Indi an Journal of Chemistry Vol. 40A, July 2001, pp. 775-779

Synthesis and spectral studies on chromium(III), manganese(II), iron(III),

cobalt(II), nickel(II) and copper(II) complexes of fourteen-membered and

sixteen membered tetradentate macrocyclic ligands

Sulekh Chandra* & Karuna Gupta Department of Chemistry , Zakir Husain College (U niversi ty of

Delhi), J L Nehru Marg, New Delhi 110002, Indi a

Received 12 December 2000; revised 9 April 2001

Complexes of Cr(III), Mn(II), Fe(lll), Co(ll), Ni(lI) and Cu(ll) with a 14- and 16- membered macrocyclic ligands have been pre­pared and characterized by elemental analyses, molar conduc­tance, magnetic moment, infrared , electronic and EPR spectral studies. All the complexes are found to have six-coordinate ge­ometry and are of the high-spin type.

Early observations on complexes with substituted 14-membered tetraaza macrocyclic ligands led to the suggestion that a constrictive effect might be respon­sible for their surprisingly large ligand field strengths l

. Also steric advantages of symmetrical 14-membered macrocycle leads to stabilize unusal oxi­dation state2. Although Cu(II), Ni(II) and Cr(lll ) complexes of macrocyclic ligand prepared by the condensation of triethyleneteramine and acetylacetone has already been reported2-3, we report here the syn­thesis and characterization of 14- and 16- membered macrocycle by the [2+2] condensation of ~-diketone (acetylacetone) and o-phenylenediamine/ m­phenylenediamine. The Cr(lll), Mn(II), Fe(III), Co(lI) , Ni(II) and Cu(II) complexes of the macrocy­clic ligand Dibenzo-[b,i] -8, 10, 19,21-tetramethyl­[1,5,8,12]-tetraazacyclotetradeca-l, 3, 5, 7, 10, 12, 14, 16,18,21-decene(Lt. a 14-membered ligand) ,and 1,5: II , 15-dimetheno-2, 4, 10, 12-tetramethyl-[ I, 5, 9,13]­tetraazacyclohexadeca-I , 3, 5, 6, 10, II, 13, 15,16,20-decene(L2' a 16-membered ligand) were synthesized and characterized.

Experimental Preparation of ligand

To an ethanolic solution (30 mL) of acetylacetone (5 mL, 0.05 mol), ethanolic solution of 0-

phenylenediamine/m-phenylenediamine (0.05 mol) was added in presence of few drops of conc.HC\. The resultant solution was refluxed for one week and then after concenterating, solution was kept for several days, but formation of macrocyclic ligand does not take place so complexes are prepared by tempelate procedure.

Preparation of complexes A template reaction was carried out for the forma­

tion of the complexes. A hot ethanolic solution (20 mL) of the metal salt (0.025 mol) was mixed with a hot ethanolic solution (20 mL) of o-phenylenediamine/ m-phenylenediamine (0.05 mol) for LI and L2 ligands respectively. Then an ethanolic solution (20 mL) of acetylacetone (5 mL, 0.05 moL) in the presence of a few drops of conc. HCI was added to the resultant solution .The solution was refluxed for about 4-5 h in each case. The complexes precipitated out on cooling the reaction mixture overnight. The complexes were filtered, washed with ethanol and dried over P4 0 10•

Microanalysis(C, Hand N) of these complexes were carried out on a Carlo-Erba 1106 elemental analyzer. The elemental analysis data are reported in Table 1. IR spectra were recorded on a Perkin Elmer 137 instrument as nujol mulls/KBr pellets. Electronic spectra were recorded in DMF solution on a Shima­dzu UV mini -1240 spectrophotometer. Molar Con­ductance was measured on an ELiCO conductivity Bridge (Type C M 82 T). Magnetic susceptibility measurements (Gouy Balance) were made at room temperature using CuS04.5H20 as cali brant. EPR spectra of the complexes were recorded as powder samples at room temperature on an E-4-EPR spec­trometer using DPPH as the g-marker.

Results and discussion All the complexes were found to have the compo­

sitions MLCI2 (where M= Mn2+, C02

+, Ni2+ and Cu2+)

or MLCI3 (where M'= Cr3+ and Fe3+), also in both cases L can be either LI and L2. Molar conductance measurements of these complexes in DMF corre­sponded to nonelectrolytes and 1: I electrolytes re­spectively. Therefore, these complexes may be for­mulated as [MLCh] and [M'LCh]C\. The IR spectra show the absence of absorption -3400 cm-I. This

776 INDIAN J CHEM, SEC. A, JULY 2001

Table I--Characterization data of the complexes

Complexes Mol.wt. % Yield M.pt Colour Found (ealed), % Molecular Found (Caled.) (0C)

