Indian Journal of ChemistryVol.34A, January 1995, pp. 72-75

Synthesis and characterization of5, 12-dioxa-7 ,14-dimethyl-l ,4,8, ll-tetra-azacyc1otetradeca-l ,8-diene and its metal

complexes with chromium(II),manganese(II), iron(II), copper(II),nickel(II) and zinc(II) metal ions

Mohammad Shakir", Saji P Varkey & Tahir A KhanDivision of Inorganic Chemistry, Department of Chemistry

Aligarh Muslim University, Aligarh 202002

Received 19 April 1994; revised 15 June 1994;accepted 1 August 1994

The macrocyc!ic ligand 5,12-dioxa-7,14-dimethyl-1,4,8,1l-tetraazacyc!otetradeca-l ,8-diene, (~ or 1-;)has been prepared by the condensation reaction of1,2-diaminoethane with alkylacetoacetate in methanolmedium at room temperature. A few metal complexesof Cr(I1), Mn(II), Fe(II), Cu(II), Ni(II) and Zn(II) withthese macrocyc1ic ligand (L, or 1-;) have been synthes-ized and characterized by elemental analysis, magneticsusceptibility measurements, IR, IH NMR, mass, EPRand electronic spectral studies. An octahedral geome-try is suggested for the complexes [M~ e12] or[ML102] when M =Cr(II), Mn(II), Fe(II), Cu(II), Zn(II)and a square planar geometry is proposed in the caseof Ni(I1) complex.

The chemistry of tetraazamacrocyclic ligands hasbeen of growing interest to coordination chemists,followed by the earlier work on the metal con-trolled template synthesis of macrocyclicspecies I- 5. A large number of workers" - 8 are cur-rently engaged in the synthesis of polyamide mac-rocycles and their coordination chemistry which isof particular interest in view of two potential don-or atoms, i.e. amide nitrogen and amide oxygen.However, in most of the polyamide macrocycliccomplexes, amide nitrogen is engaged in coordi-nation and not the oxygen-":". Recently we re-ported":" - 13 the template synthesis of polyamideand mixed donor macrocyclic complexes. In thisnote we report the synthesis and characterizationof diamidediimine macro cycles L, or r...;, obtainedfrom the condensation of 1,2-diaminoethane withalkylacetoacetate and their coordinating behaviourwith first row transition metal ions.

ExperimentalThe chemicals, methyl acetoacetate, ethylacetoa-

cetate and 1,2-diaminoethane (all E. Merck) were

used without further purification. The metal saltsused were of BDH quality. All the solvents weredried before use.

Synthesis of5, 12-dioxa- 7, 14-dimethyl-1,4,8,1l-tetraazacyclotetradeca-l ,8-diene (L. orL;)

To a magnetically stirred solution of 1,2-diami-no ethane (0.02 mol) in methanol t: 50 cm ') wasadded a solution of methylacetoacetate (L.) orethylacetoacetate (0.02 mol) (L;) in methanol(- 50 em:'), The resulting mixture was stirred for- 2 h. The contents were then kept at room tem-perature for 12 h which resulted in the formationof fine shining colourless crystalline compounds.They were washed with methanol and dried invacuo. The purity of these compounds waschecked by TLC.

Synthesis of dichloro (5, 12-dioxa-7, 14-dimethyl-1,4,8, ll-tetraazacyclotetradeca-1 ,8-diene)meta~lI), [ML. C~] or[M~ P2] [M= ccu ;Mn(II), Fe../I), O~/I) andZn{II);

The ligand L. or r...;, (Q.01 mol) dissolved indichloromethane ( - 50 ern") was added dropwiseto a magnetically stirred methanolic solution (-50 crn') of metal salts (0.01 mol). The resultingmixture was then stirred for additional 4 h atroom temperature which resulted in the formationof a crystalline solid product. The product formedwas filtered and dried in vacuo.

Synthesis of(5,12-dioxa-7, 14-dimethyl-1,4,8, 11-tetraazacyclotetradeca-l,8-diene) nickel (II) chlo-ride, [NiL.]Cl2 or[NiL;]CI2

The nickel complexes were also synthesized bythe method described above.

The elemental analyses were obtained fromMicro-analytical Laboratory, CDRl, Lucknow.The IH NMR spectra in DMSO-d6 using BrukerAC 200E nuclear magnetic resonance spectrome-ter with Me4Si as an internal standard was ob-tained from GNDU, Amritsar. The metals andchlorides were determined volumetrieally andgravimetrically tJy known methods. The IR spect-ra (4000-400 cm - I) were recorded as KBr discson a Pye-Unicam SP3-300 spectrophotometer.The electronic spectra of compounds in DMSOwere recorded on a Pye-Unicam 8800 spectro-photometer at room temperature. The EPR spect-

NOTES 73

Table I-Analytical data of the macrocyclic ligands and their complexes

Compounds m.pt l1.ft. Colour Found (Calc.), % m/z UVspectra Molar(0C) (BM) Found A.m•x (em - I) conduct.

