

of the simulated IR spectra of 1 and 2 see Figs S1 ndash S4 Both the experimental [2015

1871 cm-1 for 1 and 2] and simulated [2105 2018 2016 cm-1 for 1 and 2097 2017 1993

cm-1 for 2] IR spectra are dominated by the intense stretches of the carbonyl co-

ligands Similarly the ν(N-H) vibrations of 1 and 2 appear as weak intensity

vibrational bands in their respective simulated [3644 cm-1 for 1 and 3654 3289 cm-1

for 2] and experimental [2920 2850 cm-1 for 1 and 2915 cm-1 for 2] IR spectra The

simulated IR spectrum of 1 indicates distinctive vibrational bands associated with

the ketonic (at 1687 cm-1) imine (at 1567 cm-1) and ether (at 1469 cm-1) bonds

whereas the corresponding IR stretching frequencies can be found at 1655 cm-1 [for

ν(C=O)] 1464 cm-1 1615 [for ν(O-C-O)] and 1613 cm-1 [for ν(C=N)] in the

experimental IR spectrum of 1 Correlating the simulated IR spectrum of 2 with its

experimental IR spectrum revealed that the experimental vibrations for ν(C=O) are

found at 1628 and 1607 cm-1 while ν(C=N) and ν(O-C-O) appears at 1567 cm-1 and

1461 cm-1 respectively

In the proton NMR spectrum of 1 the aliphatic protons of the bridging ethane

moiety resonates as a multiplet between 469 and 439 ppm see Fig S6 A broad

singlet at 1091 ppm corresponds to the protons of the amino nitrogens of 1 but the

analogous protons were observed as two broad signals in the proton NMR spectrum

of the free-ligand chret see Fig S5 For 1 the aromatic protons of the chromone

moieties and the imino signal coalesce into two multiplets (viz 895 ndash 865 ppm and

812 ndash 711 ppm) in comparison to the corresponding well-resolved signals at 872

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ppm (for the imino protons) and 798 767 737 ppm (for the aromatic protons of the

chromone moieties) of the free-ligand chret The most intense signal in the 1H NMR

spectrum of 2 is due to the H1 proton positioned on the chromone moiety which

appears as a sharp singlet (at 969 ppm)

The benzimidazole proton in 2 resonates as an intense signal at 939 ppm

which integrates to one while the multiplet between 827 and 722 ppm are due to

the remaining aromatic peaks The presence of the pi-conjugated neutral chelators in

1 and 2 results in the occurrence of only intra-ligand - transitions in their UV-Vis

spectra see Figs S7 and S8 As expected no metal-based d-d transitions are

observed at more red-shifted regions due to the low-spin d6 electron configurations

of 1 and 2

32 Crystal structure of 1

Compound 1 co-crystallized with three tetrahydrofuran molecules of

recrystallization in its triclinic unit cell The crystal lattice of 1 is stabilized by a

network of classical intramolecular [Br1H4a-N4 = 273(4) Aring and Br2H2a-N2 =

260(4) Aring] and intermolecular hydrogen bonding [O11AH2b-N2 = 195(4) Aring and

O11BH4b-N4 = 191(5) Aring] see Fig S9 Collectively these hydrogen bonding

interactions allows molecules of 1 to pack in columns parallel to the [a]- and [b]-axes

The metal centres of 1 are positioned in the centre of the distorted

octahedrons which are largely imposed on by their constrained bite angles [O1-Re1-

N1 = 8452(7)ordm and N3-Re2-O6 = 8393(7)ordm] see Fig 2 Consequently the C2-Re1-Br1

[17685(8)ordm] O1-Re1-C3 [17741(9)ordm] C1-Re1-N1 [1762(1)ordm] Br2-Re2-C6 [17699(8)ordm]

C4-Re2-O6 [17641(9)ordm] and N3-Re2-C5 [1742(1)ordm] deviate all from linearity The

flexibility of the bridging ethane moiety affords narrower C=N-C [C18-N3-C19 =

1148(2)ordm and C16-N1-C17 = 1150(2)ordm] bond angles than the expected 120ordm for a bond

angle containing a central sp2 hybridized nitrogen Despite the influence of the

bridging ethane moiety the imino bonds [C16-N1 = 1286(4) Aring and C19-N3 =

1291(4) Aring] of 1 are in the range [1285(3) - 1312(6) Aring] observed for similar bonds

found in other Schiff bases [7 11 21 22 23] Across the respective octahedrons only

the Re1-C2 [1894(3) Aring] and Re2-C6 [1893(3) Aring] bonds are nearly equidistant which

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reflects similar trans-influence induced by the Br1 and Br2 atoms respectively

Hence the comparable cis-orientated organometallic bonds [Re1-C1 = 1942(3) Aring

Re1-C3 = 1897(3) Aring Re2-C4 = 1908(3) Aring and Re2-C5 = 1932(3) Aring] across the

octahedrons in 1 differs

The rhenium to ketonic [Re1-O1 = 2137(2) Aring and Re2-O6 = 2139(2) Aring] and

imino nitrogen [Re1-N1 = 2169(2) Aring and Re2-N3 = 2171(2) Aring] bonds are similar to

analogous bonds found within fac-[Re(CO)3(chrpychr)Br] (chrpychr = 2-(4-oxo-4H-

chromen-3-yl)-5H-chromeno[23-d]pyrimidin-5-one) and [(micro-O)ReOCl(amp)2]

(amp= 6-amino-3-methyl-1-phenyl-4-azahept-2-ene-1-one) [24 25] Bond orders with

the chret chelator is established based on the ketonic bonds [C14-O1 = 1259(4) Aring and

C28-O6 = 1261(3) Aring] being longer than the carbonyl bonds [eg C1-O3 = 1144(3) Aring]

but yet shorter than the ether bonds [eg C8-O2 = 1383(3) Aring and C21-O7 = 1347(4)

Aring] Also the localized C=C bonds in the chromone moeities remain intact after

coordination of the chret chelators as these C=C bonds [C7-C15 = 1414(4) Aring and

C20-C21 = 1411(4) Aring] are shorter than the C-C single bond [C17-C18 = 1537(3) Aring]

that constitutes the bridging ethane moeity

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Fig 2 An ORTEP view of compound 1 showing 50 probability displacement ellipsoids

and the atom labelling The tetrahydrofuran molecules of crystallization were omitted for

clarity

33 Crystal structure of 2

Four molecules of 2 occupies its monoclinic unit cell and each of these

molecules forms dimers with molecules of 2 in adjacent unit cells via classical

hydrogen-bonding interactions [Br1N2A-H2ABr1AN2-H = 257(3) Aring] see Fig

S10 Consequently molecules of 2 are self-assembled in columns aligned with the

[b]-axis Indicative to 1 the constrained bite angle [O1-Re-N1 = 8199(7)ordm] of 2 results

in the deviation of orthogonality in the opposing C17-Re-C19 [8690(1)ordm] bond angle

see Fig 3

The rhenium to halide bonds of 1 [Re1-Br1 = 26455(3) Aring and Re2-Br2 =

26377(3) Aring] and 2 [Re-Br = 26322(8) Aring] are comparable to those found in other facial

tricarbonyl rhenium complexes [26 27] All the remaining coordination bonds of 2

[Re-N1 = 2186(2) Aring Re-O1 = 2141(1) Aring Re-C17 = 1931(2) Aring Re-C18 = 1901(2) Aring

and Re-C19 = 1901(2) Aring] were similar to its chloro-analogue fac-[Re(CO)3(bzch)Cl]

viz Re-Oketone = 2137(2) Aring Re-Nbenzimidazole = 2179(2) Aring and Re-Ccarbonyl = 1929(2) Aring

1904(2) Aring 1898(2) Aring [11] Furthermore the double bond character of the C10-N1

bonds [1336(3) Aring] are clearly established when compared to the C-N bond lengths

[C10-N2 = 1358(3) Aring C16-N1 = 1401(3) Aring and C11-N2 = 1374(3) Aring] In addition the

bridging C9-C10 [1466(3) Aring] bond is single based on the more shorter localized C=C

[1365(3) Aring] chromone bond In turn the degrees of freedom around the C9-10 single

bond allows the chromone and benzimidazole plane to form a dihedral angle of

601ordm Also the benzimidazole and chromone moeities lies out of the plane of the

O1N1C19C17 mean basal plane by 1783ordm and 1837ordm respectively The toluene

molecule of recrystallization from an adjacent unit cell is nearly co-planar with the

bzch chelator of 1 indicating - interactions between this toluene molecule and the

bzch chelator (toluene Csp2 centroid to C9 = 3309 Aring and toluene Csp2 centroid to C10

= 3561 Aring)

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An evaluation of the experimental and optimized geometrical parameters for

the metal complexes reveals that the calculated intraligand bond distances [C17-C18

= 15374 Aring for 1 and C1-C9 = 13601 Aring for 2] and angles [O6-Re2-N3 = 83023ordm for 1

and O1-Re-N1 = 80800ordm for 2] compares well with their analogous experimental

geometrical parameters [C17-C18 = 1537(4) Aring for 1 C1-C9 = 1365(3) Aring for 2 O6-

Re2-N3 = 8393(7)ordm for 1 and O1-Re-N1 = 8199(7)ordm for 2] In addition the differences

in bond lengths found between comparable experimental [eg Re1-C1 = 1942(3) Aring

for 1 and Re-C19 = 1901(2) Aring] and optimized [eg Re1-C1 = 19344 Aring for 1 and Re-

C19 = 19034 Aring for 2] organometallic Re-CO bonds are not significant Discrepencies

found between the experimental [Re1-Br1 = 26455(3) Aring Re2-Br2 = 26377(3) Aring for 1

and Re-Br = 26322(8) Aring for 2] and calculated [Re1-Br1 = 272064 Aring Re2-Br2 = 272059

Aring for 1 and Re-Br = 266556 Aring for 2] rhenium to halide bonds are significant which

are ascribed to the rhenium atoms having lower calculated Natural Population

Analysis charges (0851 for Re12 in 1 and 0889 in 2) than the formal +I charge [28

29] The same trend is observed when examining the Re-Oketonic and Re-N

coordination bonds which were found to be longer in the computational models [eg

Re1-O1 = 21765 Aring Re1-N1 = 22224 Aring for 1 and Re-O1 = 22226 Aring Re-N1 = 23072 Aring

for 2] due to their lower Lewis acidic character of the metal centres than those in the

crystal structures [eg Re1-O1 = 2137(2) Aring Re1-N1 = 2169(2) Aring for 1 and Re-O1 =

2141(2) Aring Re-N1 = 2186(2) Aring for 2]

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Fig 3 An ORTEP view of complex 2 showing 50 probability displacement ellipsoids and

the atom labelling The toluene molecule of crystallization was omitted for clarity

Conclusion

Exploring the coordination behaviours of the diimine chret and chb afforded the di-

and mononuclear rhenium(I) compounds fac-(Re(CO)3Br)2(micro-chret) (1) and fac-

[Re(CO)3(bzch)Br] (2) The interpretation of the IR experimental spectra of the metal

compounds was supported by their simulated spectra calculated at the DFT level of

theory X-ray studies concured with the spectroscopic characterization revealing the

transformation of the chb diimine into the bzch chelator (in 2) and affirming the

coordination modes of the chb (in 1) and bzch (in 2) chelators In addition the 6-

membered chelate rings had a significant influence on the geometrical parameters of

the octahedral geometries of 1 and 2

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Supporting information

CCDC 1451521 and 1451522 contains crystallographic data for this article These data

can be obtained free of charge at wwwccdccamacukcontsretrievinghtml [or

from the Cambridge Crystallographic Data Centre (CCDC) 12 Union Road

Cambridge CB21EZ UK Fax +44(0)1223-336033 Email depositccdccamacuk]

Supplementary figures S1-S10 associated with this article can be found in the online

version

Acknowledgements

We are grateful to the University of KwaZulu-Natal and the National Research

Foundation of South Africa for financial support

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Table 1 Crystal data and structure refinement data

13(C4H8O) 2C7H8

Chemical formula C28H18Br2N4O10Re23(C4H8O) C19H10BrN2O5ReC7H8

Formula weight 131899 70453

TemperatureK 100(2) 100(2)

Crystal system Triclinic Monoclinic

Space group P-1 P21n

Unit cell dimensions (Ǻ deg) a = 128859(6) a = 12400(5)

b = 131199(6) b = 11778(5)

c = 149558(7) c = 16316(5)

α= 114601(2) α = 90000(5)

β = 98138(2) β = 92469(5)

γ = 102350(2) γ = 90000(5)

Crystal size (mm) 013 x 006 x 005 009 x 006 x 005

V(Aring3) 216873 (18) 238007(16)

Z 2 4

Density (calc) (mgm3) 2020 1966

Absorption coefficient (mm-1) 749 682

F(000) 1268 1352

θ range for data collection

(deg)

16 291 20 290

Reflections measured 41497 23824

Observed reflections [Igt2σ(I)] 10414 5621

Independent reflections 11421 6310

DataRestraintsparameters 114210566 56210321

Goodness of fit on F2 103 103

Observed R wR2 0018 0043 0020 0042

Rint 0018 0027

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Table 2 Selected bond lengths [Aring] and bond angles [deg] for 1 The RMSD of 1 is 0720 Aring

Experimental Optimized

Re1-Br1 26455(3) 272064 Re2-Br2 26377(3) 272059 Re1-O1 2137(2) 21765 Re2-O6 2139(2) 21764 Re1-N1 2169(2) 22224 Re2-N3 2171(2) 22224 Re1-C1 1942(3) 19344 Re1-C2 1894(3) 19091 Re1-C3 1897(3) 19071 Re2-C4 1908(3) 19071 Re2-C5 1932(3) 19091 Re2-C6 1893(2) 19343 C16-N1 1286(4) 12919 C19-N3 1291(4) 12919 C14-O1 1259(4) 12502 C28-O6 1261(3) 12503 C1-O3 1144(3) 11492 C8-O2 1383(3) 13796 C21-O7 1347(4) 13440 C7-C15 1414(4) 14102 C20-C21 1411(4) 14103 C17-C18 1537(3) 15374 O1-Re1-N1 8452(7) 83027 O6-Re2-N3 8393(7) 83023 C2-Re1-Br1 17685(8) 177228 O1-Re1-C3 17741(9) 176550 C1-Re1-N1 1762(1) 174310 Br2-Re2-C6 17699(8) 177236 C4-Re2-O6 17641(9) 176545 N3-Re2-C5 1742(1) 174309 C16-N1-C17 1150(2) 114920 C18-N3-C19 1148(2) 114920

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Table 3 Selected bond lengths [Aring] and bond angles [deg] for 2 The RMSD of 2 is 0267 Aring

Experimental Optimized

Re-Br 26322(8) 266556 Re-N1 2186(2) 23072 Re-O1 2141(2) 22226 Re-C17 1931(2) 19263 Re-C18 1901(2) 19150 Re-C19 1901(2) 19034 C9-C10 1466(3) 14608 C1-C9 1365(3) 13601 O1-Re-N1 8199(7) 80800 C17-Re-C19 8690(1) 88380 Br-Re-C18 17582(7) 176266

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[12] IN Booysen MB Ismail MP Akerman Coordination behaviour of chromone

Schiff bases towards the [ReVO]3+ and [ReI(CO)3]+ cores J Coord Chem 66

(2013) 4371-4386

[13] S Bhatnagar S Sahir P Kackar S Kaushik MK Dave A Shukla A Goel

Synthesis and docking studies on styryl chromones exhibiting cytotoxicity in

human breast cancer cell line Bioorg Med Chem Lett 20 (2010) 4945-4950

[14] M Recanatini A Bisi A Cavalli F Belluti S Gobbi A Rampa P Valenti M

Palzer A Palusczak RW Hartmann A New Class of Nonsteroidal Aromatase

Inhibitorsthinsp Design and Synthesis of Chromone and Xanthone Derivatives and

Inhibition of the P450 Enzymes Aromatase and 17α-HydroxylaseC1720-

Lyase J Med Chem 44 (2001) 672-680

[15] IN Booysen A Adebisi MP Akerman OQ Munro B Xulu Coordination of

di- and triimine ligands at ruthenium(II) and ruthenium(III) centers structural

electrochemical and radical scavenging studies J Coord Chem (2016) doi

1010800095897220161177177

[16] Bruker APEX2 SAINT and SADABS Bruker AXS Inc (2010) Madison

Wisconsin USA

[17] RH Blessing An empirical correction for absorption anisotropy Acta Cryst

A51 (1995) 33-38

[18] GM Sheldrick A short history of SHELX Acta Cryst A64 (2008) 112-122

[19] LJ Farrugia WinGX and ORTEP for Windows an update J Appl Cryst 45

(2012) 849-854

[20] MJ Frisch GW Trucks HB Schlegel GE Scuseria MA Robb JR

Cheeseman G Scalmani V Barone B Mennucci GA Petersson H Nakatsuji

M Caricato X Li HP Hratchian AF Izmaylov J Bloino G Zheng JL

Sonnenberg M Hada M Ehara K Toyota R Fukuda J Hasegawa M Ishida

T Nakajima Y Honda O Kitao H Nakai T Vreven JA Montgomery Jr JE

Peralta F Ogliaro M Bearpark JJ Heyd E Brothers KN Kudin VN

Staroverov R Kobayashi J Normand K Raghavachari A Rendell JC

Burant SS Iyengar J Tomasi M Cossi N Rega JM Millam M Klene JE

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Knox JB Cross V Bakken C Adamo J Jaramillo R Gomperts RE

Stratmann O Yazyev AJ Austin R Cammi C Pomelli JW Ochterski RL

Martin K Morokuma VG Zakrzewski GA Voth P Salvador JJ

Dannenberg S Dapprich AD Daniels O Farkas JB Foresman JV Ortiz J

Cioslowski DJ Fox GAUSSIAN 09 (Revision A01) Gaussian

IncWallingford CT (2009)

[21] A Brink HG Visser A Roodt Novel imino rhenium(I) tricarbonyl complexes

of salicylidene-derived ligands Synthesis X-ray crystallographic studies

spectroscopic characterization and DFT calculations Polyhedron 52 (2013) 416-

423

[22] J Mukiza TIA Gerber EC Hosten Decarboxylation of 5-amino-orotic acid

and a Schiff base derivative by rhenium(V) Inorg Chem Comm 57 (2015) 54-

57

[23] K Potgieter P Mayer T Gerber N Yumata E Hosten I Booysen R Betz M

Ismail B van Brecht Rhenium(I) tricarbonyl complexes with multidentate

nitrogen-donor derivatives Polyhedron 49 (2013) 67-73

[24] IN Booysen I Ebinumoliseh MP Akerman B Xulu A rhenium(I) compound

bearing a dimerized chromone NO bidentate chelator Inorg Chem Comm 62

(2015) 8-10

[25] P Mayer TIA Gerber B Buyambo A Abrahams Coordination behaviour of

acetylacetone-derived Schiff bases towards rhenium(I) and (V) Polyhedron 28

(2009) 1174-1178

[26] T Jurca O Ramadan I Korobkov DS Richeson Employing sterically

encumbered bis(imino)pyridine ligands in support of fac-rhenium(I) carbonyls

J Organomet Chem 802 (2016) 27-31

[27] J Ho WY Lee KJT Koh PPF Lee YK Yan Rhenium(I) tricarbonyl

complexes of salicylaldehyde semicarbazones Synthesis crystal structures and

cytotoxicity J Inorg Biochem 119 (2013) 10-20

[28] B Machura A Świtlicka M Wolff J Kusz R Kruszynski Mono- and di-

nuclear oxorhenium(V) complexes of 47-diphenyl-110-phenanthroline

Polyhedron 28 (2009) 3999-4009

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[29] B Machura M Jaworska P Lodowski Natural bond orbital analysis and

density functional study of linear and bent oxo-bridged dimers of rhenium(V)

J Mol Struc-Theochem 766 (2006) 1-8

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Highlights

bull Chromone rhenium(I) compounds

bull Simulated IR spectra

bull Low calculated RMSDs

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((imino)methylene)-12-ethane bridging moiety of 1 minimizes steric strain within its

chret chelator which effectively induces stability and prevents the transformation of

the chret ligand Furthermore compounds 1 and 2 exhibits good solubility in high

boiling point polar solvents including dimethylsulfoxide and dimethylformamide

while showing a relatively modest solubility in tetrahydrofuran and poor solubility

in chlorinated solvents such as chloroform The low molar conductivities [ΛM = 1693

and 2372 ohmcm2mol-1] of the metallic compounds indicates their neutrality in

DMSO

Broad vibrational bands are observed below 1700 cm-1 in the experimental IR

spectra of the metal complexes which could not be clearly assigned without the aid

of the simulated IR spectra of 1 and 2 see Figs S1 ndash S4 Both the experimental [2015

1871 cm-1 for 1 and 2] and simulated [2105 2018 2016 cm-1 for 1 and 2097 2017 1993

cm-1 for 2] IR spectra are dominated by the intense stretches of the carbonyl co-

ligands Similarly the ν(N-H) vibrations of 1 and 2 appear as weak intensity

vibrational bands in their respective simulated [3644 cm-1 for 1 and 3654 3289 cm-1

for 2] and experimental [2920 2850 cm-1 for 1 and 2915 cm-1 for 2] IR spectra The

simulated IR spectrum of 1 indicates distinctive vibrational bands associated with

the ketonic (at 1687 cm-1) imine (at 1567 cm-1) and ether (at 1469 cm-1) bonds

whereas the corresponding IR stretching frequencies can be found at 1655 cm-1 [for