Formula M C H N

[CrL ICl2lCI 503 68 232 Black 10.34 52.53 4.77 1l.l4

CrCn N4H24C1J (502.4) (9 .98) (52.04) (4 .0 1) (10.98)

[MnL ICl21 469 (468.9) 68 235 Brown 11 .69 56.17 5. 10 11.91 MnCn N4H24CI2 (1 1.86) (55.67) (4.9 1) (10.79)

[FeL ICl21CI 504 (504.34) 55 235 Black 11 .02 52.14 4.74 11 .06 MnCn N4H24C1J (I 1.89) (52.15) (4. 30) ( 11.03)

[CoL ICl21 473 (472.93) 63 243 Brown 12.43 55.70 5.06 11.8 1 CoC22 N4H24C12 ( 11.98) (54.76) (4.93) (11.01 )

[NiL ICl21 472 (472.69) 59 238 Dark brown 12.39 55.73 5.07 11.82

NiC22N4H 24C1 2 ( 12.65) (54 .91 ) (4 .72) (10.86)

[CuLICl21 478 65 240 Black 13.28 55.17 5.02 11.70

CUC22 N4H24C12 (477.54) (12.78) (55.74) (4.77) ( 10.98)

[CrL2C121Cl 501 65 235 Dark brown 10.34 52.53 4.77 1l.l4

CrCnN4H24C1J (502.4) (10.41) (52.30) (4 .06) (11.01)

[MnL2C1 21 469 62 238 Dark brown 11.69 56.17 9.10 11.91 MnCn N4H24C1 2 (468.9) ( 10.98) (56.78) (9.9 1 ) (11.01 )

iFeL2C12lCI 505 60 239 Black 11 .02 52.14 4.74 11 .06 FeCn N4H24C1J (504.34) (10.39) (51 .82) (4.67) (10.93)

[CoL2C121 474 72 235 Green 12.43 55.77 5.06 11.81

COCn N4H24C1 2 (472.93) ( 12.88) (55 .07) (5.9 1 ) ( 10.91 )

[NiL2C121 472 64 240 Black 12.39 55.73 5.07 11.82

NiC22 N4H24C12 (472.69) ( 12.58) (55.02) (4.93) (10. 15)

[CuL2C12] 477 65 238 Dark brown 13.28 55 .17 5.02 11.70 CUCn N4H 24C12 (477.54) ( 13.91) (54.80) (4 .73) (11.04)

L 1= Dibenzo-[b.i1-8,1 O,19,21-tetramethyl-[ 1,5,8,121-tetraazacyclotetradeca-I,3,5,7,IO,12,14,16,18,21-decene. L2 = 1,5: 1I , 15-dimetheno-2,4, IO,12-tetramethy l-[ 1,5,9, 13l-tetraazacyclohexadeca- 1 ,3,5 ,6, I 0, 11 ,13,1 5, 16,20-decene

Table 2-Electronic spectral bands (cm,I), Ema. ( M,I cm, l ) and magnetic moments

Complexes VI (Ema.) V2 (Em,.) VJ (Ema.) V4 (Em,.) Ilcff

(B.M.) [CrL ICI21CI 18,500 (57) 22,650 (6 1) 25,100 (64) 29,100 (125) 3.76

[MnL I C12] 18,200 (78) 24,800 ( 11 3) 29,700 (210) 31,900 (920) 5.95

[FeL ICl2)CI 16,800 (115) 20,500 (193) 25,900 (310) 5.95

ICoL I CI21 8,700 (25) 14,000 (35) 20,500 (390) 5.05

[NiLI CI21 10,800 (7) 16,700 (17) 15,000 (35) 3.00

[CuL ICl 21 13,700 (48) 18,600 (125) 34,200 (784) 1.90

[CrL2C12]CI 18,500 (53) 22,500 (58) 25 , 100 (65) 28,900 (1 18) 3.82

[MnL2C121 18,000 (67) 24,750 ( 123) 29,500 (320) 31,900 (835) 6.01

[FeL2C12]CI 16,900 (112) 19,900 ( 173) 25,600 (323) 5.93

[CaL2 CI 21 8,850 (28) 14, 100 (49) 20,650 (298) 4.99

[NiL2 Cl2l 10,500 (9) 16,550 ( 17) 24,900 (46) 3.02

[CuL2 Cil l 13,500 (52) 18,500 (1 23) 2.00

'Solvent used is DMF

NOTES 777

Table J--Ligand field parameters

Complexes Dq(em·l) B(em·l

)

[CrL ICI21CI 1,850 373 [MnL lCi21 1,820 700 [FeL ICI 2JCi [CoL lCi 21 1,018 1,061 [NiL ICI21 1,080 600 [CuL lCi21 [CrL2Ci21CI 1,850 358 [MnL2Ci21 1,800 679 [FeL2Ci21CI [CoL2CI 21 1,036 1,079 [NiL2Ci21 1,050 663 [CuL2C1 21

shows the absence of free amino groups. The charac­teristic bands due to chelated ligands appear in the range 1500-1700 cm·1 . The VC=N4 band (1620 cm· l

)

shifted to lower side in the complexes suggesting the coordination through the nitrogen of VC=N group.