M Cl C H N (Calcd) ern- ohm-Imol-I

Ligand (~) 135 white 57.4 8.2 21.6 251(57.1) (7.9) (22.2) (252)

Ligand (L;) 138 white 56.8 8.5 21.9 251(57.1) (7.9) (22.2) (252)

cu.ci, 180 4.79 green 12.9 18.5 38.1 5.4 15.2 14850 20(13.7) (18.9) (38.4) (5.3) (14.9) 32500

c-uci, 178 4.82 green 14.1 19.3 38.1 5.3 15.2 15550 19(13.7) (18.9) (38.4) (5.3) (14.9) 31800

MnLtCl2 150 5.81 light pink 14.7 18.3 38.5 5.4 15.0 22400, 18900 13(14.5) (18.8) (38.1) (5.3) (14.8) 32700

MnL;CI2 145 5.86 light pink 14.2 18.5 38.7 5.4 14.3 22550,18550 17(14.5, (18.8) (38.1) (5.3) (14.8) 32400

Fe~CI2 165 5.39 red 14.5 18.3 38.5 5.3 14.9 11400 26(14.8) (18.7) (38.0) (5.3) (14.8) 33000

FeL;CI2 163 5.43 red 15.,1 19.3 37.8 5.2 14.8 11850 20(14.8) (18.7) (38.0) (5.3) (14.8) 32800

[N~lCI2 210 light 15.7 18.9 37.0 5.3 14.3 15100,20300 98yellow (15.4) (18.6) (37.7) (5.2) (14.6) 32700

[NiL;lCI2 207 light 15.9 17.9 37.2 5.2 14.8 15900,19400 118yellow (15.4) (18.6) (37.7) (5.2) (14.6) 32900

Cu~CI2 160 1.73 light blue 16.9 18.3 37.4 5.3 14.8 16200,18100 16(16.4) (18.4) (37.3) (5.2) (14.5) 32100

CuL;Clz 155 1.75 light blue 16.0 18.2 37.8 5.1 14.0 15450,18600 18(16.4) (18.4) (37.3) (5.2) (14.5) 32400

Z~Clz 140 white 16.2 17.8 37.7 5.0 14.8 17(16.8) (18.2) (37.1) (5.1) (14.4)

ZnL;CI2 142 white 17.1 18.6 37.5 5.1 14.2 24(16.8) (18.2) (37.1) (5.1) (14.4)

ra were recorded on a Jeol JES RE2X EPR spec-trometer. The magnetic susceptibility measure-ments were carried out using a Faraday balance at25°C. The electrical conductivities of 10 - 3 M so-lutions in DMSO were obtained on a Systronicstype 302 conductivity bridge equilibrated at25 ±0.01°C.

Results and discussionThe results of elemental analyses and molecular

ion peaks in the mass spectra (Table 1) supportstheir proposed macrocyclic ligand framework(Scheme 1) derived from the condensation of 1,2-diaminoethane with alkylacetoacetate. The ligandis found to be colourless, crystalline solid. Thecomplexation of these macrocyclic ligand L, andL; gave the complexes of the types [~CI2) 01[ML;C12) for M=Cr(ll), Mn(ll), Fe(ll), CU(ll),Zn(ll) and [~)Cl2 or [ML;)Cl2 for M = Ni(ll).The analytical data of these complexes suggesttheir 1:1 metal to ligand stoichiometry (Scheme1). The molar conductivity values for all the com-

74 INDIAN J CHEM. SEe. A, JANUARY 1995

plexes except nickel in DMSO medium are in therange of 13-26 ohm - 1 ern? mol- 1 suggesting themto be non-electrolytes while that of nickel com-plexes observed in the range 98-118 ohm - 1 cm2mol- 1 suggest their 1:2 electrolyte nature 14.

The preliminary identification of the macrocyc-lie ligands have been obtained from their IRspectra which show the absence of uncondensedfunctional groups (NH2, 0 - R) stretching modesof starting materials and the appearance of bandscharacteristic of imine and amide groups. The ap-pearance of a strong absorption band in the re-gion 1635-1650 cm-I corresponds to C=Nstretching frequency. In addition to it, four amidebands have also been identified which appearedin the regions 1695-1725, 1510-1530, 1250-1280and 635-670 em -I assignable" to amide I, amideII, amide ill and amide N vibrations, respectivelysimilar to that reported for different tetraaza mac-rocyclic ligands. A single sharp band observed forthe ligands in the region 3310-3330 cm "! corre-sponds to vN - H assigned for secondary amine".The absorption bands in 2870-2960 and 1410-1465 cm-I region in all the ligands may, reason-ably, correspond to CH stretching and CH bend-ing vibration modes, respectively.