ν(C=O)] 1464 cm-1 1615 [for ν(O-C-O)] and 1613 cm-1 [for ν(C=N)] in the

experimental IR spectrum of 1 Correlating the simulated IR spectrum of 2 with its

experimental IR spectrum revealed that the experimental vibrations for ν(C=O) are

found at 1628 and 1607 cm-1 while ν(C=N) and ν(O-C-O) appears at 1567 cm-1 and

1461 cm-1 respectively

In the proton NMR spectrum of 1 the aliphatic protons of the bridging ethane

moiety resonates as a multiplet between 469 and 439 ppm see Fig S6 A broad

singlet at 1091 ppm corresponds to the protons of the amino nitrogens of 1 but the

analogous protons were observed as two broad signals in the proton NMR spectrum

of the free-ligand chret see Fig S5 For 1 the aromatic protons of the chromone

moieties and the imino signal coalesce into two multiplets (viz 895 ndash 865 ppm and

812 ndash 711 ppm) in comparison to the corresponding well-resolved signals at 872

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ppm (for the imino protons) and 798 767 737 ppm (for the aromatic protons of the

chromone moieties) of the free-ligand chret The most intense signal in the 1H NMR

spectrum of 2 is due to the H1 proton positioned on the chromone moiety which

appears as a sharp singlet (at 969 ppm)

The benzimidazole proton in 2 resonates as an intense signal at 939 ppm

which integrates to one while the multiplet between 827 and 722 ppm are due to

the remaining aromatic peaks The presence of the pi-conjugated neutral chelators in

1 and 2 results in the occurrence of only intra-ligand - transitions in their UV-Vis

spectra see Figs S7 and S8 As expected no metal-based d-d transitions are

observed at more red-shifted regions due to the low-spin d6 electron configurations

of 1 and 2

32 Crystal structure of 1

Compound 1 co-crystallized with three tetrahydrofuran molecules of

recrystallization in its triclinic unit cell The crystal lattice of 1 is stabilized by a

network of classical intramolecular [Br1H4a-N4 = 273(4) Aring and Br2H2a-N2 =

260(4) Aring] and intermolecular hydrogen bonding [O11AH2b-N2 = 195(4) Aring and

O11BH4b-N4 = 191(5) Aring] see Fig S9 Collectively these hydrogen bonding

interactions allows molecules of 1 to pack in columns parallel to the [a]- and [b]-axes

The metal centres of 1 are positioned in the centre of the distorted

octahedrons which are largely imposed on by their constrained bite angles [O1-Re1-

N1 = 8452(7)ordm and N3-Re2-O6 = 8393(7)ordm] see Fig 2 Consequently the C2-Re1-Br1

[17685(8)ordm] O1-Re1-C3 [17741(9)ordm] C1-Re1-N1 [1762(1)ordm] Br2-Re2-C6 [17699(8)ordm]

C4-Re2-O6 [17641(9)ordm] and N3-Re2-C5 [1742(1)ordm] deviate all from linearity The

flexibility of the bridging ethane moiety affords narrower C=N-C [C18-N3-C19 =

1148(2)ordm and C16-N1-C17 = 1150(2)ordm] bond angles than the expected 120ordm for a bond

angle containing a central sp2 hybridized nitrogen Despite the influence of the

bridging ethane moiety the imino bonds [C16-N1 = 1286(4) Aring and C19-N3 =

1291(4) Aring] of 1 are in the range [1285(3) - 1312(6) Aring] observed for similar bonds

found in other Schiff bases [7 11 21 22 23] Across the respective octahedrons only

the Re1-C2 [1894(3) Aring] and Re2-C6 [1893(3) Aring] bonds are nearly equidistant which

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reflects similar trans-influence induced by the Br1 and Br2 atoms respectively

Hence the comparable cis-orientated organometallic bonds [Re1-C1 = 1942(3) Aring

Re1-C3 = 1897(3) Aring Re2-C4 = 1908(3) Aring and Re2-C5 = 1932(3) Aring] across the

octahedrons in 1 differs

The rhenium to ketonic [Re1-O1 = 2137(2) Aring and Re2-O6 = 2139(2) Aring] and

imino nitrogen [Re1-N1 = 2169(2) Aring and Re2-N3 = 2171(2) Aring] bonds are similar to

analogous bonds found within fac-[Re(CO)3(chrpychr)Br] (chrpychr = 2-(4-oxo-4H-

chromen-3-yl)-5H-chromeno[23-d]pyrimidin-5-one) and [(micro-O)ReOCl(amp)2]

(amp= 6-amino-3-methyl-1-phenyl-4-azahept-2-ene-1-one) [24 25] Bond orders with

the chret chelator is established based on the ketonic bonds [C14-O1 = 1259(4) Aring and

C28-O6 = 1261(3) Aring] being longer than the carbonyl bonds [eg C1-O3 = 1144(3) Aring]

but yet shorter than the ether bonds [eg C8-O2 = 1383(3) Aring and C21-O7 = 1347(4)

Aring] Also the localized C=C bonds in the chromone moeities remain intact after

coordination of the chret chelators as these C=C bonds [C7-C15 = 1414(4) Aring and

C20-C21 = 1411(4) Aring] are shorter than the C-C single bond [C17-C18 = 1537(3) Aring]

that constitutes the bridging ethane moeity

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Fig 2 An ORTEP view of compound 1 showing 50 probability displacement ellipsoids

and the atom labelling The tetrahydrofuran molecules of crystallization were omitted for

clarity

33 Crystal structure of 2

Four molecules of 2 occupies its monoclinic unit cell and each of these

molecules forms dimers with molecules of 2 in adjacent unit cells via classical

hydrogen-bonding interactions [Br1N2A-H2ABr1AN2-H = 257(3) Aring] see Fig

S10 Consequently molecules of 2 are self-assembled in columns aligned with the

[b]-axis Indicative to 1 the constrained bite angle [O1-Re-N1 = 8199(7)ordm] of 2 results

in the deviation of orthogonality in the opposing C17-Re-C19 [8690(1)ordm] bond angle

see Fig 3

The rhenium to halide bonds of 1 [Re1-Br1 = 26455(3) Aring and Re2-Br2 =

26377(3) Aring] and 2 [Re-Br = 26322(8) Aring] are comparable to those found in other facial

tricarbonyl rhenium complexes [26 27] All the remaining coordination bonds of 2

[Re-N1 = 2186(2) Aring Re-O1 = 2141(1) Aring Re-C17 = 1931(2) Aring Re-C18 = 1901(2) Aring

and Re-C19 = 1901(2) Aring] were similar to its chloro-analogue fac-[Re(CO)3(bzch)Cl]

viz Re-Oketone = 2137(2) Aring Re-Nbenzimidazole = 2179(2) Aring and Re-Ccarbonyl = 1929(2) Aring

1904(2) Aring 1898(2) Aring [11] Furthermore the double bond character of the C10-N1

bonds [1336(3) Aring] are clearly established when compared to the C-N bond lengths

[C10-N2 = 1358(3) Aring C16-N1 = 1401(3) Aring and C11-N2 = 1374(3) Aring] In addition the

bridging C9-C10 [1466(3) Aring] bond is single based on the more shorter localized C=C

[1365(3) Aring] chromone bond In turn the degrees of freedom around the C9-10 single

bond allows the chromone and benzimidazole plane to form a dihedral angle of

601ordm Also the benzimidazole and chromone moeities lies out of the plane of the

O1N1C19C17 mean basal plane by 1783ordm and 1837ordm respectively The toluene

molecule of recrystallization from an adjacent unit cell is nearly co-planar with the

bzch chelator of 1 indicating - interactions between this toluene molecule and the

bzch chelator (toluene Csp2 centroid to C9 = 3309 Aring and toluene Csp2 centroid to C10

= 3561 Aring)

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An evaluation of the experimental and optimized geometrical parameters for

the metal complexes reveals that the calculated intraligand bond distances [C17-C18

= 15374 Aring for 1 and C1-C9 = 13601 Aring for 2] and angles [O6-Re2-N3 = 83023ordm for 1

and O1-Re-N1 = 80800ordm for 2] compares well with their analogous experimental

geometrical parameters [C17-C18 = 1537(4) Aring for 1 C1-C9 = 1365(3) Aring for 2 O6-

Re2-N3 = 8393(7)ordm for 1 and O1-Re-N1 = 8199(7)ordm for 2] In addition the differences

in bond lengths found between comparable experimental [eg Re1-C1 = 1942(3) Aring

for 1 and Re-C19 = 1901(2) Aring] and optimized [eg Re1-C1 = 19344 Aring for 1 and Re-

C19 = 19034 Aring for 2] organometallic Re-CO bonds are not significant Discrepencies

found between the experimental [Re1-Br1 = 26455(3) Aring Re2-Br2 = 26377(3) Aring for 1

and Re-Br = 26322(8) Aring for 2] and calculated [Re1-Br1 = 272064 Aring Re2-Br2 = 272059

Aring for 1 and Re-Br = 266556 Aring for 2] rhenium to halide bonds are significant which

are ascribed to the rhenium atoms having lower calculated Natural Population

Analysis charges (0851 for Re12 in 1 and 0889 in 2) than the formal +I charge [28

29] The same trend is observed when examining the Re-Oketonic and Re-N

coordination bonds which were found to be longer in the computational models [eg

Re1-O1 = 21765 Aring Re1-N1 = 22224 Aring for 1 and Re-O1 = 22226 Aring Re-N1 = 23072 Aring

for 2] due to their lower Lewis acidic character of the metal centres than those in the

crystal structures [eg Re1-O1 = 2137(2) Aring Re1-N1 = 2169(2) Aring for 1 and Re-O1 =

2141(2) Aring Re-N1 = 2186(2) Aring for 2]

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Fig 3 An ORTEP view of complex 2 showing 50 probability displacement ellipsoids and

the atom labelling The toluene molecule of crystallization was omitted for clarity

Conclusion

Exploring the coordination behaviours of the diimine chret and chb afforded the di-

and mononuclear rhenium(I) compounds fac-(Re(CO)3Br)2(micro-chret) (1) and fac-

[Re(CO)3(bzch)Br] (2) The interpretation of the IR experimental spectra of the metal

compounds was supported by their simulated spectra calculated at the DFT level of

theory X-ray studies concured with the spectroscopic characterization revealing the

transformation of the chb diimine into the bzch chelator (in 2) and affirming the

coordination modes of the chb (in 1) and bzch (in 2) chelators In addition the 6-

membered chelate rings had a significant influence on the geometrical parameters of

the octahedral geometries of 1 and 2

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Supporting information

CCDC 1451521 and 1451522 contains crystallographic data for this article These data

can be obtained free of charge at wwwccdccamacukcontsretrievinghtml [or

from the Cambridge Crystallographic Data Centre (CCDC) 12 Union Road

Cambridge CB21EZ UK Fax +44(0)1223-336033 Email depositccdccamacuk]

Supplementary figures S1-S10 associated with this article can be found in the online

version

Acknowledgements

We are grateful to the University of KwaZulu-Natal and the National Research

Foundation of South Africa for financial support

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Table 1 Crystal data and structure refinement data

13(C4H8O) 2C7H8

Chemical formula C28H18Br2N4O10Re23(C4H8O) C19H10BrN2O5ReC7H8

Formula weight 131899 70453

TemperatureK 100(2) 100(2)

Crystal system Triclinic Monoclinic

Space group P-1 P21n

Unit cell dimensions (Ǻ deg) a = 128859(6) a = 12400(5)

b = 131199(6) b = 11778(5)

c = 149558(7) c = 16316(5)

α= 114601(2) α = 90000(5)

β = 98138(2) β = 92469(5)

γ = 102350(2) γ = 90000(5)

Crystal size (mm) 013 x 006 x 005 009 x 006 x 005

V(Aring3) 216873 (18) 238007(16)

Z 2 4

Density (calc) (mgm3) 2020 1966

Absorption coefficient (mm-1) 749 682

F(000) 1268 1352

θ range for data collection

(deg)

16 291 20 290

Reflections measured 41497 23824

Observed reflections [Igt2σ(I)] 10414 5621

Independent reflections 11421 6310

DataRestraintsparameters 114210566 56210321

Goodness of fit on F2 103 103

Observed R wR2 0018 0043 0020 0042

Rint 0018 0027

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Table 2 Selected bond lengths [Aring] and bond angles [deg] for 1 The RMSD of 1 is 0720 Aring

Experimental Optimized

Re1-Br1 26455(3) 272064 Re2-Br2 26377(3) 272059 Re1-O1 2137(2) 21765 Re2-O6 2139(2) 21764 Re1-N1 2169(2) 22224 Re2-N3 2171(2) 22224 Re1-C1 1942(3) 19344 Re1-C2 1894(3) 19091 Re1-C3 1897(3) 19071 Re2-C4 1908(3) 19071 Re2-C5 1932(3) 19091 Re2-C6 1893(2) 19343 C16-N1 1286(4) 12919 C19-N3 1291(4) 12919 C14-O1 1259(4) 12502 C28-O6 1261(3) 12503 C1-O3 1144(3) 11492 C8-O2 1383(3) 13796 C21-O7 1347(4) 13440 C7-C15 1414(4) 14102 C20-C21 1411(4) 14103 C17-C18 1537(3) 15374 O1-Re1-N1 8452(7) 83027 O6-Re2-N3 8393(7) 83023 C2-Re1-Br1 17685(8) 177228 O1-Re1-C3 17741(9) 176550 C1-Re1-N1 1762(1) 174310 Br2-Re2-C6 17699(8) 177236 C4-Re2-O6 17641(9) 176545 N3-Re2-C5 1742(1) 174309 C16-N1-C17 1150(2) 114920 C18-N3-C19 1148(2) 114920

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Table 3 Selected bond lengths [Aring] and bond angles [deg] for 2 The RMSD of 2 is 0267 Aring

Experimental Optimized

Re-Br 26322(8) 266556 Re-N1 2186(2) 23072 Re-O1 2141(2) 22226 Re-C17 1931(2) 19263 Re-C18 1901(2) 19150 Re-C19 1901(2) 19034 C9-C10 1466(3) 14608 C1-C9 1365(3) 13601 O1-Re-N1 8199(7) 80800 C17-Re-C19 8690(1) 88380 Br-Re-C18 17582(7) 176266

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[11] IN Booysen MB Ismail OQ Munro Mono- and dinuclear rhenium(I)

compounds with bidentate benzimidazole chelators Inorg Chem Commun 30

(2013) 168-172

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[12] IN Booysen MB Ismail MP Akerman Coordination behaviour of chromone

Schiff bases towards the [ReVO]3+ and [ReI(CO)3]+ cores J Coord Chem 66

(2013) 4371-4386

[13] S Bhatnagar S Sahir P Kackar S Kaushik MK Dave A Shukla A Goel

Synthesis and docking studies on styryl chromones exhibiting cytotoxicity in

human breast cancer cell line Bioorg Med Chem Lett 20 (2010) 4945-4950

[14] M Recanatini A Bisi A Cavalli F Belluti S Gobbi A Rampa P Valenti M

Palzer A Palusczak RW Hartmann A New Class of Nonsteroidal Aromatase

Inhibitorsthinsp Design and Synthesis of Chromone and Xanthone Derivatives and

Inhibition of the P450 Enzymes Aromatase and 17α-HydroxylaseC1720-

Lyase J Med Chem 44 (2001) 672-680

[15] IN Booysen A Adebisi MP Akerman OQ Munro B Xulu Coordination of

di- and triimine ligands at ruthenium(II) and ruthenium(III) centers structural

electrochemical and radical scavenging studies J Coord Chem (2016) doi

1010800095897220161177177

[16] Bruker APEX2 SAINT and SADABS Bruker AXS Inc (2010) Madison

Wisconsin USA

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A51 (1995) 33-38

[18] GM Sheldrick A short history of SHELX Acta Cryst A64 (2008) 112-122

[19] LJ Farrugia WinGX and ORTEP for Windows an update J Appl Cryst 45

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[20] MJ Frisch GW Trucks HB Schlegel GE Scuseria MA Robb JR

Cheeseman G Scalmani V Barone B Mennucci GA Petersson H Nakatsuji

M Caricato X Li HP Hratchian AF Izmaylov J Bloino G Zheng JL

Sonnenberg M Hada M Ehara K Toyota R Fukuda J Hasegawa M Ishida

T Nakajima Y Honda O Kitao H Nakai T Vreven JA Montgomery Jr JE

Peralta F Ogliaro M Bearpark JJ Heyd E Brothers KN Kudin VN

Staroverov R Kobayashi J Normand K Raghavachari A Rendell JC

Burant SS Iyengar J Tomasi M Cossi N Rega JM Millam M Klene JE

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Knox JB Cross V Bakken C Adamo J Jaramillo R Gomperts RE

Stratmann O Yazyev AJ Austin R Cammi C Pomelli JW Ochterski RL

Martin K Morokuma VG Zakrzewski GA Voth P Salvador JJ

Dannenberg S Dapprich AD Daniels O Farkas JB Foresman JV Ortiz J

Cioslowski DJ Fox GAUSSIAN 09 (Revision A01) Gaussian

IncWallingford CT (2009)

[21] A Brink HG Visser A Roodt Novel imino rhenium(I) tricarbonyl complexes

of salicylidene-derived ligands Synthesis X-ray crystallographic studies

spectroscopic characterization and DFT calculations Polyhedron 52 (2013) 416-

423

[22] J Mukiza TIA Gerber EC Hosten Decarboxylation of 5-amino-orotic acid

and a Schiff base derivative by rhenium(V) Inorg Chem Comm 57 (2015) 54-

57

[23] K Potgieter P Mayer T Gerber N Yumata E Hosten I Booysen R Betz M

Ismail B van Brecht Rhenium(I) tricarbonyl complexes with multidentate

nitrogen-donor derivatives Polyhedron 49 (2013) 67-73

[24] IN Booysen I Ebinumoliseh MP Akerman B Xulu A rhenium(I) compound

bearing a dimerized chromone NO bidentate chelator Inorg Chem Comm 62

(2015) 8-10

[25] P Mayer TIA Gerber B Buyambo A Abrahams Coordination behaviour of

acetylacetone-derived Schiff bases towards rhenium(I) and (V) Polyhedron 28

(2009) 1174-1178

[26] T Jurca O Ramadan I Korobkov DS Richeson Employing sterically

encumbered bis(imino)pyridine ligands in support of fac-rhenium(I) carbonyls

J Organomet Chem 802 (2016) 27-31

[27] J Ho WY Lee KJT Koh PPF Lee YK Yan Rhenium(I) tricarbonyl

complexes of salicylaldehyde semicarbazones Synthesis crystal structures and

cytotoxicity J Inorg Biochem 119 (2013) 10-20

[28] B Machura A Świtlicka M Wolff J Kusz R Kruszynski Mono- and di-

nuclear oxorhenium(V) complexes of 47-diphenyl-110-phenanthroline

Polyhedron 28 (2009) 3999-4009

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[29] B Machura M Jaworska P Lodowski Natural bond orbital analysis and

density functional study of linear and bent oxo-bridged dimers of rhenium(V)

J Mol Struc-Theochem 766 (2006) 1-8

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Highlights

bull Chromone rhenium(I) compounds

bull Simulated IR spectra

bull Low calculated RMSDs

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ppm (for the imino protons) and 798 767 737 ppm (for the aromatic protons of the

chromone moieties) of the free-ligand chret The most intense signal in the 1H NMR

spectrum of 2 is due to the H1 proton positioned on the chromone moiety which

appears as a sharp singlet (at 969 ppm)

The benzimidazole proton in 2 resonates as an intense signal at 939 ppm

which integrates to one while the multiplet between 827 and 722 ppm are due to

the remaining aromatic peaks The presence of the pi-conjugated neutral chelators in

1 and 2 results in the occurrence of only intra-ligand - transitions in their UV-Vis

spectra see Figs S7 and S8 As expected no metal-based d-d transitions are

observed at more red-shifted regions due to the low-spin d6 electron configurations

of 1 and 2

32 Crystal structure of 1

Compound 1 co-crystallized with three tetrahydrofuran molecules of

recrystallization in its triclinic unit cell The crystal lattice of 1 is stabilized by a

network of classical intramolecular [Br1H4a-N4 = 273(4) Aring and Br2H2a-N2 =

260(4) Aring] and intermolecular hydrogen bonding [O11AH2b-N2 = 195(4) Aring and

O11BH4b-N4 = 191(5) Aring] see Fig S9 Collectively these hydrogen bonding

interactions allows molecules of 1 to pack in columns parallel to the [a]- and [b]-axes

The metal centres of 1 are positioned in the centre of the distorted

octahedrons which are largely imposed on by their constrained bite angles [O1-Re1-

N1 = 8452(7)ordm and N3-Re2-O6 = 8393(7)ordm] see Fig 2 Consequently the C2-Re1-Br1

[17685(8)ordm] O1-Re1-C3 [17741(9)ordm] C1-Re1-N1 [1762(1)ordm] Br2-Re2-C6 [17699(8)ordm]