The electronic spectra of the chromium(III) com­plexes recorded in DMF display four bands in the range 18500-29200 cm·1 (Table 2). Six-coordinate complexes with Olr symmetry show three spin­allowed bands5 of which the highest energy band as­signable to the 4A I g~ 4A2g transition, occurs above 30,000 cm· l

. The spectrum of the complex under study shows four bands below 30,000 cm· l

, which cannot be interpreted in terms of idealized symmetry elements in the complexes. Such six-coordinated chromium(III) complexes can have either effective C4v or D41r symmetry. In the present complex, the four transItIOns observed may be assigned to 4Blg~4Eg"(VI)' 4Blg~4B2g (V2) , 4Bl g~4E/(V3) and 4Blg~4Alg(V4) transitions arising from the lifting of the degeneracy of the orbital triplet (in octahedral symmetry) in the order of increasing energy and as­suming effective D41r symmetry around the metal ion. In Olr symmetry, VI and V2 are derived from the 4T2g level, whilst V3 and V4 from 4TI g (F). The C4v symme­try has been ruled out because of the higher splitting of the first band.

Various ligand field parameters have been evalu­ated and given in (Table 3). The nephelauxetic pa­rameter,~ is readily obtained using the relation ~ = B (complex)1B (free ion) and the complex has apprecia­ble covalent character. The spectral data of Cr(Me4[14]tetraene)(H20)z3+ reported in ref.2 is found to be comparable with what we have reported as they have reported Amax at 545 nm and shoulder at 450 nm,

13 LFSE(KJ/mol)

OAO 265.6 0.89

0.94 218.9 0.58 153A

0.39 265.6 0.86

0.96 222.8 0.64 150.5

Slight changes observed in our case is might be due to rigidity of amine used. The EPR spectra of the com­plexes have been recorded as polycrystalline samples at room temperature. The g-value is calculated using the expression g =2.0023 (l-4A11O Dq) where A is the spin orbit coupling constant for the metal ion in the complex. The g-values are found to be 1.97 and 1.95 respectively for the complex of ligand LI and L2.The electronic spectrum of the manganese(II) complexes display weak absorption bands in region 17,700-31,700 cm· l

, characteristic of octahedral geometrl. These bands may be assigned to 6Al g~4Tlg (4C) (V I), 6Alg~4Eg (4C) (V2), 6Al g~4Eg (4D) (V3) and 6Alg~4Tlg (4p) (V4) transitions respectively. The values for the ligand field parameters have been calculated and given in Table 3. The value of Dq could be evaluated with the help of transition energies vs Dq by Orgd using the energy due to the transition 6A1 8~4T18 (4C).

The calculated value of ~ indicates that the complexes under study have covalent character.

The EPR spectra of the complexes have been re­corded as polycrystalline sample. The polycrystalline samples gives one broad isotropic signal centered ap­proximately at l.98 and l.89 for the ligand LI and L2 and the free electron g-value (go = 2.0023). The broadening of the spectra is due to spin relaxation8

. In DMF solution, the complex gives an EPR spectrum containing six lines arising due to hyperfine interac­tion9

.11 between the unpaired electrons with the 55Mn

nucleus (1= 512). The nuclear magnetic quantum numbers, MI, corresponding to the lines are -512, -3/2, -1/2, +112, +3/2, +512 from low to high field. Iron(III) complexes show magnetic moment corre­sponding to five unpaired electrons (Table 2) indicate the presence of the high-spin Fe(III) ion. The high-

778 INDIAN J CHEM, SEC. A, JULY 200 I

spin Fe(llI) state is also confirmed by Mossbauer pa­rameters. The observed isomer shift values are 0.6323 mmsec· 1 and 0.6716mmsec·1 for LI and L2 respec­tively, at 300K which indicates that iron exist in +3 oxidation state" with S=5/2. Quadrupole splitting values are 1.1305mmsec" and 1.0640 mmsec·1 for LI and L2 respectively for high-spin Fe(IJI) complexes. In iron (III) complexes, there is no valence contribu­tion to the QS The only source of QS therefore re­mains the lattice contribution arising mainly from the asymmetry of the ligand field, which is further sup­ported by the temperature independence of QS value. The electronic spectra of these complexes show three bands in range 16,800-25,900 cm·1 which are charac­teristic of octahedral geometry. The electronic spectra of cobalt(II) exhibit a broad band and two shoulders in range 8800-20,600 cm·1 .These bands may be as-. 4 4 4 4 ) d 4T 4T Signed to T Ig-,; T 2g (VI), T Ig-,; A 2g (V2 an Ig-'; Ig

(V3), respectively. The lower values of V2 IVI (1.609 for LI and for L2 1.593) may be due to distortion of the octahedral structure I2.13. This is consistent with the very broad nature of the VI bands, which may be best assigned to the envelope of the transitions from 4E / TI g) to the components 4B2g and 4E g of 4T2g, char­acteristic of a tetragonally distorted octahedral en­viomment I3

.