C4-Re2-O6 [17641(9)ordm] and N3-Re2-C5 [1742(1)ordm] deviate all from linearity The

flexibility of the bridging ethane moiety affords narrower C=N-C [C18-N3-C19 =

1148(2)ordm and C16-N1-C17 = 1150(2)ordm] bond angles than the expected 120ordm for a bond

angle containing a central sp2 hybridized nitrogen Despite the influence of the

bridging ethane moiety the imino bonds [C16-N1 = 1286(4) Aring and C19-N3 =

1291(4) Aring] of 1 are in the range [1285(3) - 1312(6) Aring] observed for similar bonds

found in other Schiff bases [7 11 21 22 23] Across the respective octahedrons only

the Re1-C2 [1894(3) Aring] and Re2-C6 [1893(3) Aring] bonds are nearly equidistant which

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reflects similar trans-influence induced by the Br1 and Br2 atoms respectively

Hence the comparable cis-orientated organometallic bonds [Re1-C1 = 1942(3) Aring

Re1-C3 = 1897(3) Aring Re2-C4 = 1908(3) Aring and Re2-C5 = 1932(3) Aring] across the

octahedrons in 1 differs

The rhenium to ketonic [Re1-O1 = 2137(2) Aring and Re2-O6 = 2139(2) Aring] and

imino nitrogen [Re1-N1 = 2169(2) Aring and Re2-N3 = 2171(2) Aring] bonds are similar to

analogous bonds found within fac-[Re(CO)3(chrpychr)Br] (chrpychr = 2-(4-oxo-4H-

chromen-3-yl)-5H-chromeno[23-d]pyrimidin-5-one) and [(micro-O)ReOCl(amp)2]

(amp= 6-amino-3-methyl-1-phenyl-4-azahept-2-ene-1-one) [24 25] Bond orders with

the chret chelator is established based on the ketonic bonds [C14-O1 = 1259(4) Aring and

C28-O6 = 1261(3) Aring] being longer than the carbonyl bonds [eg C1-O3 = 1144(3) Aring]

but yet shorter than the ether bonds [eg C8-O2 = 1383(3) Aring and C21-O7 = 1347(4)

Aring] Also the localized C=C bonds in the chromone moeities remain intact after

coordination of the chret chelators as these C=C bonds [C7-C15 = 1414(4) Aring and

C20-C21 = 1411(4) Aring] are shorter than the C-C single bond [C17-C18 = 1537(3) Aring]

that constitutes the bridging ethane moeity

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Fig 2 An ORTEP view of compound 1 showing 50 probability displacement ellipsoids

and the atom labelling The tetrahydrofuran molecules of crystallization were omitted for

clarity

33 Crystal structure of 2

Four molecules of 2 occupies its monoclinic unit cell and each of these

molecules forms dimers with molecules of 2 in adjacent unit cells via classical

hydrogen-bonding interactions [Br1N2A-H2ABr1AN2-H = 257(3) Aring] see Fig

S10 Consequently molecules of 2 are self-assembled in columns aligned with the

[b]-axis Indicative to 1 the constrained bite angle [O1-Re-N1 = 8199(7)ordm] of 2 results

in the deviation of orthogonality in the opposing C17-Re-C19 [8690(1)ordm] bond angle

see Fig 3

The rhenium to halide bonds of 1 [Re1-Br1 = 26455(3) Aring and Re2-Br2 =

26377(3) Aring] and 2 [Re-Br = 26322(8) Aring] are comparable to those found in other facial

tricarbonyl rhenium complexes [26 27] All the remaining coordination bonds of 2

[Re-N1 = 2186(2) Aring Re-O1 = 2141(1) Aring Re-C17 = 1931(2) Aring Re-C18 = 1901(2) Aring

and Re-C19 = 1901(2) Aring] were similar to its chloro-analogue fac-[Re(CO)3(bzch)Cl]

viz Re-Oketone = 2137(2) Aring Re-Nbenzimidazole = 2179(2) Aring and Re-Ccarbonyl = 1929(2) Aring

1904(2) Aring 1898(2) Aring [11] Furthermore the double bond character of the C10-N1

bonds [1336(3) Aring] are clearly established when compared to the C-N bond lengths

[C10-N2 = 1358(3) Aring C16-N1 = 1401(3) Aring and C11-N2 = 1374(3) Aring] In addition the

bridging C9-C10 [1466(3) Aring] bond is single based on the more shorter localized C=C

[1365(3) Aring] chromone bond In turn the degrees of freedom around the C9-10 single

bond allows the chromone and benzimidazole plane to form a dihedral angle of

601ordm Also the benzimidazole and chromone moeities lies out of the plane of the

O1N1C19C17 mean basal plane by 1783ordm and 1837ordm respectively The toluene

molecule of recrystallization from an adjacent unit cell is nearly co-planar with the

bzch chelator of 1 indicating - interactions between this toluene molecule and the

bzch chelator (toluene Csp2 centroid to C9 = 3309 Aring and toluene Csp2 centroid to C10

= 3561 Aring)

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An evaluation of the experimental and optimized geometrical parameters for

the metal complexes reveals that the calculated intraligand bond distances [C17-C18

= 15374 Aring for 1 and C1-C9 = 13601 Aring for 2] and angles [O6-Re2-N3 = 83023ordm for 1

and O1-Re-N1 = 80800ordm for 2] compares well with their analogous experimental

geometrical parameters [C17-C18 = 1537(4) Aring for 1 C1-C9 = 1365(3) Aring for 2 O6-

Re2-N3 = 8393(7)ordm for 1 and O1-Re-N1 = 8199(7)ordm for 2] In addition the differences

in bond lengths found between comparable experimental [eg Re1-C1 = 1942(3) Aring

for 1 and Re-C19 = 1901(2) Aring] and optimized [eg Re1-C1 = 19344 Aring for 1 and Re-

C19 = 19034 Aring for 2] organometallic Re-CO bonds are not significant Discrepencies

found between the experimental [Re1-Br1 = 26455(3) Aring Re2-Br2 = 26377(3) Aring for 1

and Re-Br = 26322(8) Aring for 2] and calculated [Re1-Br1 = 272064 Aring Re2-Br2 = 272059

Aring for 1 and Re-Br = 266556 Aring for 2] rhenium to halide bonds are significant which

are ascribed to the rhenium atoms having lower calculated Natural Population

Analysis charges (0851 for Re12 in 1 and 0889 in 2) than the formal +I charge [28

29] The same trend is observed when examining the Re-Oketonic and Re-N

coordination bonds which were found to be longer in the computational models [eg

Re1-O1 = 21765 Aring Re1-N1 = 22224 Aring for 1 and Re-O1 = 22226 Aring Re-N1 = 23072 Aring

for 2] due to their lower Lewis acidic character of the metal centres than those in the

crystal structures [eg Re1-O1 = 2137(2) Aring Re1-N1 = 2169(2) Aring for 1 and Re-O1 =

2141(2) Aring Re-N1 = 2186(2) Aring for 2]

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Fig 3 An ORTEP view of complex 2 showing 50 probability displacement ellipsoids and

the atom labelling The toluene molecule of crystallization was omitted for clarity

Conclusion

Exploring the coordination behaviours of the diimine chret and chb afforded the di-

and mononuclear rhenium(I) compounds fac-(Re(CO)3Br)2(micro-chret) (1) and fac-

[Re(CO)3(bzch)Br] (2) The interpretation of the IR experimental spectra of the metal

compounds was supported by their simulated spectra calculated at the DFT level of

theory X-ray studies concured with the spectroscopic characterization revealing the

transformation of the chb diimine into the bzch chelator (in 2) and affirming the

coordination modes of the chb (in 1) and bzch (in 2) chelators In addition the 6-

membered chelate rings had a significant influence on the geometrical parameters of

the octahedral geometries of 1 and 2

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Supporting information

CCDC 1451521 and 1451522 contains crystallographic data for this article These data

can be obtained free of charge at wwwccdccamacukcontsretrievinghtml [or

from the Cambridge Crystallographic Data Centre (CCDC) 12 Union Road

Cambridge CB21EZ UK Fax +44(0)1223-336033 Email depositccdccamacuk]

Supplementary figures S1-S10 associated with this article can be found in the online

version

Acknowledgements

We are grateful to the University of KwaZulu-Natal and the National Research

Foundation of South Africa for financial support

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Table 1 Crystal data and structure refinement data

13(C4H8O) 2C7H8

Chemical formula C28H18Br2N4O10Re23(C4H8O) C19H10BrN2O5ReC7H8

Formula weight 131899 70453

TemperatureK 100(2) 100(2)

Crystal system Triclinic Monoclinic

Space group P-1 P21n

Unit cell dimensions (Ǻ deg) a = 128859(6) a = 12400(5)

b = 131199(6) b = 11778(5)

c = 149558(7) c = 16316(5)

α= 114601(2) α = 90000(5)

β = 98138(2) β = 92469(5)

γ = 102350(2) γ = 90000(5)

Crystal size (mm) 013 x 006 x 005 009 x 006 x 005

V(Aring3) 216873 (18) 238007(16)

Z 2 4

Density (calc) (mgm3) 2020 1966

Absorption coefficient (mm-1) 749 682

F(000) 1268 1352

θ range for data collection

(deg)

16 291 20 290

Reflections measured 41497 23824

Observed reflections [Igt2σ(I)] 10414 5621

Independent reflections 11421 6310

DataRestraintsparameters 114210566 56210321

Goodness of fit on F2 103 103

Observed R wR2 0018 0043 0020 0042

Rint 0018 0027

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Table 2 Selected bond lengths [Aring] and bond angles [deg] for 1 The RMSD of 1 is 0720 Aring

Experimental Optimized

Re1-Br1 26455(3) 272064 Re2-Br2 26377(3) 272059 Re1-O1 2137(2) 21765 Re2-O6 2139(2) 21764 Re1-N1 2169(2) 22224 Re2-N3 2171(2) 22224 Re1-C1 1942(3) 19344 Re1-C2 1894(3) 19091 Re1-C3 1897(3) 19071 Re2-C4 1908(3) 19071 Re2-C5 1932(3) 19091 Re2-C6 1893(2) 19343 C16-N1 1286(4) 12919 C19-N3 1291(4) 12919 C14-O1 1259(4) 12502 C28-O6 1261(3) 12503 C1-O3 1144(3) 11492 C8-O2 1383(3) 13796 C21-O7 1347(4) 13440 C7-C15 1414(4) 14102 C20-C21 1411(4) 14103 C17-C18 1537(3) 15374 O1-Re1-N1 8452(7) 83027 O6-Re2-N3 8393(7) 83023 C2-Re1-Br1 17685(8) 177228 O1-Re1-C3 17741(9) 176550 C1-Re1-N1 1762(1) 174310 Br2-Re2-C6 17699(8) 177236 C4-Re2-O6 17641(9) 176545 N3-Re2-C5 1742(1) 174309 C16-N1-C17 1150(2) 114920 C18-N3-C19 1148(2) 114920

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Table 3 Selected bond lengths [Aring] and bond angles [deg] for 2 The RMSD of 2 is 0267 Aring

Experimental Optimized

Re-Br 26322(8) 266556 Re-N1 2186(2) 23072 Re-O1 2141(2) 22226 Re-C17 1931(2) 19263 Re-C18 1901(2) 19150 Re-C19 1901(2) 19034 C9-C10 1466(3) 14608 C1-C9 1365(3) 13601 O1-Re-N1 8199(7) 80800 C17-Re-C19 8690(1) 88380 Br-Re-C18 17582(7) 176266

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[12] IN Booysen MB Ismail MP Akerman Coordination behaviour of chromone

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[13] S Bhatnagar S Sahir P Kackar S Kaushik MK Dave A Shukla A Goel

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[14] M Recanatini A Bisi A Cavalli F Belluti S Gobbi A Rampa P Valenti M

Palzer A Palusczak RW Hartmann A New Class of Nonsteroidal Aromatase

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[15] IN Booysen A Adebisi MP Akerman OQ Munro B Xulu Coordination of

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[20] MJ Frisch GW Trucks HB Schlegel GE Scuseria MA Robb JR

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Sonnenberg M Hada M Ehara K Toyota R Fukuda J Hasegawa M Ishida

T Nakajima Y Honda O Kitao H Nakai T Vreven JA Montgomery Jr JE

Peralta F Ogliaro M Bearpark JJ Heyd E Brothers KN Kudin VN

Staroverov R Kobayashi J Normand K Raghavachari A Rendell JC

Burant SS Iyengar J Tomasi M Cossi N Rega JM Millam M Klene JE

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Knox JB Cross V Bakken C Adamo J Jaramillo R Gomperts RE

Stratmann O Yazyev AJ Austin R Cammi C Pomelli JW Ochterski RL

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[21] A Brink HG Visser A Roodt Novel imino rhenium(I) tricarbonyl complexes

of salicylidene-derived ligands Synthesis X-ray crystallographic studies

spectroscopic characterization and DFT calculations Polyhedron 52 (2013) 416-

423

[22] J Mukiza TIA Gerber EC Hosten Decarboxylation of 5-amino-orotic acid

and a Schiff base derivative by rhenium(V) Inorg Chem Comm 57 (2015) 54-

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[23] K Potgieter P Mayer T Gerber N Yumata E Hosten I Booysen R Betz M

Ismail B van Brecht Rhenium(I) tricarbonyl complexes with multidentate

nitrogen-donor derivatives Polyhedron 49 (2013) 67-73

[24] IN Booysen I Ebinumoliseh MP Akerman B Xulu A rhenium(I) compound

bearing a dimerized chromone NO bidentate chelator Inorg Chem Comm 62

(2015) 8-10

[25] P Mayer TIA Gerber B Buyambo A Abrahams Coordination behaviour of

acetylacetone-derived Schiff bases towards rhenium(I) and (V) Polyhedron 28

(2009) 1174-1178

[26] T Jurca O Ramadan I Korobkov DS Richeson Employing sterically

encumbered bis(imino)pyridine ligands in support of fac-rhenium(I) carbonyls

J Organomet Chem 802 (2016) 27-31

[27] J Ho WY Lee KJT Koh PPF Lee YK Yan Rhenium(I) tricarbonyl

complexes of salicylaldehyde semicarbazones Synthesis crystal structures and

cytotoxicity J Inorg Biochem 119 (2013) 10-20

[28] B Machura A Świtlicka M Wolff J Kusz R Kruszynski Mono- and di-

nuclear oxorhenium(V) complexes of 47-diphenyl-110-phenanthroline

Polyhedron 28 (2009) 3999-4009

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[29] B Machura M Jaworska P Lodowski Natural bond orbital analysis and

density functional study of linear and bent oxo-bridged dimers of rhenium(V)

J Mol Struc-Theochem 766 (2006) 1-8

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Highlights

bull Chromone rhenium(I) compounds

bull Simulated IR spectra

bull Low calculated RMSDs

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reflects similar trans-influence induced by the Br1 and Br2 atoms respectively

Hence the comparable cis-orientated organometallic bonds [Re1-C1 = 1942(3) Aring

Re1-C3 = 1897(3) Aring Re2-C4 = 1908(3) Aring and Re2-C5 = 1932(3) Aring] across the

octahedrons in 1 differs

The rhenium to ketonic [Re1-O1 = 2137(2) Aring and Re2-O6 = 2139(2) Aring] and

imino nitrogen [Re1-N1 = 2169(2) Aring and Re2-N3 = 2171(2) Aring] bonds are similar to

analogous bonds found within fac-[Re(CO)3(chrpychr)Br] (chrpychr = 2-(4-oxo-4H-

chromen-3-yl)-5H-chromeno[23-d]pyrimidin-5-one) and [(micro-O)ReOCl(amp)2]

(amp= 6-amino-3-methyl-1-phenyl-4-azahept-2-ene-1-one) [24 25] Bond orders with

the chret chelator is established based on the ketonic bonds [C14-O1 = 1259(4) Aring and

C28-O6 = 1261(3) Aring] being longer than the carbonyl bonds [eg C1-O3 = 1144(3) Aring]

but yet shorter than the ether bonds [eg C8-O2 = 1383(3) Aring and C21-O7 = 1347(4)

Aring] Also the localized C=C bonds in the chromone moeities remain intact after

coordination of the chret chelators as these C=C bonds [C7-C15 = 1414(4) Aring and

C20-C21 = 1411(4) Aring] are shorter than the C-C single bond [C17-C18 = 1537(3) Aring]

that constitutes the bridging ethane moeity

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Fig 2 An ORTEP view of compound 1 showing 50 probability displacement ellipsoids

and the atom labelling The tetrahydrofuran molecules of crystallization were omitted for

clarity

33 Crystal structure of 2

Four molecules of 2 occupies its monoclinic unit cell and each of these

molecules forms dimers with molecules of 2 in adjacent unit cells via classical

hydrogen-bonding interactions [Br1N2A-H2ABr1AN2-H = 257(3) Aring] see Fig

S10 Consequently molecules of 2 are self-assembled in columns aligned with the

[b]-axis Indicative to 1 the constrained bite angle [O1-Re-N1 = 8199(7)ordm] of 2 results

in the deviation of orthogonality in the opposing C17-Re-C19 [8690(1)ordm] bond angle

see Fig 3

The rhenium to halide bonds of 1 [Re1-Br1 = 26455(3) Aring and Re2-Br2 =

26377(3) Aring] and 2 [Re-Br = 26322(8) Aring] are comparable to those found in other facial

tricarbonyl rhenium complexes [26 27] All the remaining coordination bonds of 2

[Re-N1 = 2186(2) Aring Re-O1 = 2141(1) Aring Re-C17 = 1931(2) Aring Re-C18 = 1901(2) Aring

and Re-C19 = 1901(2) Aring] were similar to its chloro-analogue fac-[Re(CO)3(bzch)Cl]

viz Re-Oketone = 2137(2) Aring Re-Nbenzimidazole = 2179(2) Aring and Re-Ccarbonyl = 1929(2) Aring

1904(2) Aring 1898(2) Aring [11] Furthermore the double bond character of the C10-N1

bonds [1336(3) Aring] are clearly established when compared to the C-N bond lengths

[C10-N2 = 1358(3) Aring C16-N1 = 1401(3) Aring and C11-N2 = 1374(3) Aring] In addition the

bridging C9-C10 [1466(3) Aring] bond is single based on the more shorter localized C=C

[1365(3) Aring] chromone bond In turn the degrees of freedom around the C9-10 single

bond allows the chromone and benzimidazole plane to form a dihedral angle of

601ordm Also the benzimidazole and chromone moeities lies out of the plane of the

O1N1C19C17 mean basal plane by 1783ordm and 1837ordm respectively The toluene

molecule of recrystallization from an adjacent unit cell is nearly co-planar with the

bzch chelator of 1 indicating - interactions between this toluene molecule and the

bzch chelator (toluene Csp2 centroid to C9 = 3309 Aring and toluene Csp2 centroid to C10

= 3561 Aring)

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An evaluation of the experimental and optimized geometrical parameters for

the metal complexes reveals that the calculated intraligand bond distances [C17-C18

= 15374 Aring for 1 and C1-C9 = 13601 Aring for 2] and angles [O6-Re2-N3 = 83023ordm for 1

and O1-Re-N1 = 80800ordm for 2] compares well with their analogous experimental

geometrical parameters [C17-C18 = 1537(4) Aring for 1 C1-C9 = 1365(3) Aring for 2 O6-

Re2-N3 = 8393(7)ordm for 1 and O1-Re-N1 = 8199(7)ordm for 2] In addition the differences

in bond lengths found between comparable experimental [eg Re1-C1 = 1942(3) Aring

for 1 and Re-C19 = 1901(2) Aring] and optimized [eg Re1-C1 = 19344 Aring for 1 and Re-

C19 = 19034 Aring for 2] organometallic Re-CO bonds are not significant Discrepencies

found between the experimental [Re1-Br1 = 26455(3) Aring Re2-Br2 = 26377(3) Aring for 1

and Re-Br = 26322(8) Aring for 2] and calculated [Re1-Br1 = 272064 Aring Re2-Br2 = 272059

Aring for 1 and Re-Br = 266556 Aring for 2] rhenium to halide bonds are significant which

are ascribed to the rhenium atoms having lower calculated Natural Population

Analysis charges (0851 for Re12 in 1 and 0889 in 2) than the formal +I charge [28

29] The same trend is observed when examining the Re-Oketonic and Re-N

coordination bonds which were found to be longer in the computational models [eg

Re1-O1 = 21765 Aring Re1-N1 = 22224 Aring for 1 and Re-O1 = 22226 Aring Re-N1 = 23072 Aring

for 2] due to their lower Lewis acidic character of the metal centres than those in the

crystal structures [eg Re1-O1 = 2137(2) Aring Re1-N1 = 2169(2) Aring for 1 and Re-O1 =

2141(2) Aring Re-N1 = 2186(2) Aring for 2]

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Fig 3 An ORTEP view of complex 2 showing 50 probability displacement ellipsoids and

the atom labelling The toluene molecule of crystallization was omitted for clarity

Conclusion

Exploring the coordination behaviours of the diimine chret and chb afforded the di-

and mononuclear rhenium(I) compounds fac-(Re(CO)3Br)2(micro-chret) (1) and fac-

[Re(CO)3(bzch)Br] (2) The interpretation of the IR experimental spectra of the metal

compounds was supported by their simulated spectra calculated at the DFT level of

theory X-ray studies concured with the spectroscopic characterization revealing the

transformation of the chb diimine into the bzch chelator (in 2) and affirming the

coordination modes of the chb (in 1) and bzch (in 2) chelators In addition the 6-

membered chelate rings had a significant influence on the geometrical parameters of

the octahedral geometries of 1 and 2

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Supporting information

CCDC 1451521 and 1451522 contains crystallographic data for this article These data

can be obtained free of charge at wwwccdccamacukcontsretrievinghtml [or

from the Cambridge Crystallographic Data Centre (CCDC) 12 Union Road

Cambridge CB21EZ UK Fax +44(0)1223-336033 Email depositccdccamacuk]

Supplementary figures S1-S10 associated with this article can be found in the online

version

Acknowledgements

We are grateful to the University of KwaZulu-Natal and the National Research

Foundation of South Africa for financial support

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Table 1 Crystal data and structure refinement data

13(C4H8O) 2C7H8

Chemical formula C28H18Br2N4O10Re23(C4H8O) C19H10BrN2O5ReC7H8

Formula weight 131899 70453

TemperatureK 100(2) 100(2)

Crystal system Triclinic Monoclinic

Space group P-1 P21n

Unit cell dimensions (Ǻ deg) a = 128859(6) a = 12400(5)

b = 131199(6) b = 11778(5)

c = 149558(7) c = 16316(5)

α= 114601(2) α = 90000(5)

β = 98138(2) β = 92469(5)

γ = 102350(2) γ = 90000(5)

Crystal size (mm) 013 x 006 x 005 009 x 006 x 005

V(Aring3) 216873 (18) 238007(16)

Z 2 4

Density (calc) (mgm3) 2020 1966

Absorption coefficient (mm-1) 749 682

F(000) 1268 1352

θ range for data collection

(deg)

16 291 20 290

Reflections measured 41497 23824

Observed reflections [Igt2σ(I)] 10414 5621

Independent reflections 11421 6310

DataRestraintsparameters 114210566 56210321

Goodness of fit on F2 103 103

Observed R wR2 0018 0043 0020 0042

Rint 0018 0027

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Table 2 Selected bond lengths [Aring] and bond angles [deg] for 1 The RMSD of 1 is 0720 Aring

Experimental Optimized

Re1-Br1 26455(3) 272064 Re2-Br2 26377(3) 272059 Re1-O1 2137(2) 21765 Re2-O6 2139(2) 21764 Re1-N1 2169(2) 22224 Re2-N3 2171(2) 22224 Re1-C1 1942(3) 19344 Re1-C2 1894(3) 19091 Re1-C3 1897(3) 19071 Re2-C4 1908(3) 19071 Re2-C5 1932(3) 19091 Re2-C6 1893(2) 19343 C16-N1 1286(4) 12919 C19-N3 1291(4) 12919 C14-O1 1259(4) 12502 C28-O6 1261(3) 12503 C1-O3 1144(3) 11492 C8-O2 1383(3) 13796 C21-O7 1347(4) 13440 C7-C15 1414(4) 14102 C20-C21 1411(4) 14103 C17-C18 1537(3) 15374 O1-Re1-N1 8452(7) 83027 O6-Re2-N3 8393(7) 83023 C2-Re1-Br1 17685(8) 177228 O1-Re1-C3 17741(9) 176550 C1-Re1-N1 1762(1) 174310 Br2-Re2-C6 17699(8) 177236 C4-Re2-O6 17641(9) 176545 N3-Re2-C5 1742(1) 174309 C16-N1-C17 1150(2) 114920 C18-N3-C19 1148(2) 114920

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Table 3 Selected bond lengths [Aring] and bond angles [deg] for 2 The RMSD of 2 is 0267 Aring

Experimental Optimized

Re-Br 26322(8) 266556 Re-N1 2186(2) 23072 Re-O1 2141(2) 22226 Re-C17 1931(2) 19263 Re-C18 1901(2) 19150 Re-C19 1901(2) 19034 C9-C10 1466(3) 14608 C1-C9 1365(3) 13601 O1-Re-N1 8199(7) 80800 C17-Re-C19 8690(1) 88380 Br-Re-C18 17582(7) 176266

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References

[1] JR Dilworth SJ Parrott The biomedical chemistry of technetium and

rhenium Chem Soc Rev 27 (1998) 43-55

[2] S Jurisson D Berning J Wei M Dangshe Coordination compounds in

nuclear medicine Chem Rev 93 (1993) 1137-1156

[3] S Juumlrgens WA Herrmann FE Kuumlhn Rhenium and technetium based

radiopharmaceuticals Development and recent advances J Organomet Chem

751 (2014) 83-89

[4] U Abram R Alberto Technetium and Rhenium - Coordination Chemistry and

Nuclear Medical Applications Braz Chem Soc 17 (2006) 1486-1500

[5] SL Binkley TC Leeper RS Rowlett RS Herrick CJ Ziegler

Re(CO)3(H2O)3+ binding to lysozyme structure and reactivity Mettalomics 3

(2011) 909-916

[6] RS Herrick TJ Brunker C Maus K Crandall A Cetin CJ

Ziegler Aqueous preparation and physiological stability studies of

Re(CO)3(tripodal) compounds Chem Commun (2006) 4330-4331

[7] K Potgieter P Mayer TIA Gerber IN Booysen Coordination behaviour of

the multidentate Schiff base 26-bis(2-hydroxyphenyliminomethyl)pyridine

towards the fac-[Re(CO)3]+ and [ReO]3+ cores Polyhedron 28 (2009) 2808-2812

[8] CL Ferreira CB Ewart SR Bayly B O Patrick J Steele MJ Adam C

Orvig Glucosamine Conjugates of Tricarbonylcyclopentadienyl Rhenium(I)

and Technetium(I) Cores Inorg Chem 45 (2006) 6979-6987

[9] Q Nadeem D Can Y Shen M Felber Z Mahmooda R Alberto Synthesis of

tripeptide derivatized cyclopentadienyl complexes of technetium and rhenium

as radiopharmaceutical probes Org Biomol Chem 12 (2014) 1966-1974

[10] IN Booysen M Ismail TIA Gerber M Akerman B Van Brecht Oxo and

oxofree rhenium(V) complexes with NO-donor Schiff bases S Afr J Chem 65

(2012) 174-177

[11] IN Booysen MB Ismail OQ Munro Mono- and dinuclear rhenium(I)

compounds with bidentate benzimidazole chelators Inorg Chem Commun 30

(2013) 168-172

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[12] IN Booysen MB Ismail MP Akerman Coordination behaviour of chromone

Schiff bases towards the [ReVO]3+ and [ReI(CO)3]+ cores J Coord Chem 66

(2013) 4371-4386

[13] S Bhatnagar S Sahir P Kackar S Kaushik MK Dave A Shukla A Goel

Synthesis and docking studies on styryl chromones exhibiting cytotoxicity in

human breast cancer cell line Bioorg Med Chem Lett 20 (2010) 4945-4950

[14] M Recanatini A Bisi A Cavalli F Belluti S Gobbi A Rampa P Valenti M

Palzer A Palusczak RW Hartmann A New Class of Nonsteroidal Aromatase

Inhibitorsthinsp Design and Synthesis of Chromone and Xanthone Derivatives and

Inhibition of the P450 Enzymes Aromatase and 17α-HydroxylaseC1720-

Lyase J Med Chem 44 (2001) 672-680

[15] IN Booysen A Adebisi MP Akerman OQ Munro B Xulu Coordination of

di- and triimine ligands at ruthenium(II) and ruthenium(III) centers structural

electrochemical and radical scavenging studies J Coord Chem (2016) doi

1010800095897220161177177

[16] Bruker APEX2 SAINT and SADABS Bruker AXS Inc (2010) Madison

Wisconsin USA

[17] RH Blessing An empirical correction for absorption anisotropy Acta Cryst

A51 (1995) 33-38

[18] GM Sheldrick A short history of SHELX Acta Cryst A64 (2008) 112-122

[19] LJ Farrugia WinGX and ORTEP for Windows an update J Appl Cryst 45

(2012) 849-854

[20] MJ Frisch GW Trucks HB Schlegel GE Scuseria MA Robb JR

Cheeseman G Scalmani V Barone B Mennucci GA Petersson H Nakatsuji

M Caricato X Li HP Hratchian AF Izmaylov J Bloino G Zheng JL

Sonnenberg M Hada M Ehara K Toyota R Fukuda J Hasegawa M Ishida

T Nakajima Y Honda O Kitao H Nakai T Vreven JA Montgomery Jr JE

Peralta F Ogliaro M Bearpark JJ Heyd E Brothers KN Kudin VN

Staroverov R Kobayashi J Normand K Raghavachari A Rendell JC

Burant SS Iyengar J Tomasi M Cossi N Rega JM Millam M Klene JE

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Knox JB Cross V Bakken C Adamo J Jaramillo R Gomperts RE

Stratmann O Yazyev AJ Austin R Cammi C Pomelli JW Ochterski RL

Martin K Morokuma VG Zakrzewski GA Voth P Salvador JJ

Dannenberg S Dapprich AD Daniels O Farkas JB Foresman JV Ortiz J

Cioslowski DJ Fox GAUSSIAN 09 (Revision A01) Gaussian

IncWallingford CT (2009)

[21] A Brink HG Visser A Roodt Novel imino rhenium(I) tricarbonyl complexes

of salicylidene-derived ligands Synthesis X-ray crystallographic studies

spectroscopic characterization and DFT calculations Polyhedron 52 (2013) 416-

423

[22] J Mukiza TIA Gerber EC Hosten Decarboxylation of 5-amino-orotic acid

and a Schiff base derivative by rhenium(V) Inorg Chem Comm 57 (2015) 54-

57

[23] K Potgieter P Mayer T Gerber N Yumata E Hosten I Booysen R Betz M

Ismail B van Brecht Rhenium(I) tricarbonyl complexes with multidentate

nitrogen-donor derivatives Polyhedron 49 (2013) 67-73

[24] IN Booysen I Ebinumoliseh MP Akerman B Xulu A rhenium(I) compound

bearing a dimerized chromone NO bidentate chelator Inorg Chem Comm 62

(2015) 8-10

[25] P Mayer TIA Gerber B Buyambo A Abrahams Coordination behaviour of

acetylacetone-derived Schiff bases towards rhenium(I) and (V) Polyhedron 28

(2009) 1174-1178

[26] T Jurca O Ramadan I Korobkov DS Richeson Employing sterically

encumbered bis(imino)pyridine ligands in support of fac-rhenium(I) carbonyls

J Organomet Chem 802 (2016) 27-31

[27] J Ho WY Lee KJT Koh PPF Lee YK Yan Rhenium(I) tricarbonyl

complexes of salicylaldehyde semicarbazones Synthesis crystal structures and

cytotoxicity J Inorg Biochem 119 (2013) 10-20

[28] B Machura A Świtlicka M Wolff J Kusz R Kruszynski Mono- and di-

nuclear oxorhenium(V) complexes of 47-diphenyl-110-phenanthroline

Polyhedron 28 (2009) 3999-4009

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[29] B Machura M Jaworska P Lodowski Natural bond orbital analysis and

density functional study of linear and bent oxo-bridged dimers of rhenium(V)

J Mol Struc-Theochem 766 (2006) 1-8

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Highlights

bull Chromone rhenium(I) compounds

bull Simulated IR spectra

bull Low calculated RMSDs

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Fig 2 An ORTEP view of compound 1 showing 50 probability displacement ellipsoids

and the atom labelling The tetrahydrofuran molecules of crystallization were omitted for

clarity

33 Crystal structure of 2

Four molecules of 2 occupies its monoclinic unit cell and each of these

molecules forms dimers with molecules of 2 in adjacent unit cells via classical

hydrogen-bonding interactions [Br1N2A-H2ABr1AN2-H = 257(3) Aring] see Fig

S10 Consequently molecules of 2 are self-assembled in columns aligned with the

[b]-axis Indicative to 1 the constrained bite angle [O1-Re-N1 = 8199(7)ordm] of 2 results

in the deviation of orthogonality in the opposing C17-Re-C19 [8690(1)ordm] bond angle

see Fig 3

The rhenium to halide bonds of 1 [Re1-Br1 = 26455(3) Aring and Re2-Br2 =

26377(3) Aring] and 2 [Re-Br = 26322(8) Aring] are comparable to those found in other facial

tricarbonyl rhenium complexes [26 27] All the remaining coordination bonds of 2

[Re-N1 = 2186(2) Aring Re-O1 = 2141(1) Aring Re-C17 = 1931(2) Aring Re-C18 = 1901(2) Aring

and Re-C19 = 1901(2) Aring] were similar to its chloro-analogue fac-[Re(CO)3(bzch)Cl]

viz Re-Oketone = 2137(2) Aring Re-Nbenzimidazole = 2179(2) Aring and Re-Ccarbonyl = 1929(2) Aring

1904(2) Aring 1898(2) Aring [11] Furthermore the double bond character of the C10-N1

bonds [1336(3) Aring] are clearly established when compared to the C-N bond lengths

[C10-N2 = 1358(3) Aring C16-N1 = 1401(3) Aring and C11-N2 = 1374(3) Aring] In addition the

bridging C9-C10 [1466(3) Aring] bond is single based on the more shorter localized C=C

[1365(3) Aring] chromone bond In turn the degrees of freedom around the C9-10 single

bond allows the chromone and benzimidazole plane to form a dihedral angle of

601ordm Also the benzimidazole and chromone moeities lies out of the plane of the

O1N1C19C17 mean basal plane by 1783ordm and 1837ordm respectively The toluene

molecule of recrystallization from an adjacent unit cell is nearly co-planar with the

bzch chelator of 1 indicating - interactions between this toluene molecule and the

bzch chelator (toluene Csp2 centroid to C9 = 3309 Aring and toluene Csp2 centroid to C10

= 3561 Aring)

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An evaluation of the experimental and optimized geometrical parameters for

the metal complexes reveals that the calculated intraligand bond distances [C17-C18

= 15374 Aring for 1 and C1-C9 = 13601 Aring for 2] and angles [O6-Re2-N3 = 83023ordm for 1

and O1-Re-N1 = 80800ordm for 2] compares well with their analogous experimental

geometrical parameters [C17-C18 = 1537(4) Aring for 1 C1-C9 = 1365(3) Aring for 2 O6-

Re2-N3 = 8393(7)ordm for 1 and O1-Re-N1 = 8199(7)ordm for 2] In addition the differences

in bond lengths found between comparable experimental [eg Re1-C1 = 1942(3) Aring

for 1 and Re-C19 = 1901(2) Aring] and optimized [eg Re1-C1 = 19344 Aring for 1 and Re-

C19 = 19034 Aring for 2] organometallic Re-CO bonds are not significant Discrepencies

found between the experimental [Re1-Br1 = 26455(3) Aring Re2-Br2 = 26377(3) Aring for 1

and Re-Br = 26322(8) Aring for 2] and calculated [Re1-Br1 = 272064 Aring Re2-Br2 = 272059

Aring for 1 and Re-Br = 266556 Aring for 2] rhenium to halide bonds are significant which

are ascribed to the rhenium atoms having lower calculated Natural Population

Analysis charges (0851 for Re12 in 1 and 0889 in 2) than the formal +I charge [28

29] The same trend is observed when examining the Re-Oketonic and Re-N

coordination bonds which were found to be longer in the computational models [eg

Re1-O1 = 21765 Aring Re1-N1 = 22224 Aring for 1 and Re-O1 = 22226 Aring Re-N1 = 23072 Aring

for 2] due to their lower Lewis acidic character of the metal centres than those in the

crystal structures [eg Re1-O1 = 2137(2) Aring Re1-N1 = 2169(2) Aring for 1 and Re-O1 =

2141(2) Aring Re-N1 = 2186(2) Aring for 2]

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Fig 3 An ORTEP view of complex 2 showing 50 probability displacement ellipsoids and

the atom labelling The toluene molecule of crystallization was omitted for clarity

Conclusion

Exploring the coordination behaviours of the diimine chret and chb afforded the di-

and mononuclear rhenium(I) compounds fac-(Re(CO)3Br)2(micro-chret) (1) and fac-

[Re(CO)3(bzch)Br] (2) The interpretation of the IR experimental spectra of the metal

compounds was supported by their simulated spectra calculated at the DFT level of

theory X-ray studies concured with the spectroscopic characterization revealing the

transformation of the chb diimine into the bzch chelator (in 2) and affirming the

coordination modes of the chb (in 1) and bzch (in 2) chelators In addition the 6-

membered chelate rings had a significant influence on the geometrical parameters of

the octahedral geometries of 1 and 2

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Supporting information

CCDC 1451521 and 1451522 contains crystallographic data for this article These data

can be obtained free of charge at wwwccdccamacukcontsretrievinghtml [or

from the Cambridge Crystallographic Data Centre (CCDC) 12 Union Road

Cambridge CB21EZ UK Fax +44(0)1223-336033 Email depositccdccamacuk]

Supplementary figures S1-S10 associated with this article can be found in the online

version

Acknowledgements

We are grateful to the University of KwaZulu-Natal and the National Research

Foundation of South Africa for financial support

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Table 1 Crystal data and structure refinement data

13(C4H8O) 2C7H8

Chemical formula C28H18Br2N4O10Re23(C4H8O) C19H10BrN2O5ReC7H8

Formula weight 131899 70453

TemperatureK 100(2) 100(2)

Crystal system Triclinic Monoclinic

Space group P-1 P21n

Unit cell dimensions (Ǻ deg) a = 128859(6) a = 12400(5)

b = 131199(6) b = 11778(5)

c = 149558(7) c = 16316(5)

α= 114601(2) α = 90000(5)

β = 98138(2) β = 92469(5)

γ = 102350(2) γ = 90000(5)

Crystal size (mm) 013 x 006 x 005 009 x 006 x 005

V(Aring3) 216873 (18) 238007(16)

Z 2 4

Density (calc) (mgm3) 2020 1966

Absorption coefficient (mm-1) 749 682

F(000) 1268 1352

θ range for data collection

(deg)

16 291 20 290

Reflections measured 41497 23824

Observed reflections [Igt2σ(I)] 10414 5621

Independent reflections 11421 6310

DataRestraintsparameters 114210566 56210321

Goodness of fit on F2 103 103

Observed R wR2 0018 0043 0020 0042

Rint 0018 0027

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Table 2 Selected bond lengths [Aring] and bond angles [deg] for 1 The RMSD of 1 is 0720 Aring

Experimental Optimized

Re1-Br1 26455(3) 272064 Re2-Br2 26377(3) 272059 Re1-O1 2137(2) 21765 Re2-O6 2139(2) 21764 Re1-N1 2169(2) 22224 Re2-N3 2171(2) 22224 Re1-C1 1942(3) 19344 Re1-C2 1894(3) 19091 Re1-C3 1897(3) 19071 Re2-C4 1908(3) 19071 Re2-C5 1932(3) 19091 Re2-C6 1893(2) 19343 C16-N1 1286(4) 12919 C19-N3 1291(4) 12919 C14-O1 1259(4) 12502 C28-O6 1261(3) 12503 C1-O3 1144(3) 11492 C8-O2 1383(3) 13796 C21-O7 1347(4) 13440 C7-C15 1414(4) 14102 C20-C21 1411(4) 14103 C17-C18 1537(3) 15374 O1-Re1-N1 8452(7) 83027 O6-Re2-N3 8393(7) 83023 C2-Re1-Br1 17685(8) 177228 O1-Re1-C3 17741(9) 176550 C1-Re1-N1 1762(1) 174310 Br2-Re2-C6 17699(8) 177236 C4-Re2-O6 17641(9) 176545 N3-Re2-C5 1742(1) 174309 C16-N1-C17 1150(2) 114920 C18-N3-C19 1148(2) 114920

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Table 3 Selected bond lengths [Aring] and bond angles [deg] for 2 The RMSD of 2 is 0267 Aring

Experimental Optimized

Re-Br 26322(8) 266556 Re-N1 2186(2) 23072 Re-O1 2141(2) 22226 Re-C17 1931(2) 19263 Re-C18 1901(2) 19150 Re-C19 1901(2) 19034 C9-C10 1466(3) 14608 C1-C9 1365(3) 13601 O1-Re-N1 8199(7) 80800 C17-Re-C19 8690(1) 88380 Br-Re-C18 17582(7) 176266

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References

[1] JR Dilworth SJ Parrott The biomedical chemistry of technetium and

rhenium Chem Soc Rev 27 (1998) 43-55

[2] S Jurisson D Berning J Wei M Dangshe Coordination compounds in

nuclear medicine Chem Rev 93 (1993) 1137-1156

[3] S Juumlrgens WA Herrmann FE Kuumlhn Rhenium and technetium based

radiopharmaceuticals Development and recent advances J Organomet Chem

751 (2014) 83-89

[4] U Abram R Alberto Technetium and Rhenium - Coordination Chemistry and

Nuclear Medical Applications Braz Chem Soc 17 (2006) 1486-1500

[5] SL Binkley TC Leeper RS Rowlett RS Herrick CJ Ziegler

Re(CO)3(H2O)3+ binding to lysozyme structure and reactivity Mettalomics 3

(2011) 909-916

[6] RS Herrick TJ Brunker C Maus K Crandall A Cetin CJ

Ziegler Aqueous preparation and physiological stability studies of

Re(CO)3(tripodal) compounds Chem Commun (2006) 4330-4331

[7] K Potgieter P Mayer TIA Gerber IN Booysen Coordination behaviour of

the multidentate Schiff base 26-bis(2-hydroxyphenyliminomethyl)pyridine

towards the fac-[Re(CO)3]+ and [ReO]3+ cores Polyhedron 28 (2009) 2808-2812

[8] CL Ferreira CB Ewart SR Bayly B O Patrick J Steele MJ Adam C

Orvig Glucosamine Conjugates of Tricarbonylcyclopentadienyl Rhenium(I)

and Technetium(I) Cores Inorg Chem 45 (2006) 6979-6987

[9] Q Nadeem D Can Y Shen M Felber Z Mahmooda R Alberto Synthesis of

tripeptide derivatized cyclopentadienyl complexes of technetium and rhenium

as radiopharmaceutical probes Org Biomol Chem 12 (2014) 1966-1974

[10] IN Booysen M Ismail TIA Gerber M Akerman B Van Brecht Oxo and

oxofree rhenium(V) complexes with NO-donor Schiff bases S Afr J Chem 65

(2012) 174-177

[11] IN Booysen MB Ismail OQ Munro Mono- and dinuclear rhenium(I)

compounds with bidentate benzimidazole chelators Inorg Chem Commun 30

(2013) 168-172

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[12] IN Booysen MB Ismail MP Akerman Coordination behaviour of chromone