EPR spectra of complexes under study were re­corded at liquid nitrogen temperature. Because the rapid spin lattice relaxation of C02

+ broadened the lines at higher temperature. The observed g-values for LI are as follows: gIl == 5.354 g1. = 2.617 and for L2 are as follows gIl = 5.092 g1. = 2.909.The large devia­tion of the g-values from the spin only value (go = 2.0023) is due to the large angular momentum contri­bution. The electronic spectra of the nickel(II) com­plexes show two well-defined bands in the region 10500-16700 cm·1 assignable to 3A 2g-,;3T2g (VI) and 3A2g-,;3T' g (F,V2) transitions respectively, in an octa­hedral structure. The third dod transition bands (V3), which may be obscured by the more intense charge transfer band, is calculated theoretically and found to be in range 24900-25000 cm· l. The value of V2 IVI is found to be 1.55 for LI and 1.57 for L2. The ligand

A I ~ field parameters Dq, B and I-' have been calculated -and reported in Table 3. The magnetic moment values are reported in (Table 2) corresponding to two un­paired electrons are characteristic of an octahedral geometry.

The magnetic moment of the copper(II) complexes at room temperature corresponds to one unpaired

electron and reported in Table 2. The complexes may be considered to have tetragonal geometry. The elec­tronic spectrum of six-coordinated Cu(II) complexes have either D4h or C4v symmetry, and the E g and T 2g

levels of the 2D free ion will split into Bi g, A Ig, B 2g and E g levels respectively. Thus three spin-allowed transi­tions are expected, in the visible and near-IR region . Only few complexes are known '3 in which such bands are resolved either by "Gaussian analysis" or by "Sin­gle Crystal Polarization" studies. These bands have been assigned to the following transitions in order of .. 2B 2A (d 2 ~ d 2 ) 2B II1creasll1g energy. Ig -'; Ig x·y - ~ z , V I , Ig

2 2 ~ ~ 2 22 -'; B 2g(dx .y- ~ dxy, V3) and - Big -'; E g (dx .y ~ dx:.yz ,

V3). The energy level sequence will depend on the amount of tetragonal distortion due to ligand-field and lahn-Teller distortion l4 . The electronic spectra of the complexes reported here show two characteri stic bands in range 13,500-18,600 cm·1 and a charge trans­fer bands - at 34400 cm·l. The 2BI -'; 2B 28 (V3) transi­tion is usually not observed as a separate band in the tetragonal field. The complex shows anisotropic ESR spectrum characteristic of tetragonal Cu(IJ). Observed g-values for ligand Llare as follows gIl =2 .2615, g1. = 2.0555, go' = 2.124 and G = 4.75, while for L2 gIl =2.2714, g1. = 2.0610, go' = 2.131 and G = 4.75. The anisotropic g values have been calculated by Kneubuhl's methods 15 and methods reported earlier ' 6.

G = (gw2)/(g1.-2) which measures the exchange inter­action between copper centers in a polycrystalline solid has been calculated. According to Hathaway l6.19 if the G value is greater than 4, the exchange interac­tion is negligible, while a value of G less than 4 indi­cates a considerable exchange in the solid complexes. As G = 2.77 for the present complex, indicates that there is some exchange interaction in the complex.

On the basis of above analysis, the following struc­ture (Figs 1 and 2) may be suggested for the complex .

y' B,,\ ), /H,

CX~D II : «

/c"j/" B,C ~ CH,

':'> (;,

Siructurt: of Ole c:om~exes of L] where M - Mnen). Co(D). N;(IQ and Cu( IQ

StruclUrc or the complexCl of LJ whcr-e M' - C~UI) and Fe(IIQ

Fig. l---Structure of the complexes with ligand L,

NOTES 779

yl

H,C" /~H' /CH, c : "c

b Structure of the complex with ~ and where M- Mn(Il). Co(ll). Ni(Il) and Cu(ll)

yl

H,C, /~H' /CH, 'c : "c

b Structure of the complu with L:2 and where M'zCr(Dl) and Fe(Ill)

Fig. 2- Structure of the complexes with L2

Acknowledgement

CI

The authors are thankful to the DST, New Delhi , UGC, Delhi for financial assistance and lIT Mumbai , for recording EPR spectra.

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