Schiff bases towards the [ReVO]3+ and [ReI(CO)3]+ cores J Coord Chem 66

(2013) 4371-4386

[13] S Bhatnagar S Sahir P Kackar S Kaushik MK Dave A Shukla A Goel

Synthesis and docking studies on styryl chromones exhibiting cytotoxicity in

human breast cancer cell line Bioorg Med Chem Lett 20 (2010) 4945-4950

[14] M Recanatini A Bisi A Cavalli F Belluti S Gobbi A Rampa P Valenti M

Palzer A Palusczak RW Hartmann A New Class of Nonsteroidal Aromatase

Inhibitorsthinsp Design and Synthesis of Chromone and Xanthone Derivatives and

Inhibition of the P450 Enzymes Aromatase and 17α-HydroxylaseC1720-

Lyase J Med Chem 44 (2001) 672-680

[15] IN Booysen A Adebisi MP Akerman OQ Munro B Xulu Coordination of

di- and triimine ligands at ruthenium(II) and ruthenium(III) centers structural

electrochemical and radical scavenging studies J Coord Chem (2016) doi

1010800095897220161177177

[16] Bruker APEX2 SAINT and SADABS Bruker AXS Inc (2010) Madison

Wisconsin USA

[17] RH Blessing An empirical correction for absorption anisotropy Acta Cryst

A51 (1995) 33-38

[18] GM Sheldrick A short history of SHELX Acta Cryst A64 (2008) 112-122

[19] LJ Farrugia WinGX and ORTEP for Windows an update J Appl Cryst 45

(2012) 849-854

[20] MJ Frisch GW Trucks HB Schlegel GE Scuseria MA Robb JR

Cheeseman G Scalmani V Barone B Mennucci GA Petersson H Nakatsuji

M Caricato X Li HP Hratchian AF Izmaylov J Bloino G Zheng JL

Sonnenberg M Hada M Ehara K Toyota R Fukuda J Hasegawa M Ishida

T Nakajima Y Honda O Kitao H Nakai T Vreven JA Montgomery Jr JE

Peralta F Ogliaro M Bearpark JJ Heyd E Brothers KN Kudin VN

Staroverov R Kobayashi J Normand K Raghavachari A Rendell JC

Burant SS Iyengar J Tomasi M Cossi N Rega JM Millam M Klene JE

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Knox JB Cross V Bakken C Adamo J Jaramillo R Gomperts RE

Stratmann O Yazyev AJ Austin R Cammi C Pomelli JW Ochterski RL

Martin K Morokuma VG Zakrzewski GA Voth P Salvador JJ

Dannenberg S Dapprich AD Daniels O Farkas JB Foresman JV Ortiz J

Cioslowski DJ Fox GAUSSIAN 09 (Revision A01) Gaussian

IncWallingford CT (2009)

[21] A Brink HG Visser A Roodt Novel imino rhenium(I) tricarbonyl complexes

of salicylidene-derived ligands Synthesis X-ray crystallographic studies

spectroscopic characterization and DFT calculations Polyhedron 52 (2013) 416-

423

[22] J Mukiza TIA Gerber EC Hosten Decarboxylation of 5-amino-orotic acid

and a Schiff base derivative by rhenium(V) Inorg Chem Comm 57 (2015) 54-

57

[23] K Potgieter P Mayer T Gerber N Yumata E Hosten I Booysen R Betz M

Ismail B van Brecht Rhenium(I) tricarbonyl complexes with multidentate

nitrogen-donor derivatives Polyhedron 49 (2013) 67-73

[24] IN Booysen I Ebinumoliseh MP Akerman B Xulu A rhenium(I) compound

bearing a dimerized chromone NO bidentate chelator Inorg Chem Comm 62

(2015) 8-10

[25] P Mayer TIA Gerber B Buyambo A Abrahams Coordination behaviour of

acetylacetone-derived Schiff bases towards rhenium(I) and (V) Polyhedron 28

(2009) 1174-1178

[26] T Jurca O Ramadan I Korobkov DS Richeson Employing sterically

encumbered bis(imino)pyridine ligands in support of fac-rhenium(I) carbonyls

J Organomet Chem 802 (2016) 27-31

[27] J Ho WY Lee KJT Koh PPF Lee YK Yan Rhenium(I) tricarbonyl

complexes of salicylaldehyde semicarbazones Synthesis crystal structures and

cytotoxicity J Inorg Biochem 119 (2013) 10-20

[28] B Machura A Świtlicka M Wolff J Kusz R Kruszynski Mono- and di-

nuclear oxorhenium(V) complexes of 47-diphenyl-110-phenanthroline

Polyhedron 28 (2009) 3999-4009

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[29] B Machura M Jaworska P Lodowski Natural bond orbital analysis and

density functional study of linear and bent oxo-bridged dimers of rhenium(V)

J Mol Struc-Theochem 766 (2006) 1-8

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Highlights

bull Chromone rhenium(I) compounds

bull Simulated IR spectra

bull Low calculated RMSDs

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An evaluation of the experimental and optimized geometrical parameters for

the metal complexes reveals that the calculated intraligand bond distances [C17-C18

= 15374 Aring for 1 and C1-C9 = 13601 Aring for 2] and angles [O6-Re2-N3 = 83023ordm for 1

and O1-Re-N1 = 80800ordm for 2] compares well with their analogous experimental

geometrical parameters [C17-C18 = 1537(4) Aring for 1 C1-C9 = 1365(3) Aring for 2 O6-

Re2-N3 = 8393(7)ordm for 1 and O1-Re-N1 = 8199(7)ordm for 2] In addition the differences

in bond lengths found between comparable experimental [eg Re1-C1 = 1942(3) Aring

for 1 and Re-C19 = 1901(2) Aring] and optimized [eg Re1-C1 = 19344 Aring for 1 and Re-

C19 = 19034 Aring for 2] organometallic Re-CO bonds are not significant Discrepencies

found between the experimental [Re1-Br1 = 26455(3) Aring Re2-Br2 = 26377(3) Aring for 1

and Re-Br = 26322(8) Aring for 2] and calculated [Re1-Br1 = 272064 Aring Re2-Br2 = 272059

Aring for 1 and Re-Br = 266556 Aring for 2] rhenium to halide bonds are significant which

are ascribed to the rhenium atoms having lower calculated Natural Population

Analysis charges (0851 for Re12 in 1 and 0889 in 2) than the formal +I charge [28

29] The same trend is observed when examining the Re-Oketonic and Re-N

coordination bonds which were found to be longer in the computational models [eg

Re1-O1 = 21765 Aring Re1-N1 = 22224 Aring for 1 and Re-O1 = 22226 Aring Re-N1 = 23072 Aring

for 2] due to their lower Lewis acidic character of the metal centres than those in the

crystal structures [eg Re1-O1 = 2137(2) Aring Re1-N1 = 2169(2) Aring for 1 and Re-O1 =

2141(2) Aring Re-N1 = 2186(2) Aring for 2]

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Fig 3 An ORTEP view of complex 2 showing 50 probability displacement ellipsoids and

the atom labelling The toluene molecule of crystallization was omitted for clarity

Conclusion

Exploring the coordination behaviours of the diimine chret and chb afforded the di-

and mononuclear rhenium(I) compounds fac-(Re(CO)3Br)2(micro-chret) (1) and fac-

[Re(CO)3(bzch)Br] (2) The interpretation of the IR experimental spectra of the metal

compounds was supported by their simulated spectra calculated at the DFT level of

theory X-ray studies concured with the spectroscopic characterization revealing the

transformation of the chb diimine into the bzch chelator (in 2) and affirming the

coordination modes of the chb (in 1) and bzch (in 2) chelators In addition the 6-

membered chelate rings had a significant influence on the geometrical parameters of

the octahedral geometries of 1 and 2

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Supporting information

CCDC 1451521 and 1451522 contains crystallographic data for this article These data

can be obtained free of charge at wwwccdccamacukcontsretrievinghtml [or

from the Cambridge Crystallographic Data Centre (CCDC) 12 Union Road

Cambridge CB21EZ UK Fax +44(0)1223-336033 Email depositccdccamacuk]

Supplementary figures S1-S10 associated with this article can be found in the online

version

Acknowledgements

We are grateful to the University of KwaZulu-Natal and the National Research

Foundation of South Africa for financial support

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Table 1 Crystal data and structure refinement data

13(C4H8O) 2C7H8

Chemical formula C28H18Br2N4O10Re23(C4H8O) C19H10BrN2O5ReC7H8

Formula weight 131899 70453

TemperatureK 100(2) 100(2)

Crystal system Triclinic Monoclinic

Space group P-1 P21n

Unit cell dimensions (Ǻ deg) a = 128859(6) a = 12400(5)

b = 131199(6) b = 11778(5)

c = 149558(7) c = 16316(5)

α= 114601(2) α = 90000(5)

β = 98138(2) β = 92469(5)

γ = 102350(2) γ = 90000(5)

Crystal size (mm) 013 x 006 x 005 009 x 006 x 005

V(Aring3) 216873 (18) 238007(16)

Z 2 4

Density (calc) (mgm3) 2020 1966

Absorption coefficient (mm-1) 749 682

F(000) 1268 1352

θ range for data collection

(deg)

16 291 20 290

Reflections measured 41497 23824

Observed reflections [Igt2σ(I)] 10414 5621

Independent reflections 11421 6310

DataRestraintsparameters 114210566 56210321

Goodness of fit on F2 103 103

Observed R wR2 0018 0043 0020 0042

Rint 0018 0027

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Table 2 Selected bond lengths [Aring] and bond angles [deg] for 1 The RMSD of 1 is 0720 Aring

Experimental Optimized

Re1-Br1 26455(3) 272064 Re2-Br2 26377(3) 272059 Re1-O1 2137(2) 21765 Re2-O6 2139(2) 21764 Re1-N1 2169(2) 22224 Re2-N3 2171(2) 22224 Re1-C1 1942(3) 19344 Re1-C2 1894(3) 19091 Re1-C3 1897(3) 19071 Re2-C4 1908(3) 19071 Re2-C5 1932(3) 19091 Re2-C6 1893(2) 19343 C16-N1 1286(4) 12919 C19-N3 1291(4) 12919 C14-O1 1259(4) 12502 C28-O6 1261(3) 12503 C1-O3 1144(3) 11492 C8-O2 1383(3) 13796 C21-O7 1347(4) 13440 C7-C15 1414(4) 14102 C20-C21 1411(4) 14103 C17-C18 1537(3) 15374 O1-Re1-N1 8452(7) 83027 O6-Re2-N3 8393(7) 83023 C2-Re1-Br1 17685(8) 177228 O1-Re1-C3 17741(9) 176550 C1-Re1-N1 1762(1) 174310 Br2-Re2-C6 17699(8) 177236 C4-Re2-O6 17641(9) 176545 N3-Re2-C5 1742(1) 174309 C16-N1-C17 1150(2) 114920 C18-N3-C19 1148(2) 114920

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Table 3 Selected bond lengths [Aring] and bond angles [deg] for 2 The RMSD of 2 is 0267 Aring

Experimental Optimized

Re-Br 26322(8) 266556 Re-N1 2186(2) 23072 Re-O1 2141(2) 22226 Re-C17 1931(2) 19263 Re-C18 1901(2) 19150 Re-C19 1901(2) 19034 C9-C10 1466(3) 14608 C1-C9 1365(3) 13601 O1-Re-N1 8199(7) 80800 C17-Re-C19 8690(1) 88380 Br-Re-C18 17582(7) 176266

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References

[1] JR Dilworth SJ Parrott The biomedical chemistry of technetium and

rhenium Chem Soc Rev 27 (1998) 43-55

[2] S Jurisson D Berning J Wei M Dangshe Coordination compounds in

nuclear medicine Chem Rev 93 (1993) 1137-1156

[3] S Juumlrgens WA Herrmann FE Kuumlhn Rhenium and technetium based

radiopharmaceuticals Development and recent advances J Organomet Chem

751 (2014) 83-89

[4] U Abram R Alberto Technetium and Rhenium - Coordination Chemistry and

Nuclear Medical Applications Braz Chem Soc 17 (2006) 1486-1500

[5] SL Binkley TC Leeper RS Rowlett RS Herrick CJ Ziegler

Re(CO)3(H2O)3+ binding to lysozyme structure and reactivity Mettalomics 3

(2011) 909-916

[6] RS Herrick TJ Brunker C Maus K Crandall A Cetin CJ

Ziegler Aqueous preparation and physiological stability studies of

Re(CO)3(tripodal) compounds Chem Commun (2006) 4330-4331

[7] K Potgieter P Mayer TIA Gerber IN Booysen Coordination behaviour of

the multidentate Schiff base 26-bis(2-hydroxyphenyliminomethyl)pyridine

towards the fac-[Re(CO)3]+ and [ReO]3+ cores Polyhedron 28 (2009) 2808-2812

[8] CL Ferreira CB Ewart SR Bayly B O Patrick J Steele MJ Adam C

Orvig Glucosamine Conjugates of Tricarbonylcyclopentadienyl Rhenium(I)

and Technetium(I) Cores Inorg Chem 45 (2006) 6979-6987

[9] Q Nadeem D Can Y Shen M Felber Z Mahmooda R Alberto Synthesis of

tripeptide derivatized cyclopentadienyl complexes of technetium and rhenium

as radiopharmaceutical probes Org Biomol Chem 12 (2014) 1966-1974

[10] IN Booysen M Ismail TIA Gerber M Akerman B Van Brecht Oxo and

oxofree rhenium(V) complexes with NO-donor Schiff bases S Afr J Chem 65

(2012) 174-177

[11] IN Booysen MB Ismail OQ Munro Mono- and dinuclear rhenium(I)

compounds with bidentate benzimidazole chelators Inorg Chem Commun 30

(2013) 168-172

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[12] IN Booysen MB Ismail MP Akerman Coordination behaviour of chromone

Schiff bases towards the [ReVO]3+ and [ReI(CO)3]+ cores J Coord Chem 66

(2013) 4371-4386

[13] S Bhatnagar S Sahir P Kackar S Kaushik MK Dave A Shukla A Goel

Synthesis and docking studies on styryl chromones exhibiting cytotoxicity in

human breast cancer cell line Bioorg Med Chem Lett 20 (2010) 4945-4950

[14] M Recanatini A Bisi A Cavalli F Belluti S Gobbi A Rampa P Valenti M

Palzer A Palusczak RW Hartmann A New Class of Nonsteroidal Aromatase

Inhibitorsthinsp Design and Synthesis of Chromone and Xanthone Derivatives and

Inhibition of the P450 Enzymes Aromatase and 17α-HydroxylaseC1720-

Lyase J Med Chem 44 (2001) 672-680

[15] IN Booysen A Adebisi MP Akerman OQ Munro B Xulu Coordination of

di- and triimine ligands at ruthenium(II) and ruthenium(III) centers structural

electrochemical and radical scavenging studies J Coord Chem (2016) doi

1010800095897220161177177

[16] Bruker APEX2 SAINT and SADABS Bruker AXS Inc (2010) Madison

Wisconsin USA

[17] RH Blessing An empirical correction for absorption anisotropy Acta Cryst

A51 (1995) 33-38

[18] GM Sheldrick A short history of SHELX Acta Cryst A64 (2008) 112-122

[19] LJ Farrugia WinGX and ORTEP for Windows an update J Appl Cryst 45

(2012) 849-854

[20] MJ Frisch GW Trucks HB Schlegel GE Scuseria MA Robb JR

Cheeseman G Scalmani V Barone B Mennucci GA Petersson H Nakatsuji

M Caricato X Li HP Hratchian AF Izmaylov J Bloino G Zheng JL

Sonnenberg M Hada M Ehara K Toyota R Fukuda J Hasegawa M Ishida

T Nakajima Y Honda O Kitao H Nakai T Vreven JA Montgomery Jr JE

Peralta F Ogliaro M Bearpark JJ Heyd E Brothers KN Kudin VN

Staroverov R Kobayashi J Normand K Raghavachari A Rendell JC

Burant SS Iyengar J Tomasi M Cossi N Rega JM Millam M Klene JE

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Knox JB Cross V Bakken C Adamo J Jaramillo R Gomperts RE

Stratmann O Yazyev AJ Austin R Cammi C Pomelli JW Ochterski RL

Martin K Morokuma VG Zakrzewski GA Voth P Salvador JJ

Dannenberg S Dapprich AD Daniels O Farkas JB Foresman JV Ortiz J

Cioslowski DJ Fox GAUSSIAN 09 (Revision A01) Gaussian

IncWallingford CT (2009)

[21] A Brink HG Visser A Roodt Novel imino rhenium(I) tricarbonyl complexes

of salicylidene-derived ligands Synthesis X-ray crystallographic studies

spectroscopic characterization and DFT calculations Polyhedron 52 (2013) 416-

423

[22] J Mukiza TIA Gerber EC Hosten Decarboxylation of 5-amino-orotic acid

and a Schiff base derivative by rhenium(V) Inorg Chem Comm 57 (2015) 54-

57

[23] K Potgieter P Mayer T Gerber N Yumata E Hosten I Booysen R Betz M

Ismail B van Brecht Rhenium(I) tricarbonyl complexes with multidentate

nitrogen-donor derivatives Polyhedron 49 (2013) 67-73

[24] IN Booysen I Ebinumoliseh MP Akerman B Xulu A rhenium(I) compound

bearing a dimerized chromone NO bidentate chelator Inorg Chem Comm 62

(2015) 8-10

[25] P Mayer TIA Gerber B Buyambo A Abrahams Coordination behaviour of

acetylacetone-derived Schiff bases towards rhenium(I) and (V) Polyhedron 28

(2009) 1174-1178

[26] T Jurca O Ramadan I Korobkov DS Richeson Employing sterically

encumbered bis(imino)pyridine ligands in support of fac-rhenium(I) carbonyls

J Organomet Chem 802 (2016) 27-31

[27] J Ho WY Lee KJT Koh PPF Lee YK Yan Rhenium(I) tricarbonyl

complexes of salicylaldehyde semicarbazones Synthesis crystal structures and

cytotoxicity J Inorg Biochem 119 (2013) 10-20

[28] B Machura A Świtlicka M Wolff J Kusz R Kruszynski Mono- and di-

nuclear oxorhenium(V) complexes of 47-diphenyl-110-phenanthroline

Polyhedron 28 (2009) 3999-4009

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[29] B Machura M Jaworska P Lodowski Natural bond orbital analysis and

density functional study of linear and bent oxo-bridged dimers of rhenium(V)

J Mol Struc-Theochem 766 (2006) 1-8

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Highlights

bull Chromone rhenium(I) compounds

bull Simulated IR spectra

bull Low calculated RMSDs

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Fig 3 An ORTEP view of complex 2 showing 50 probability displacement ellipsoids and

the atom labelling The toluene molecule of crystallization was omitted for clarity

Conclusion

Exploring the coordination behaviours of the diimine chret and chb afforded the di-

and mononuclear rhenium(I) compounds fac-(Re(CO)3Br)2(micro-chret) (1) and fac-

[Re(CO)3(bzch)Br] (2) The interpretation of the IR experimental spectra of the metal

compounds was supported by their simulated spectra calculated at the DFT level of

theory X-ray studies concured with the spectroscopic characterization revealing the

transformation of the chb diimine into the bzch chelator (in 2) and affirming the

coordination modes of the chb (in 1) and bzch (in 2) chelators In addition the 6-

membered chelate rings had a significant influence on the geometrical parameters of

the octahedral geometries of 1 and 2

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Supporting information

CCDC 1451521 and 1451522 contains crystallographic data for this article These data

can be obtained free of charge at wwwccdccamacukcontsretrievinghtml [or

from the Cambridge Crystallographic Data Centre (CCDC) 12 Union Road

Cambridge CB21EZ UK Fax +44(0)1223-336033 Email depositccdccamacuk]

Supplementary figures S1-S10 associated with this article can be found in the online

version

Acknowledgements

We are grateful to the University of KwaZulu-Natal and the National Research

Foundation of South Africa for financial support

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Table 1 Crystal data and structure refinement data

13(C4H8O) 2C7H8

Chemical formula C28H18Br2N4O10Re23(C4H8O) C19H10BrN2O5ReC7H8

Formula weight 131899 70453

TemperatureK 100(2) 100(2)

Crystal system Triclinic Monoclinic

Space group P-1 P21n

Unit cell dimensions (Ǻ deg) a = 128859(6) a = 12400(5)

b = 131199(6) b = 11778(5)

c = 149558(7) c = 16316(5)

α= 114601(2) α = 90000(5)

β = 98138(2) β = 92469(5)

γ = 102350(2) γ = 90000(5)

Crystal size (mm) 013 x 006 x 005 009 x 006 x 005

V(Aring3) 216873 (18) 238007(16)

Z 2 4

Density (calc) (mgm3) 2020 1966

Absorption coefficient (mm-1) 749 682

F(000) 1268 1352

θ range for data collection

(deg)

16 291 20 290

Reflections measured 41497 23824

Observed reflections [Igt2σ(I)] 10414 5621

Independent reflections 11421 6310

DataRestraintsparameters 114210566 56210321

Goodness of fit on F2 103 103

Observed R wR2 0018 0043 0020 0042

Rint 0018 0027

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Table 2 Selected bond lengths [Aring] and bond angles [deg] for 1 The RMSD of 1 is 0720 Aring

Experimental Optimized

Re1-Br1 26455(3) 272064 Re2-Br2 26377(3) 272059 Re1-O1 2137(2) 21765 Re2-O6 2139(2) 21764 Re1-N1 2169(2) 22224 Re2-N3 2171(2) 22224 Re1-C1 1942(3) 19344 Re1-C2 1894(3) 19091 Re1-C3 1897(3) 19071 Re2-C4 1908(3) 19071 Re2-C5 1932(3) 19091 Re2-C6 1893(2) 19343 C16-N1 1286(4) 12919 C19-N3 1291(4) 12919 C14-O1 1259(4) 12502 C28-O6 1261(3) 12503 C1-O3 1144(3) 11492 C8-O2 1383(3) 13796 C21-O7 1347(4) 13440 C7-C15 1414(4) 14102 C20-C21 1411(4) 14103 C17-C18 1537(3) 15374 O1-Re1-N1 8452(7) 83027 O6-Re2-N3 8393(7) 83023 C2-Re1-Br1 17685(8) 177228 O1-Re1-C3 17741(9) 176550 C1-Re1-N1 1762(1) 174310 Br2-Re2-C6 17699(8) 177236 C4-Re2-O6 17641(9) 176545 N3-Re2-C5 1742(1) 174309 C16-N1-C17 1150(2) 114920 C18-N3-C19 1148(2) 114920

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Table 3 Selected bond lengths [Aring] and bond angles [deg] for 2 The RMSD of 2 is 0267 Aring

Experimental Optimized

Re-Br 26322(8) 266556 Re-N1 2186(2) 23072 Re-O1 2141(2) 22226 Re-C17 1931(2) 19263 Re-C18 1901(2) 19150 Re-C19 1901(2) 19034 C9-C10 1466(3) 14608 C1-C9 1365(3) 13601 O1-Re-N1 8199(7) 80800 C17-Re-C19 8690(1) 88380 Br-Re-C18 17582(7) 176266

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References

[1] JR Dilworth SJ Parrott The biomedical chemistry of technetium and

rhenium Chem Soc Rev 27 (1998) 43-55

[2] S Jurisson D Berning J Wei M Dangshe Coordination compounds in

nuclear medicine Chem Rev 93 (1993) 1137-1156

[3] S Juumlrgens WA Herrmann FE Kuumlhn Rhenium and technetium based

radiopharmaceuticals Development and recent advances J Organomet Chem

751 (2014) 83-89

[4] U Abram R Alberto Technetium and Rhenium - Coordination Chemistry and

Nuclear Medical Applications Braz Chem Soc 17 (2006) 1486-1500

[5] SL Binkley TC Leeper RS Rowlett RS Herrick CJ Ziegler

Re(CO)3(H2O)3+ binding to lysozyme structure and reactivity Mettalomics 3

(2011) 909-916

[6] RS Herrick TJ Brunker C Maus K Crandall A Cetin CJ

Ziegler Aqueous preparation and physiological stability studies of

Re(CO)3(tripodal) compounds Chem Commun (2006) 4330-4331

[7] K Potgieter P Mayer TIA Gerber IN Booysen Coordination behaviour of

the multidentate Schiff base 26-bis(2-hydroxyphenyliminomethyl)pyridine

towards the fac-[Re(CO)3]+ and [ReO]3+ cores Polyhedron 28 (2009) 2808-2812

[8] CL Ferreira CB Ewart SR Bayly B O Patrick J Steele MJ Adam C

Orvig Glucosamine Conjugates of Tricarbonylcyclopentadienyl Rhenium(I)

and Technetium(I) Cores Inorg Chem 45 (2006) 6979-6987

[9] Q Nadeem D Can Y Shen M Felber Z Mahmooda R Alberto Synthesis of

tripeptide derivatized cyclopentadienyl complexes of technetium and rhenium

as radiopharmaceutical probes Org Biomol Chem 12 (2014) 1966-1974

[10] IN Booysen M Ismail TIA Gerber M Akerman B Van Brecht Oxo and

oxofree rhenium(V) complexes with NO-donor Schiff bases S Afr J Chem 65

(2012) 174-177

[11] IN Booysen MB Ismail OQ Munro Mono- and dinuclear rhenium(I)

compounds with bidentate benzimidazole chelators Inorg Chem Commun 30

(2013) 168-172

MANUSCRIP

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ACCEPTED

ACCEPTED MANUSCRIPT

[12] IN Booysen MB Ismail MP Akerman Coordination behaviour of chromone

Schiff bases towards the [ReVO]3+ and [ReI(CO)3]+ cores J Coord Chem 66

(2013) 4371-4386

[13] S Bhatnagar S Sahir P Kackar S Kaushik MK Dave A Shukla A Goel

Synthesis and docking studies on styryl chromones exhibiting cytotoxicity in

human breast cancer cell line Bioorg Med Chem Lett 20 (2010) 4945-4950

[14] M Recanatini A Bisi A Cavalli F Belluti S Gobbi A Rampa P Valenti M

Palzer A Palusczak RW Hartmann A New Class of Nonsteroidal Aromatase

Inhibitorsthinsp Design and Synthesis of Chromone and Xanthone Derivatives and

Inhibition of the P450 Enzymes Aromatase and 17α-HydroxylaseC1720-

Lyase J Med Chem 44 (2001) 672-680

[15] IN Booysen A Adebisi MP Akerman OQ Munro B Xulu Coordination of

di- and triimine ligands at ruthenium(II) and ruthenium(III) centers structural

electrochemical and radical scavenging studies J Coord Chem (2016) doi

1010800095897220161177177

[16] Bruker APEX2 SAINT and SADABS Bruker AXS Inc (2010) Madison

Wisconsin USA

[17] RH Blessing An empirical correction for absorption anisotropy Acta Cryst

A51 (1995) 33-38

[18] GM Sheldrick A short history of SHELX Acta Cryst A64 (2008) 112-122

[19] LJ Farrugia WinGX and ORTEP for Windows an update J Appl Cryst 45

(2012) 849-854

[20] MJ Frisch GW Trucks HB Schlegel GE Scuseria MA Robb JR

Cheeseman G Scalmani V Barone B Mennucci GA Petersson H Nakatsuji

M Caricato X Li HP Hratchian AF Izmaylov J Bloino G Zheng JL

Sonnenberg M Hada M Ehara K Toyota R Fukuda J Hasegawa M Ishida

T Nakajima Y Honda O Kitao H Nakai T Vreven JA Montgomery Jr JE

Peralta F Ogliaro M Bearpark JJ Heyd E Brothers KN Kudin VN

Staroverov R Kobayashi J Normand K Raghavachari A Rendell JC

Burant SS Iyengar J Tomasi M Cossi N Rega JM Millam M Klene JE

MANUSCRIP

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Knox JB Cross V Bakken C Adamo J Jaramillo R Gomperts RE

Stratmann O Yazyev AJ Austin R Cammi C Pomelli JW Ochterski RL

Martin K Morokuma VG Zakrzewski GA Voth P Salvador JJ

Dannenberg S Dapprich AD Daniels O Farkas JB Foresman JV Ortiz J

Cioslowski DJ Fox GAUSSIAN 09 (Revision A01) Gaussian

IncWallingford CT (2009)

[21] A Brink HG Visser A Roodt Novel imino rhenium(I) tricarbonyl complexes

of salicylidene-derived ligands Synthesis X-ray crystallographic studies

spectroscopic characterization and DFT calculations Polyhedron 52 (2013) 416-

423

[22] J Mukiza TIA Gerber EC Hosten Decarboxylation of 5-amino-orotic acid

and a Schiff base derivative by rhenium(V) Inorg Chem Comm 57 (2015) 54-

57

[23] K Potgieter P Mayer T Gerber N Yumata E Hosten I Booysen R Betz M

Ismail B van Brecht Rhenium(I) tricarbonyl complexes with multidentate

nitrogen-donor derivatives Polyhedron 49 (2013) 67-73

[24] IN Booysen I Ebinumoliseh MP Akerman B Xulu A rhenium(I) compound

bearing a dimerized chromone NO bidentate chelator Inorg Chem Comm 62

(2015) 8-10

[25] P Mayer TIA Gerber B Buyambo A Abrahams Coordination behaviour of

acetylacetone-derived Schiff bases towards rhenium(I) and (V) Polyhedron 28

(2009) 1174-1178

[26] T Jurca O Ramadan I Korobkov DS Richeson Employing sterically

encumbered bis(imino)pyridine ligands in support of fac-rhenium(I) carbonyls

J Organomet Chem 802 (2016) 27-31

[27] J Ho WY Lee KJT Koh PPF Lee YK Yan Rhenium(I) tricarbonyl

complexes of salicylaldehyde semicarbazones Synthesis crystal structures and

cytotoxicity J Inorg Biochem 119 (2013) 10-20

[28] B Machura A Świtlicka M Wolff J Kusz R Kruszynski Mono- and di-

nuclear oxorhenium(V) complexes of 47-diphenyl-110-phenanthroline

Polyhedron 28 (2009) 3999-4009

MANUSCRIP

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ACCEPTED MANUSCRIPT

[29] B Machura M Jaworska P Lodowski Natural bond orbital analysis and

density functional study of linear and bent oxo-bridged dimers of rhenium(V)

J Mol Struc-Theochem 766 (2006) 1-8

MANUSCRIP

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ACCEPTED MANUSCRIPT

Highlights

bull Chromone rhenium(I) compounds

bull Simulated IR spectra

bull Low calculated RMSDs

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

Supporting information

CCDC 1451521 and 1451522 contains crystallographic data for this article These data

can be obtained free of charge at wwwccdccamacukcontsretrievinghtml [or

from the Cambridge Crystallographic Data Centre (CCDC) 12 Union Road

Cambridge CB21EZ UK Fax +44(0)1223-336033 Email depositccdccamacuk]

Supplementary figures S1-S10 associated with this article can be found in the online

version

Acknowledgements

We are grateful to the University of KwaZulu-Natal and the National Research

Foundation of South Africa for financial support

MANUSCRIP

T

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ACCEPTED MANUSCRIPT

Table 1 Crystal data and structure refinement data

13(C4H8O) 2C7H8

Chemical formula C28H18Br2N4O10Re23(C4H8O) C19H10BrN2O5ReC7H8

Formula weight 131899 70453

TemperatureK 100(2) 100(2)

Crystal system Triclinic Monoclinic

Space group P-1 P21n

Unit cell dimensions (Ǻ deg) a = 128859(6) a = 12400(5)

b = 131199(6) b = 11778(5)

c = 149558(7) c = 16316(5)

α= 114601(2) α = 90000(5)

β = 98138(2) β = 92469(5)

γ = 102350(2) γ = 90000(5)

Crystal size (mm) 013 x 006 x 005 009 x 006 x 005

V(Aring3) 216873 (18) 238007(16)

Z 2 4

Density (calc) (mgm3) 2020 1966

Absorption coefficient (mm-1) 749 682

F(000) 1268 1352

θ range for data collection

(deg)

16 291 20 290

Reflections measured 41497 23824

Observed reflections [Igt2σ(I)] 10414 5621

Independent reflections 11421 6310

DataRestraintsparameters 114210566 56210321

Goodness of fit on F2 103 103

Observed R wR2 0018 0043 0020 0042

Rint 0018 0027

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Table 2 Selected bond lengths [Aring] and bond angles [deg] for 1 The RMSD of 1 is 0720 Aring

Experimental Optimized

Re1-Br1 26455(3) 272064 Re2-Br2 26377(3) 272059 Re1-O1 2137(2) 21765 Re2-O6 2139(2) 21764 Re1-N1 2169(2) 22224 Re2-N3 2171(2) 22224 Re1-C1 1942(3) 19344 Re1-C2 1894(3) 19091 Re1-C3 1897(3) 19071 Re2-C4 1908(3) 19071 Re2-C5 1932(3) 19091 Re2-C6 1893(2) 19343 C16-N1 1286(4) 12919 C19-N3 1291(4) 12919 C14-O1 1259(4) 12502 C28-O6 1261(3) 12503 C1-O3 1144(3) 11492 C8-O2 1383(3) 13796 C21-O7 1347(4) 13440 C7-C15 1414(4) 14102 C20-C21 1411(4) 14103 C17-C18 1537(3) 15374 O1-Re1-N1 8452(7) 83027 O6-Re2-N3 8393(7) 83023 C2-Re1-Br1 17685(8) 177228 O1-Re1-C3 17741(9) 176550 C1-Re1-N1 1762(1) 174310 Br2-Re2-C6 17699(8) 177236 C4-Re2-O6 17641(9) 176545 N3-Re2-C5 1742(1) 174309 C16-N1-C17 1150(2) 114920 C18-N3-C19 1148(2) 114920

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Table 3 Selected bond lengths [Aring] and bond angles [deg] for 2 The RMSD of 2 is 0267 Aring

Experimental Optimized

Re-Br 26322(8) 266556 Re-N1 2186(2) 23072 Re-O1 2141(2) 22226 Re-C17 1931(2) 19263 Re-C18 1901(2) 19150 Re-C19 1901(2) 19034 C9-C10 1466(3) 14608 C1-C9 1365(3) 13601 O1-Re-N1 8199(7) 80800 C17-Re-C19 8690(1) 88380 Br-Re-C18 17582(7) 176266

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References

[1] JR Dilworth SJ Parrott The biomedical chemistry of technetium and

rhenium Chem Soc Rev 27 (1998) 43-55

[2] S Jurisson D Berning J Wei M Dangshe Coordination compounds in

nuclear medicine Chem Rev 93 (1993) 1137-1156

[3] S Juumlrgens WA Herrmann FE Kuumlhn Rhenium and technetium based

radiopharmaceuticals Development and recent advances J Organomet Chem

751 (2014) 83-89

[4] U Abram R Alberto Technetium and Rhenium - Coordination Chemistry and

Nuclear Medical Applications Braz Chem Soc 17 (2006) 1486-1500

[5] SL Binkley TC Leeper RS Rowlett RS Herrick CJ Ziegler

Re(CO)3(H2O)3+ binding to lysozyme structure and reactivity Mettalomics 3

(2011) 909-916

[6] RS Herrick TJ Brunker C Maus K Crandall A Cetin CJ

Ziegler Aqueous preparation and physiological stability studies of

Re(CO)3(tripodal) compounds Chem Commun (2006) 4330-4331

[7] K Potgieter P Mayer TIA Gerber IN Booysen Coordination behaviour of

the multidentate Schiff base 26-bis(2-hydroxyphenyliminomethyl)pyridine

towards the fac-[Re(CO)3]+ and [ReO]3+ cores Polyhedron 28 (2009) 2808-2812

[8] CL Ferreira CB Ewart SR Bayly B O Patrick J Steele MJ Adam C

Orvig Glucosamine Conjugates of Tricarbonylcyclopentadienyl Rhenium(I)

and Technetium(I) Cores Inorg Chem 45 (2006) 6979-6987

[9] Q Nadeem D Can Y Shen M Felber Z Mahmooda R Alberto Synthesis of

tripeptide derivatized cyclopentadienyl complexes of technetium and rhenium

as radiopharmaceutical probes Org Biomol Chem 12 (2014) 1966-1974

[10] IN Booysen M Ismail TIA Gerber M Akerman B Van Brecht Oxo and

oxofree rhenium(V) complexes with NO-donor Schiff bases S Afr J Chem 65

(2012) 174-177

[11] IN Booysen MB Ismail OQ Munro Mono- and dinuclear rhenium(I)

compounds with bidentate benzimidazole chelators Inorg Chem Commun 30

(2013) 168-172

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[12] IN Booysen MB Ismail MP Akerman Coordination behaviour of chromone

Schiff bases towards the [ReVO]3+ and [ReI(CO)3]+ cores J Coord Chem 66

(2013) 4371-4386

[13] S Bhatnagar S Sahir P Kackar S Kaushik MK Dave A Shukla A Goel

Synthesis and docking studies on styryl chromones exhibiting cytotoxicity in

human breast cancer cell line Bioorg Med Chem Lett 20 (2010) 4945-4950

[14] M Recanatini A Bisi A Cavalli F Belluti S Gobbi A Rampa P Valenti M

Palzer A Palusczak RW Hartmann A New Class of Nonsteroidal Aromatase

Inhibitorsthinsp Design and Synthesis of Chromone and Xanthone Derivatives and

Inhibition of the P450 Enzymes Aromatase and 17α-HydroxylaseC1720-

Lyase J Med Chem 44 (2001) 672-680

[15] IN Booysen A Adebisi MP Akerman OQ Munro B Xulu Coordination of

di- and triimine ligands at ruthenium(II) and ruthenium(III) centers structural

electrochemical and radical scavenging studies J Coord Chem (2016) doi

1010800095897220161177177

[16] Bruker APEX2 SAINT and SADABS Bruker AXS Inc (2010) Madison

Wisconsin USA

[17] RH Blessing An empirical correction for absorption anisotropy Acta Cryst

A51 (1995) 33-38

[18] GM Sheldrick A short history of SHELX Acta Cryst A64 (2008) 112-122

[19] LJ Farrugia WinGX and ORTEP for Windows an update J Appl Cryst 45

(2012) 849-854

[20] MJ Frisch GW Trucks HB Schlegel GE Scuseria MA Robb JR

Cheeseman G Scalmani V Barone B Mennucci GA Petersson H Nakatsuji

M Caricato X Li HP Hratchian AF Izmaylov J Bloino G Zheng JL

Sonnenberg M Hada M Ehara K Toyota R Fukuda J Hasegawa M Ishida

T Nakajima Y Honda O Kitao H Nakai T Vreven JA Montgomery Jr JE

Peralta F Ogliaro M Bearpark JJ Heyd E Brothers KN Kudin VN

Staroverov R Kobayashi J Normand K Raghavachari A Rendell JC

Burant SS Iyengar J Tomasi M Cossi N Rega JM Millam M Klene JE

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Knox JB Cross V Bakken C Adamo J Jaramillo R Gomperts RE

Stratmann O Yazyev AJ Austin R Cammi C Pomelli JW Ochterski RL

Martin K Morokuma VG Zakrzewski GA Voth P Salvador JJ

Dannenberg S Dapprich AD Daniels O Farkas JB Foresman JV Ortiz J

Cioslowski DJ Fox GAUSSIAN 09 (Revision A01) Gaussian

IncWallingford CT (2009)

[21] A Brink HG Visser A Roodt Novel imino rhenium(I) tricarbonyl complexes

of salicylidene-derived ligands Synthesis X-ray crystallographic studies

spectroscopic characterization and DFT calculations Polyhedron 52 (2013) 416-

423

[22] J Mukiza TIA Gerber EC Hosten Decarboxylation of 5-amino-orotic acid

and a Schiff base derivative by rhenium(V) Inorg Chem Comm 57 (2015) 54-

57

[23] K Potgieter P Mayer T Gerber N Yumata E Hosten I Booysen R Betz M

Ismail B van Brecht Rhenium(I) tricarbonyl complexes with multidentate

nitrogen-donor derivatives Polyhedron 49 (2013) 67-73

[24] IN Booysen I Ebinumoliseh MP Akerman B Xulu A rhenium(I) compound

bearing a dimerized chromone NO bidentate chelator Inorg Chem Comm 62

(2015) 8-10

[25] P Mayer TIA Gerber B Buyambo A Abrahams Coordination behaviour of

acetylacetone-derived Schiff bases towards rhenium(I) and (V) Polyhedron 28

(2009) 1174-1178

[26] T Jurca O Ramadan I Korobkov DS Richeson Employing sterically

encumbered bis(imino)pyridine ligands in support of fac-rhenium(I) carbonyls

J Organomet Chem 802 (2016) 27-31

[27] J Ho WY Lee KJT Koh PPF Lee YK Yan Rhenium(I) tricarbonyl

complexes of salicylaldehyde semicarbazones Synthesis crystal structures and

cytotoxicity J Inorg Biochem 119 (2013) 10-20

[28] B Machura A Świtlicka M Wolff J Kusz R Kruszynski Mono- and di-

nuclear oxorhenium(V) complexes of 47-diphenyl-110-phenanthroline

Polyhedron 28 (2009) 3999-4009

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[29] B Machura M Jaworska P Lodowski Natural bond orbital analysis and

density functional study of linear and bent oxo-bridged dimers of rhenium(V)

J Mol Struc-Theochem 766 (2006) 1-8

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Highlights

bull Chromone rhenium(I) compounds

bull Simulated IR spectra

bull Low calculated RMSDs

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Table 1 Crystal data and structure refinement data

13(C4H8O) 2C7H8

Chemical formula C28H18Br2N4O10Re23(C4H8O) C19H10BrN2O5ReC7H8

Formula weight 131899 70453

TemperatureK 100(2) 100(2)

Crystal system Triclinic Monoclinic

Space group P-1 P21n

Unit cell dimensions (Ǻ deg) a = 128859(6) a = 12400(5)

b = 131199(6) b = 11778(5)

c = 149558(7) c = 16316(5)

α= 114601(2) α = 90000(5)

β = 98138(2) β = 92469(5)

γ = 102350(2) γ = 90000(5)

Crystal size (mm) 013 x 006 x 005 009 x 006 x 005

V(Aring3) 216873 (18) 238007(16)

Z 2 4

Density (calc) (mgm3) 2020 1966

Absorption coefficient (mm-1) 749 682

F(000) 1268 1352

θ range for data collection

(deg)

16 291 20 290

Reflections measured 41497 23824

Observed reflections [Igt2σ(I)] 10414 5621

Independent reflections 11421 6310

DataRestraintsparameters 114210566 56210321

Goodness of fit on F2 103 103

Observed R wR2 0018 0043 0020 0042

Rint 0018 0027

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Table 2 Selected bond lengths [Aring] and bond angles [deg] for 1 The RMSD of 1 is 0720 Aring

Experimental Optimized

Re1-Br1 26455(3) 272064 Re2-Br2 26377(3) 272059 Re1-O1 2137(2) 21765 Re2-O6 2139(2) 21764 Re1-N1 2169(2) 22224 Re2-N3 2171(2) 22224 Re1-C1 1942(3) 19344 Re1-C2 1894(3) 19091 Re1-C3 1897(3) 19071 Re2-C4 1908(3) 19071 Re2-C5 1932(3) 19091 Re2-C6 1893(2) 19343 C16-N1 1286(4) 12919 C19-N3 1291(4) 12919 C14-O1 1259(4) 12502 C28-O6 1261(3) 12503 C1-O3 1144(3) 11492 C8-O2 1383(3) 13796 C21-O7 1347(4) 13440 C7-C15 1414(4) 14102 C20-C21 1411(4) 14103 C17-C18 1537(3) 15374 O1-Re1-N1 8452(7) 83027 O6-Re2-N3 8393(7) 83023 C2-Re1-Br1 17685(8) 177228 O1-Re1-C3 17741(9) 176550 C1-Re1-N1 1762(1) 174310 Br2-Re2-C6 17699(8) 177236 C4-Re2-O6 17641(9) 176545 N3-Re2-C5 1742(1) 174309 C16-N1-C17 1150(2) 114920 C18-N3-C19 1148(2) 114920

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Table 3 Selected bond lengths [Aring] and bond angles [deg] for 2 The RMSD of 2 is 0267 Aring

Experimental Optimized

Re-Br 26322(8) 266556 Re-N1 2186(2) 23072 Re-O1 2141(2) 22226 Re-C17 1931(2) 19263 Re-C18 1901(2) 19150 Re-C19 1901(2) 19034 C9-C10 1466(3) 14608 C1-C9 1365(3) 13601 O1-Re-N1 8199(7) 80800 C17-Re-C19 8690(1) 88380 Br-Re-C18 17582(7) 176266

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References

[1] JR Dilworth SJ Parrott The biomedical chemistry of technetium and

rhenium Chem Soc Rev 27 (1998) 43-55

[2] S Jurisson D Berning J Wei M Dangshe Coordination compounds in

nuclear medicine Chem Rev 93 (1993) 1137-1156

[3] S Juumlrgens WA Herrmann FE Kuumlhn Rhenium and technetium based

radiopharmaceuticals Development and recent advances J Organomet Chem

751 (2014) 83-89

[4] U Abram R Alberto Technetium and Rhenium - Coordination Chemistry and

Nuclear Medical Applications Braz Chem Soc 17 (2006) 1486-1500

[5] SL Binkley TC Leeper RS Rowlett RS Herrick CJ Ziegler

Re(CO)3(H2O)3+ binding to lysozyme structure and reactivity Mettalomics 3

(2011) 909-916

[6] RS Herrick TJ Brunker C Maus K Crandall A Cetin CJ

Ziegler Aqueous preparation and physiological stability studies of

Re(CO)3(tripodal) compounds Chem Commun (2006) 4330-4331

[7] K Potgieter P Mayer TIA Gerber IN Booysen Coordination behaviour of

the multidentate Schiff base 26-bis(2-hydroxyphenyliminomethyl)pyridine

towards the fac-[Re(CO)3]+ and [ReO]3+ cores Polyhedron 28 (2009) 2808-2812

[8] CL Ferreira CB Ewart SR Bayly B O Patrick J Steele MJ Adam C

Orvig Glucosamine Conjugates of Tricarbonylcyclopentadienyl Rhenium(I)

and Technetium(I) Cores Inorg Chem 45 (2006) 6979-6987

[9] Q Nadeem D Can Y Shen M Felber Z Mahmooda R Alberto Synthesis of

tripeptide derivatized cyclopentadienyl complexes of technetium and rhenium

as radiopharmaceutical probes Org Biomol Chem 12 (2014) 1966-1974

[10] IN Booysen M Ismail TIA Gerber M Akerman B Van Brecht Oxo and

oxofree rhenium(V) complexes with NO-donor Schiff bases S Afr J Chem 65

(2012) 174-177

[11] IN Booysen MB Ismail OQ Munro Mono- and dinuclear rhenium(I)

compounds with bidentate benzimidazole chelators Inorg Chem Commun 30

(2013) 168-172

MANUSCRIP

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ACCEPTED

ACCEPTED MANUSCRIPT

[12] IN Booysen MB Ismail MP Akerman Coordination behaviour of chromone

Schiff bases towards the [ReVO]3+ and [ReI(CO)3]+ cores J Coord Chem 66

(2013) 4371-4386

[13] S Bhatnagar S Sahir P Kackar S Kaushik MK Dave A Shukla A Goel

Synthesis and docking studies on styryl chromones exhibiting cytotoxicity in

human breast cancer cell line Bioorg Med Chem Lett 20 (2010) 4945-4950

[14] M Recanatini A Bisi A Cavalli F Belluti S Gobbi A Rampa P Valenti M

Palzer A Palusczak RW Hartmann A New Class of Nonsteroidal Aromatase

Inhibitorsthinsp Design and Synthesis of Chromone and Xanthone Derivatives and

Inhibition of the P450 Enzymes Aromatase and 17α-HydroxylaseC1720-

Lyase J Med Chem 44 (2001) 672-680

[15] IN Booysen A Adebisi MP Akerman OQ Munro B Xulu Coordination of

di- and triimine ligands at ruthenium(II) and ruthenium(III) centers structural

electrochemical and radical scavenging studies J Coord Chem (2016) doi

1010800095897220161177177

[16] Bruker APEX2 SAINT and SADABS Bruker AXS Inc (2010) Madison

Wisconsin USA

[17] RH Blessing An empirical correction for absorption anisotropy Acta Cryst

A51 (1995) 33-38

[18] GM Sheldrick A short history of SHELX Acta Cryst A64 (2008) 112-122

[19] LJ Farrugia WinGX and ORTEP for Windows an update J Appl Cryst 45

(2012) 849-854

[20] MJ Frisch GW Trucks HB Schlegel GE Scuseria MA Robb JR

Cheeseman G Scalmani V Barone B Mennucci GA Petersson H Nakatsuji

M Caricato X Li HP Hratchian AF Izmaylov J Bloino G Zheng JL

Sonnenberg M Hada M Ehara K Toyota R Fukuda J Hasegawa M Ishida

T Nakajima Y Honda O Kitao H Nakai T Vreven JA Montgomery Jr JE

Peralta F Ogliaro M Bearpark JJ Heyd E Brothers KN Kudin VN

Staroverov R Kobayashi J Normand K Raghavachari A Rendell JC

Burant SS Iyengar J Tomasi M Cossi N Rega JM Millam M Klene JE

MANUSCRIP

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ACCEPTED

ACCEPTED MANUSCRIPT

Knox JB Cross V Bakken C Adamo J Jaramillo R Gomperts RE

Stratmann O Yazyev AJ Austin R Cammi C Pomelli JW Ochterski RL

Martin K Morokuma VG Zakrzewski GA Voth P Salvador JJ

Dannenberg S Dapprich AD Daniels O Farkas JB Foresman JV Ortiz J

Cioslowski DJ Fox GAUSSIAN 09 (Revision A01) Gaussian

IncWallingford CT (2009)

[21] A Brink HG Visser A Roodt Novel imino rhenium(I) tricarbonyl complexes

of salicylidene-derived ligands Synthesis X-ray crystallographic studies

spectroscopic characterization and DFT calculations Polyhedron 52 (2013) 416-

423

[22] J Mukiza TIA Gerber EC Hosten Decarboxylation of 5-amino-orotic acid

and a Schiff base derivative by rhenium(V) Inorg Chem Comm 57 (2015) 54-

57

[23] K Potgieter P Mayer T Gerber N Yumata E Hosten I Booysen R Betz M

Ismail B van Brecht Rhenium(I) tricarbonyl complexes with multidentate

nitrogen-donor derivatives Polyhedron 49 (2013) 67-73

[24] IN Booysen I Ebinumoliseh MP Akerman B Xulu A rhenium(I) compound

bearing a dimerized chromone NO bidentate chelator Inorg Chem Comm 62

(2015) 8-10

[25] P Mayer TIA Gerber B Buyambo A Abrahams Coordination behaviour of

acetylacetone-derived Schiff bases towards rhenium(I) and (V) Polyhedron 28

(2009) 1174-1178

[26] T Jurca O Ramadan I Korobkov DS Richeson Employing sterically

encumbered bis(imino)pyridine ligands in support of fac-rhenium(I) carbonyls

J Organomet Chem 802 (2016) 27-31

[27] J Ho WY Lee KJT Koh PPF Lee YK Yan Rhenium(I) tricarbonyl

complexes of salicylaldehyde semicarbazones Synthesis crystal structures and

cytotoxicity J Inorg Biochem 119 (2013) 10-20

[28] B Machura A Świtlicka M Wolff J Kusz R Kruszynski Mono- and di-

nuclear oxorhenium(V) complexes of 47-diphenyl-110-phenanthroline

Polyhedron 28 (2009) 3999-4009

MANUSCRIP

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ACCEPTED

ACCEPTED MANUSCRIPT

[29] B Machura M Jaworska P Lodowski Natural bond orbital analysis and

density functional study of linear and bent oxo-bridged dimers of rhenium(V)

J Mol Struc-Theochem 766 (2006) 1-8

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

Highlights

bull Chromone rhenium(I) compounds

bull Simulated IR spectra

bull Low calculated RMSDs

MANUSCRIP

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ACCEPTED MANUSCRIPT

Table 2 Selected bond lengths [Aring] and bond angles [deg] for 1 The RMSD of 1 is 0720 Aring

Experimental Optimized

Re1-Br1 26455(3) 272064 Re2-Br2 26377(3) 272059 Re1-O1 2137(2) 21765 Re2-O6 2139(2) 21764 Re1-N1 2169(2) 22224 Re2-N3 2171(2) 22224 Re1-C1 1942(3) 19344 Re1-C2 1894(3) 19091 Re1-C3 1897(3) 19071 Re2-C4 1908(3) 19071 Re2-C5 1932(3) 19091 Re2-C6 1893(2) 19343 C16-N1 1286(4) 12919 C19-N3 1291(4) 12919 C14-O1 1259(4) 12502 C28-O6 1261(3) 12503 C1-O3 1144(3) 11492 C8-O2 1383(3) 13796 C21-O7 1347(4) 13440 C7-C15 1414(4) 14102 C20-C21 1411(4) 14103 C17-C18 1537(3) 15374 O1-Re1-N1 8452(7) 83027 O6-Re2-N3 8393(7) 83023 C2-Re1-Br1 17685(8) 177228 O1-Re1-C3 17741(9) 176550 C1-Re1-N1 1762(1) 174310 Br2-Re2-C6 17699(8) 177236 C4-Re2-O6 17641(9) 176545 N3-Re2-C5 1742(1) 174309 C16-N1-C17 1150(2) 114920 C18-N3-C19 1148(2) 114920

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ACCEPTED MANUSCRIPT

Table 3 Selected bond lengths [Aring] and bond angles [deg] for 2 The RMSD of 2 is 0267 Aring

Experimental Optimized

Re-Br 26322(8) 266556 Re-N1 2186(2) 23072 Re-O1 2141(2) 22226 Re-C17 1931(2) 19263 Re-C18 1901(2) 19150 Re-C19 1901(2) 19034 C9-C10 1466(3) 14608 C1-C9 1365(3) 13601 O1-Re-N1 8199(7) 80800 C17-Re-C19 8690(1) 88380 Br-Re-C18 17582(7) 176266

MANUSCRIP

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ACCEPTED MANUSCRIPT

References

[1] JR Dilworth SJ Parrott The biomedical chemistry of technetium and

rhenium Chem Soc Rev 27 (1998) 43-55

[2] S Jurisson D Berning J Wei M Dangshe Coordination compounds in

nuclear medicine Chem Rev 93 (1993) 1137-1156

[3] S Juumlrgens WA Herrmann FE Kuumlhn Rhenium and technetium based

radiopharmaceuticals Development and recent advances J Organomet Chem

751 (2014) 83-89

[4] U Abram R Alberto Technetium and Rhenium - Coordination Chemistry and

Nuclear Medical Applications Braz Chem Soc 17 (2006) 1486-1500

[5] SL Binkley TC Leeper RS Rowlett RS Herrick CJ Ziegler

Re(CO)3(H2O)3+ binding to lysozyme structure and reactivity Mettalomics 3

(2011) 909-916

[6] RS Herrick TJ Brunker C Maus K Crandall A Cetin CJ

Ziegler Aqueous preparation and physiological stability studies of

Re(CO)3(tripodal) compounds Chem Commun (2006) 4330-4331

[7] K Potgieter P Mayer TIA Gerber IN Booysen Coordination behaviour of

the multidentate Schiff base 26-bis(2-hydroxyphenyliminomethyl)pyridine

towards the fac-[Re(CO)3]+ and [ReO]3+ cores Polyhedron 28 (2009) 2808-2812

[8] CL Ferreira CB Ewart SR Bayly B O Patrick J Steele MJ Adam C

Orvig Glucosamine Conjugates of Tricarbonylcyclopentadienyl Rhenium(I)

and Technetium(I) Cores Inorg Chem 45 (2006) 6979-6987

[9] Q Nadeem D Can Y Shen M Felber Z Mahmooda R Alberto Synthesis of

tripeptide derivatized cyclopentadienyl complexes of technetium and rhenium

as radiopharmaceutical probes Org Biomol Chem 12 (2014) 1966-1974

[10] IN Booysen M Ismail TIA Gerber M Akerman B Van Brecht Oxo and

oxofree rhenium(V) complexes with NO-donor Schiff bases S Afr J Chem 65

(2012) 174-177

[11] IN Booysen MB Ismail OQ Munro Mono- and dinuclear rhenium(I)

compounds with bidentate benzimidazole chelators Inorg Chem Commun 30

(2013) 168-172

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

[12] IN Booysen MB Ismail MP Akerman Coordination behaviour of chromone

Schiff bases towards the [ReVO]3+ and [ReI(CO)3]+ cores J Coord Chem 66

(2013) 4371-4386

[13] S Bhatnagar S Sahir P Kackar S Kaushik MK Dave A Shukla A Goel

Synthesis and docking studies on styryl chromones exhibiting cytotoxicity in

human breast cancer cell line Bioorg Med Chem Lett 20 (2010) 4945-4950

[14] M Recanatini A Bisi A Cavalli F Belluti S Gobbi A Rampa P Valenti M

Palzer A Palusczak RW Hartmann A New Class of Nonsteroidal Aromatase

Inhibitorsthinsp Design and Synthesis of Chromone and Xanthone Derivatives and

Inhibition of the P450 Enzymes Aromatase and 17α-HydroxylaseC1720-

Lyase J Med Chem 44 (2001) 672-680

[15] IN Booysen A Adebisi MP Akerman OQ Munro B Xulu Coordination of

di- and triimine ligands at ruthenium(II) and ruthenium(III) centers structural

electrochemical and radical scavenging studies J Coord Chem (2016) doi

1010800095897220161177177

[16] Bruker APEX2 SAINT and SADABS Bruker AXS Inc (2010) Madison

Wisconsin USA

[17] RH Blessing An empirical correction for absorption anisotropy Acta Cryst

A51 (1995) 33-38

[18] GM Sheldrick A short history of SHELX Acta Cryst A64 (2008) 112-122

[19] LJ Farrugia WinGX and ORTEP for Windows an update J Appl Cryst 45

(2012) 849-854

[20] MJ Frisch GW Trucks HB Schlegel GE Scuseria MA Robb JR

Cheeseman G Scalmani V Barone B Mennucci GA Petersson H Nakatsuji

M Caricato X Li HP Hratchian AF Izmaylov J Bloino G Zheng JL

Sonnenberg M Hada M Ehara K Toyota R Fukuda J Hasegawa M Ishida

T Nakajima Y Honda O Kitao H Nakai T Vreven JA Montgomery Jr JE

Peralta F Ogliaro M Bearpark JJ Heyd E Brothers KN Kudin VN

Staroverov R Kobayashi J Normand K Raghavachari A Rendell JC

Burant SS Iyengar J Tomasi M Cossi N Rega JM Millam M Klene JE

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

Knox JB Cross V Bakken C Adamo J Jaramillo R Gomperts RE

Stratmann O Yazyev AJ Austin R Cammi C Pomelli JW Ochterski RL

Martin K Morokuma VG Zakrzewski GA Voth P Salvador JJ

Dannenberg S Dapprich AD Daniels O Farkas JB Foresman JV Ortiz J

Cioslowski DJ Fox GAUSSIAN 09 (Revision A01) Gaussian

IncWallingford CT (2009)

[21] A Brink HG Visser A Roodt Novel imino rhenium(I) tricarbonyl complexes

of salicylidene-derived ligands Synthesis X-ray crystallographic studies

spectroscopic characterization and DFT calculations Polyhedron 52 (2013) 416-

423

[22] J Mukiza TIA Gerber EC Hosten Decarboxylation of 5-amino-orotic acid

and a Schiff base derivative by rhenium(V) Inorg Chem Comm 57 (2015) 54-

57

[23] K Potgieter P Mayer T Gerber N Yumata E Hosten I Booysen R Betz M

Ismail B van Brecht Rhenium(I) tricarbonyl complexes with multidentate

nitrogen-donor derivatives Polyhedron 49 (2013) 67-73

[24] IN Booysen I Ebinumoliseh MP Akerman B Xulu A rhenium(I) compound

bearing a dimerized chromone NO bidentate chelator Inorg Chem Comm 62

(2015) 8-10

[25] P Mayer TIA Gerber B Buyambo A Abrahams Coordination behaviour of

acetylacetone-derived Schiff bases towards rhenium(I) and (V) Polyhedron 28

(2009) 1174-1178

[26] T Jurca O Ramadan I Korobkov DS Richeson Employing sterically

encumbered bis(imino)pyridine ligands in support of fac-rhenium(I) carbonyls

J Organomet Chem 802 (2016) 27-31

[27] J Ho WY Lee KJT Koh PPF Lee YK Yan Rhenium(I) tricarbonyl

complexes of salicylaldehyde semicarbazones Synthesis crystal structures and

cytotoxicity J Inorg Biochem 119 (2013) 10-20

[28] B Machura A Świtlicka M Wolff J Kusz R Kruszynski Mono- and di-

nuclear oxorhenium(V) complexes of 47-diphenyl-110-phenanthroline

Polyhedron 28 (2009) 3999-4009

MANUSCRIP

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[29] B Machura M Jaworska P Lodowski Natural bond orbital analysis and

density functional study of linear and bent oxo-bridged dimers of rhenium(V)

J Mol Struc-Theochem 766 (2006) 1-8

MANUSCRIP

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ACCEPTED MANUSCRIPT

Highlights

bull Chromone rhenium(I) compounds

bull Simulated IR spectra

bull Low calculated RMSDs

MANUSCRIP

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Table 3 Selected bond lengths [Aring] and bond angles [deg] for 2 The RMSD of 2 is 0267 Aring

Experimental Optimized

Re-Br 26322(8) 266556 Re-N1 2186(2) 23072 Re-O1 2141(2) 22226 Re-C17 1931(2) 19263 Re-C18 1901(2) 19150 Re-C19 1901(2) 19034 C9-C10 1466(3) 14608 C1-C9 1365(3) 13601 O1-Re-N1 8199(7) 80800 C17-Re-C19 8690(1) 88380 Br-Re-C18 17582(7) 176266

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References

[1] JR Dilworth SJ Parrott The biomedical chemistry of technetium and

rhenium Chem Soc Rev 27 (1998) 43-55

[2] S Jurisson D Berning J Wei M Dangshe Coordination compounds in

nuclear medicine Chem Rev 93 (1993) 1137-1156

[3] S Juumlrgens WA Herrmann FE Kuumlhn Rhenium and technetium based

radiopharmaceuticals Development and recent advances J Organomet Chem

751 (2014) 83-89

[4] U Abram R Alberto Technetium and Rhenium - Coordination Chemistry and

Nuclear Medical Applications Braz Chem Soc 17 (2006) 1486-1500

[5] SL Binkley TC Leeper RS Rowlett RS Herrick CJ Ziegler

Re(CO)3(H2O)3+ binding to lysozyme structure and reactivity Mettalomics 3

(2011) 909-916

[6] RS Herrick TJ Brunker C Maus K Crandall A Cetin CJ

Ziegler Aqueous preparation and physiological stability studies of

Re(CO)3(tripodal) compounds Chem Commun (2006) 4330-4331

[7] K Potgieter P Mayer TIA Gerber IN Booysen Coordination behaviour of

the multidentate Schiff base 26-bis(2-hydroxyphenyliminomethyl)pyridine

towards the fac-[Re(CO)3]+ and [ReO]3+ cores Polyhedron 28 (2009) 2808-2812

[8] CL Ferreira CB Ewart SR Bayly B O Patrick J Steele MJ Adam C

Orvig Glucosamine Conjugates of Tricarbonylcyclopentadienyl Rhenium(I)

and Technetium(I) Cores Inorg Chem 45 (2006) 6979-6987

[9] Q Nadeem D Can Y Shen M Felber Z Mahmooda R Alberto Synthesis of

tripeptide derivatized cyclopentadienyl complexes of technetium and rhenium

as radiopharmaceutical probes Org Biomol Chem 12 (2014) 1966-1974

[10] IN Booysen M Ismail TIA Gerber M Akerman B Van Brecht Oxo and

oxofree rhenium(V) complexes with NO-donor Schiff bases S Afr J Chem 65

(2012) 174-177

[11] IN Booysen MB Ismail OQ Munro Mono- and dinuclear rhenium(I)

compounds with bidentate benzimidazole chelators Inorg Chem Commun 30

(2013) 168-172

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

[12] IN Booysen MB Ismail MP Akerman Coordination behaviour of chromone

Schiff bases towards the [ReVO]3+ and [ReI(CO)3]+ cores J Coord Chem 66

(2013) 4371-4386

[13] S Bhatnagar S Sahir P Kackar S Kaushik MK Dave A Shukla A Goel

Synthesis and docking studies on styryl chromones exhibiting cytotoxicity in

human breast cancer cell line Bioorg Med Chem Lett 20 (2010) 4945-4950

[14] M Recanatini A Bisi A Cavalli F Belluti S Gobbi A Rampa P Valenti M

Palzer A Palusczak RW Hartmann A New Class of Nonsteroidal Aromatase

Inhibitorsthinsp Design and Synthesis of Chromone and Xanthone Derivatives and

Inhibition of the P450 Enzymes Aromatase and 17α-HydroxylaseC1720-

Lyase J Med Chem 44 (2001) 672-680

[15] IN Booysen A Adebisi MP Akerman OQ Munro B Xulu Coordination of

di- and triimine ligands at ruthenium(II) and ruthenium(III) centers structural

electrochemical and radical scavenging studies J Coord Chem (2016) doi

1010800095897220161177177

[16] Bruker APEX2 SAINT and SADABS Bruker AXS Inc (2010) Madison

Wisconsin USA

[17] RH Blessing An empirical correction for absorption anisotropy Acta Cryst

A51 (1995) 33-38

[18] GM Sheldrick A short history of SHELX Acta Cryst A64 (2008) 112-122

[19] LJ Farrugia WinGX and ORTEP for Windows an update J Appl Cryst 45

(2012) 849-854

[20] MJ Frisch GW Trucks HB Schlegel GE Scuseria MA Robb JR

Cheeseman G Scalmani V Barone B Mennucci GA Petersson H Nakatsuji

M Caricato X Li HP Hratchian AF Izmaylov J Bloino G Zheng JL

Sonnenberg M Hada M Ehara K Toyota R Fukuda J Hasegawa M Ishida

T Nakajima Y Honda O Kitao H Nakai T Vreven JA Montgomery Jr JE

Peralta F Ogliaro M Bearpark JJ Heyd E Brothers KN Kudin VN

Staroverov R Kobayashi J Normand K Raghavachari A Rendell JC

Burant SS Iyengar J Tomasi M Cossi N Rega JM Millam M Klene JE

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

Knox JB Cross V Bakken C Adamo J Jaramillo R Gomperts RE

Stratmann O Yazyev AJ Austin R Cammi C Pomelli JW Ochterski RL

Martin K Morokuma VG Zakrzewski GA Voth P Salvador JJ

Dannenberg S Dapprich AD Daniels O Farkas JB Foresman JV Ortiz J

Cioslowski DJ Fox GAUSSIAN 09 (Revision A01) Gaussian

IncWallingford CT (2009)

[21] A Brink HG Visser A Roodt Novel imino rhenium(I) tricarbonyl complexes

of salicylidene-derived ligands Synthesis X-ray crystallographic studies

spectroscopic characterization and DFT calculations Polyhedron 52 (2013) 416-

423

[22] J Mukiza TIA Gerber EC Hosten Decarboxylation of 5-amino-orotic acid

and a Schiff base derivative by rhenium(V) Inorg Chem Comm 57 (2015) 54-

57

[23] K Potgieter P Mayer T Gerber N Yumata E Hosten I Booysen R Betz M

Ismail B van Brecht Rhenium(I) tricarbonyl complexes with multidentate

nitrogen-donor derivatives Polyhedron 49 (2013) 67-73

[24] IN Booysen I Ebinumoliseh MP Akerman B Xulu A rhenium(I) compound

bearing a dimerized chromone NO bidentate chelator Inorg Chem Comm 62

(2015) 8-10

[25] P Mayer TIA Gerber B Buyambo A Abrahams Coordination behaviour of

acetylacetone-derived Schiff bases towards rhenium(I) and (V) Polyhedron 28

(2009) 1174-1178

[26] T Jurca O Ramadan I Korobkov DS Richeson Employing sterically

encumbered bis(imino)pyridine ligands in support of fac-rhenium(I) carbonyls

J Organomet Chem 802 (2016) 27-31

[27] J Ho WY Lee KJT Koh PPF Lee YK Yan Rhenium(I) tricarbonyl

complexes of salicylaldehyde semicarbazones Synthesis crystal structures and

cytotoxicity J Inorg Biochem 119 (2013) 10-20

[28] B Machura A Świtlicka M Wolff J Kusz R Kruszynski Mono- and di-

nuclear oxorhenium(V) complexes of 47-diphenyl-110-phenanthroline

Polyhedron 28 (2009) 3999-4009

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

[29] B Machura M Jaworska P Lodowski Natural bond orbital analysis and

density functional study of linear and bent oxo-bridged dimers of rhenium(V)

J Mol Struc-Theochem 766 (2006) 1-8

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

Highlights

bull Chromone rhenium(I) compounds

bull Simulated IR spectra

bull Low calculated RMSDs

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

References

[1] JR Dilworth SJ Parrott The biomedical chemistry of technetium and

rhenium Chem Soc Rev 27 (1998) 43-55

[2] S Jurisson D Berning J Wei M Dangshe Coordination compounds in

nuclear medicine Chem Rev 93 (1993) 1137-1156

[3] S Juumlrgens WA Herrmann FE Kuumlhn Rhenium and technetium based

radiopharmaceuticals Development and recent advances J Organomet Chem

751 (2014) 83-89

[4] U Abram R Alberto Technetium and Rhenium - Coordination Chemistry and

Nuclear Medical Applications Braz Chem Soc 17 (2006) 1486-1500

[5] SL Binkley TC Leeper RS Rowlett RS Herrick CJ Ziegler

Re(CO)3(H2O)3+ binding to lysozyme structure and reactivity Mettalomics 3

(2011) 909-916

[6] RS Herrick TJ Brunker C Maus K Crandall A Cetin CJ

Ziegler Aqueous preparation and physiological stability studies of

Re(CO)3(tripodal) compounds Chem Commun (2006) 4330-4331

[7] K Potgieter P Mayer TIA Gerber IN Booysen Coordination behaviour of

the multidentate Schiff base 26-bis(2-hydroxyphenyliminomethyl)pyridine

towards the fac-[Re(CO)3]+ and [ReO]3+ cores Polyhedron 28 (2009) 2808-2812

[8] CL Ferreira CB Ewart SR Bayly B O Patrick J Steele MJ Adam C

Orvig Glucosamine Conjugates of Tricarbonylcyclopentadienyl Rhenium(I)

and Technetium(I) Cores Inorg Chem 45 (2006) 6979-6987

[9] Q Nadeem D Can Y Shen M Felber Z Mahmooda R Alberto Synthesis of

tripeptide derivatized cyclopentadienyl complexes of technetium and rhenium

as radiopharmaceutical probes Org Biomol Chem 12 (2014) 1966-1974

[10] IN Booysen M Ismail TIA Gerber M Akerman B Van Brecht Oxo and

oxofree rhenium(V) complexes with NO-donor Schiff bases S Afr J Chem 65

(2012) 174-177

[11] IN Booysen MB Ismail OQ Munro Mono- and dinuclear rhenium(I)

compounds with bidentate benzimidazole chelators Inorg Chem Commun 30

(2013) 168-172

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

[12] IN Booysen MB Ismail MP Akerman Coordination behaviour of chromone

Schiff bases towards the [ReVO]3+ and [ReI(CO)3]+ cores J Coord Chem 66

(2013) 4371-4386

[13] S Bhatnagar S Sahir P Kackar S Kaushik MK Dave A Shukla A Goel

Synthesis and docking studies on styryl chromones exhibiting cytotoxicity in

human breast cancer cell line Bioorg Med Chem Lett 20 (2010) 4945-4950

[14] M Recanatini A Bisi A Cavalli F Belluti S Gobbi A Rampa P Valenti M

Palzer A Palusczak RW Hartmann A New Class of Nonsteroidal Aromatase

Inhibitorsthinsp Design and Synthesis of Chromone and Xanthone Derivatives and

Inhibition of the P450 Enzymes Aromatase and 17α-HydroxylaseC1720-

Lyase J Med Chem 44 (2001) 672-680

[15] IN Booysen A Adebisi MP Akerman OQ Munro B Xulu Coordination of

di- and triimine ligands at ruthenium(II) and ruthenium(III) centers structural

electrochemical and radical scavenging studies J Coord Chem (2016) doi

1010800095897220161177177

[16] Bruker APEX2 SAINT and SADABS Bruker AXS Inc (2010) Madison

Wisconsin USA

[17] RH Blessing An empirical correction for absorption anisotropy Acta Cryst

A51 (1995) 33-38

[18] GM Sheldrick A short history of SHELX Acta Cryst A64 (2008) 112-122

[19] LJ Farrugia WinGX and ORTEP for Windows an update J Appl Cryst 45

(2012) 849-854

[20] MJ Frisch GW Trucks HB Schlegel GE Scuseria MA Robb JR

Cheeseman G Scalmani V Barone B Mennucci GA Petersson H Nakatsuji

M Caricato X Li HP Hratchian AF Izmaylov J Bloino G Zheng JL

Sonnenberg M Hada M Ehara K Toyota R Fukuda J Hasegawa M Ishida

T Nakajima Y Honda O Kitao H Nakai T Vreven JA Montgomery Jr JE

Peralta F Ogliaro M Bearpark JJ Heyd E Brothers KN Kudin VN

Staroverov R Kobayashi J Normand K Raghavachari A Rendell JC

Burant SS Iyengar J Tomasi M Cossi N Rega JM Millam M Klene JE

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

Knox JB Cross V Bakken C Adamo J Jaramillo R Gomperts RE

Stratmann O Yazyev AJ Austin R Cammi C Pomelli JW Ochterski RL

Martin K Morokuma VG Zakrzewski GA Voth P Salvador JJ

Dannenberg S Dapprich AD Daniels O Farkas JB Foresman JV Ortiz J

Cioslowski DJ Fox GAUSSIAN 09 (Revision A01) Gaussian

IncWallingford CT (2009)

[21] A Brink HG Visser A Roodt Novel imino rhenium(I) tricarbonyl complexes

of salicylidene-derived ligands Synthesis X-ray crystallographic studies

spectroscopic characterization and DFT calculations Polyhedron 52 (2013) 416-

423

[22] J Mukiza TIA Gerber EC Hosten Decarboxylation of 5-amino-orotic acid

and a Schiff base derivative by rhenium(V) Inorg Chem Comm 57 (2015) 54-

57

[23] K Potgieter P Mayer T Gerber N Yumata E Hosten I Booysen R Betz M

Ismail B van Brecht Rhenium(I) tricarbonyl complexes with multidentate

nitrogen-donor derivatives Polyhedron 49 (2013) 67-73

[24] IN Booysen I Ebinumoliseh MP Akerman B Xulu A rhenium(I) compound

bearing a dimerized chromone NO bidentate chelator Inorg Chem Comm 62

(2015) 8-10

[25] P Mayer TIA Gerber B Buyambo A Abrahams Coordination behaviour of

acetylacetone-derived Schiff bases towards rhenium(I) and (V) Polyhedron 28

(2009) 1174-1178

[26] T Jurca O Ramadan I Korobkov DS Richeson Employing sterically

encumbered bis(imino)pyridine ligands in support of fac-rhenium(I) carbonyls

J Organomet Chem 802 (2016) 27-31

[27] J Ho WY Lee KJT Koh PPF Lee YK Yan Rhenium(I) tricarbonyl

complexes of salicylaldehyde semicarbazones Synthesis crystal structures and

cytotoxicity J Inorg Biochem 119 (2013) 10-20

[28] B Machura A Świtlicka M Wolff J Kusz R Kruszynski Mono- and di-

nuclear oxorhenium(V) complexes of 47-diphenyl-110-phenanthroline

Polyhedron 28 (2009) 3999-4009

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

[29] B Machura M Jaworska P Lodowski Natural bond orbital analysis and

density functional study of linear and bent oxo-bridged dimers of rhenium(V)

J Mol Struc-Theochem 766 (2006) 1-8

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

Highlights

bull Chromone rhenium(I) compounds

bull Simulated IR spectra

bull Low calculated RMSDs

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

[12] IN Booysen MB Ismail MP Akerman Coordination behaviour of chromone

Schiff bases towards the [ReVO]3+ and [ReI(CO)3]+ cores J Coord Chem 66

(2013) 4371-4386

[13] S Bhatnagar S Sahir P Kackar S Kaushik MK Dave A Shukla A Goel

Synthesis and docking studies on styryl chromones exhibiting cytotoxicity in

human breast cancer cell line Bioorg Med Chem Lett 20 (2010) 4945-4950

[14] M Recanatini A Bisi A Cavalli F Belluti S Gobbi A Rampa P Valenti M

Palzer A Palusczak RW Hartmann A New Class of Nonsteroidal Aromatase

Inhibitorsthinsp Design and Synthesis of Chromone and Xanthone Derivatives and

Inhibition of the P450 Enzymes Aromatase and 17α-HydroxylaseC1720-

Lyase J Med Chem 44 (2001) 672-680

[15] IN Booysen A Adebisi MP Akerman OQ Munro B Xulu Coordination of

di- and triimine ligands at ruthenium(II) and ruthenium(III) centers structural

electrochemical and radical scavenging studies J Coord Chem (2016) doi

1010800095897220161177177

[16] Bruker APEX2 SAINT and SADABS Bruker AXS Inc (2010) Madison

Wisconsin USA

[17] RH Blessing An empirical correction for absorption anisotropy Acta Cryst

A51 (1995) 33-38

[18] GM Sheldrick A short history of SHELX Acta Cryst A64 (2008) 112-122

[19] LJ Farrugia WinGX and ORTEP for Windows an update J Appl Cryst 45

(2012) 849-854

[20] MJ Frisch GW Trucks HB Schlegel GE Scuseria MA Robb JR

Cheeseman G Scalmani V Barone B Mennucci GA Petersson H Nakatsuji

M Caricato X Li HP Hratchian AF Izmaylov J Bloino G Zheng JL

Sonnenberg M Hada M Ehara K Toyota R Fukuda J Hasegawa M Ishida

T Nakajima Y Honda O Kitao H Nakai T Vreven JA Montgomery Jr JE

Peralta F Ogliaro M Bearpark JJ Heyd E Brothers KN Kudin VN

Staroverov R Kobayashi J Normand K Raghavachari A Rendell JC

Burant SS Iyengar J Tomasi M Cossi N Rega JM Millam M Klene JE

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

Knox JB Cross V Bakken C Adamo J Jaramillo R Gomperts RE

Stratmann O Yazyev AJ Austin R Cammi C Pomelli JW Ochterski RL

Martin K Morokuma VG Zakrzewski GA Voth P Salvador JJ

Dannenberg S Dapprich AD Daniels O Farkas JB Foresman JV Ortiz J

Cioslowski DJ Fox GAUSSIAN 09 (Revision A01) Gaussian

IncWallingford CT (2009)

[21] A Brink HG Visser A Roodt Novel imino rhenium(I) tricarbonyl complexes

of salicylidene-derived ligands Synthesis X-ray crystallographic studies

spectroscopic characterization and DFT calculations Polyhedron 52 (2013) 416-

423

[22] J Mukiza TIA Gerber EC Hosten Decarboxylation of 5-amino-orotic acid

and a Schiff base derivative by rhenium(V) Inorg Chem Comm 57 (2015) 54-

57

[23] K Potgieter P Mayer T Gerber N Yumata E Hosten I Booysen R Betz M

Ismail B van Brecht Rhenium(I) tricarbonyl complexes with multidentate

nitrogen-donor derivatives Polyhedron 49 (2013) 67-73

[24] IN Booysen I Ebinumoliseh MP Akerman B Xulu A rhenium(I) compound

bearing a dimerized chromone NO bidentate chelator Inorg Chem Comm 62

(2015) 8-10

[25] P Mayer TIA Gerber B Buyambo A Abrahams Coordination behaviour of

acetylacetone-derived Schiff bases towards rhenium(I) and (V) Polyhedron 28

(2009) 1174-1178

[26] T Jurca O Ramadan I Korobkov DS Richeson Employing sterically

encumbered bis(imino)pyridine ligands in support of fac-rhenium(I) carbonyls

J Organomet Chem 802 (2016) 27-31

[27] J Ho WY Lee KJT Koh PPF Lee YK Yan Rhenium(I) tricarbonyl

complexes of salicylaldehyde semicarbazones Synthesis crystal structures and

cytotoxicity J Inorg Biochem 119 (2013) 10-20

[28] B Machura A Świtlicka M Wolff J Kusz R Kruszynski Mono- and di-

nuclear oxorhenium(V) complexes of 47-diphenyl-110-phenanthroline

Polyhedron 28 (2009) 3999-4009

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

[29] B Machura M Jaworska P Lodowski Natural bond orbital analysis and

density functional study of linear and bent oxo-bridged dimers of rhenium(V)

J Mol Struc-Theochem 766 (2006) 1-8

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

Highlights

bull Chromone rhenium(I) compounds

bull Simulated IR spectra

bull Low calculated RMSDs

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

Knox JB Cross V Bakken C Adamo J Jaramillo R Gomperts RE

Stratmann O Yazyev AJ Austin R Cammi C Pomelli JW Ochterski RL

Martin K Morokuma VG Zakrzewski GA Voth P Salvador JJ

Dannenberg S Dapprich AD Daniels O Farkas JB Foresman JV Ortiz J

Cioslowski DJ Fox GAUSSIAN 09 (Revision A01) Gaussian

IncWallingford CT (2009)

[21] A Brink HG Visser A Roodt Novel imino rhenium(I) tricarbonyl complexes

of salicylidene-derived ligands Synthesis X-ray crystallographic studies

spectroscopic characterization and DFT calculations Polyhedron 52 (2013) 416-

423

[22] J Mukiza TIA Gerber EC Hosten Decarboxylation of 5-amino-orotic acid

and a Schiff base derivative by rhenium(V) Inorg Chem Comm 57 (2015) 54-

57

[23] K Potgieter P Mayer T Gerber N Yumata E Hosten I Booysen R Betz M

Ismail B van Brecht Rhenium(I) tricarbonyl complexes with multidentate

nitrogen-donor derivatives Polyhedron 49 (2013) 67-73

[24] IN Booysen I Ebinumoliseh MP Akerman B Xulu A rhenium(I) compound

bearing a dimerized chromone NO bidentate chelator Inorg Chem Comm 62

(2015) 8-10

[25] P Mayer TIA Gerber B Buyambo A Abrahams Coordination behaviour of

acetylacetone-derived Schiff bases towards rhenium(I) and (V) Polyhedron 28

(2009) 1174-1178

[26] T Jurca O Ramadan I Korobkov DS Richeson Employing sterically

encumbered bis(imino)pyridine ligands in support of fac-rhenium(I) carbonyls

J Organomet Chem 802 (2016) 27-31

[27] J Ho WY Lee KJT Koh PPF Lee YK Yan Rhenium(I) tricarbonyl

complexes of salicylaldehyde semicarbazones Synthesis crystal structures and

cytotoxicity J Inorg Biochem 119 (2013) 10-20

[28] B Machura A Świtlicka M Wolff J Kusz R Kruszynski Mono- and di-

nuclear oxorhenium(V) complexes of 47-diphenyl-110-phenanthroline

Polyhedron 28 (2009) 3999-4009

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

[29] B Machura M Jaworska P Lodowski Natural bond orbital analysis and

density functional study of linear and bent oxo-bridged dimers of rhenium(V)

J Mol Struc-Theochem 766 (2006) 1-8

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

Highlights

bull Chromone rhenium(I) compounds

bull Simulated IR spectra

bull Low calculated RMSDs

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

[29] B Machura M Jaworska P Lodowski Natural bond orbital analysis and

density functional study of linear and bent oxo-bridged dimers of rhenium(V)

J Mol Struc-Theochem 766 (2006) 1-8

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

Highlights

bull Chromone rhenium(I) compounds

bull Simulated IR spectra

bull Low calculated RMSDs

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

Highlights

bull Chromone rhenium(I) compounds

bull Simulated IR spectra

bull Low calculated RMSDs