The major changes noticed for the IR spectraof the corresponding macrocyclic complexes arethe red shift in the vC = N and vNH modes whichappear in the regions 1605-1620 and 3270-3300em - 1, respectively. However, the positions ofthese bands are consistent with those reported'?for the analogous complexes. The negative shift invNH mode along with the appearance of a newband in the region 420-455 cm -1 assignable tovM - N vibration suggest that the amide nitrogenis coordinating to the metal ions. The position ofamide I band which does not undergo any changeand the absence of a band attributable to vM - 0vibration indicate that the amide oxygen is non-coordinating.

The X-band EPR spectra of the polycrystallinecopper complexes have been recorded at roomtemperature which exhibit an axial type of signalwith two g values. All the complexes exhibit simi-lar patterns of absorption with a single broad sig-nal. However, no complex is found to give hyper-fine splitting which may be due to the strong dip-olar and exchange interactions between copper(II)ions in the unit cell." In dX2 _ yl ground state, theEPR spectrum indicate that gll> g.l > 2.03 in mostcases while a dZ2 ground state usually'? gives aspectrum with g.l > gll> 2.0. The diamide macro-cyclic complexes studied here gave gll values at2.23 and 2.20 and g I values at 2.10 and 2.09 for

the complexes [Cu~ Cl2J and [CUL'lC12]respec-tively which indicate an essentially dx' _ yl groundstate for the copper(lI) ion. The axial spectrumwith gll> g.l > 2.04 is consistent" with distortedoctahedral structure around C112+ ion. It has beenreported 2I that the gll value in a copper(lI) com-plex can be used as a measure of the covalentcharacter of the metal-ligand bond. If this value ismore than 2.3, the environment is essentially ionicand values less than this limit are indicative of acovalent environment. The gllvalues for the pres-ent complexes show considerable covalent charac-ter. In an axial symmetry, the g values are relat-ed22 by the expression G = (gll- 2)/(g.l - 2), whichmeasures the exchange of interaction betweencopper centres in the polycrystalline solid. IfG> 4, the exchange interaction is negligible and ifG < 4, it indicates considerable exchange interac-tion in the solid complexes. The calculated G va-lues appeared in the range 2.22-2.30.

The IH NMR spectra of the macrocyclic li-gands do not show any signal which is attributableto primary amino protons suggesting that the pro-posed macrocyclic skeleton have been formed bythe condensation reaction. The 1H NMR spectraof the macrocyclic ligand show singlet at 1.55-1.60 and 2.05-2.28 ppm corresponding" to CH3(6H) protons and CH2 (4H) protons of alkylacet-oacetate, respectively. The IH NMR spectra of L,or L;. show a broad signal observed in the region7.51-7.90 ppm which may be assigned'" to amideprotons (2H). A singlet observed at 3.10-3.15ppm may be assigned to CH2 (8H) protons ot di-aminoethane moiety.

The IH NMR spectra of all the macrocyclicnickel(II) and zinc{II) complexes gave singlets at1.59-1.68 ppm and 2.14-2.30 ppm attributable toCH3 (6H) protons and the methylene protons(4H) of alkylacetoacetate moiety, respectively.The complexes [N~]CI2' [NiL;]CI2, [Z~CI2] and[ZnL;CI2] gave a broad signal in the region 8.01-8.23 ppm which can be attributable to amide pro-tons (2H). A singlet observed at 3.14-3.21 ppmfor all the complexes may be assigned to methy-lene protons adjacent to nitrogen. The shift of thesignals towards lower field is an identification ofthe coordination of the macrocycles.

The observed magnetic moment values (Table1) for Cr{II} macrocyclic complexes and a weakband in their electronic spectra at 14850-15500em-I region may be assigned to 5Eg -+ 5 Tzg trans-itions which are consistent" with the octahedralgeometry around Cr(II} ion. However, the ligandfield spectra of Mn{II} complexes exhibit twobands in the region 22,400-22,550 and 18,550-

18,900 em - I which are assignable to 6A'g -+ 4 ~g

and 6Alg -+ 4 T,.g transitions, respectively suggest-ing25 an octahedral environment around Mn2 +

ion. The electronic spectra of Fe(II) macrocycliccomplexes exhibit a weak intensity band at11,400-11,850 ern - I region which may reasonablybe assigned to 5 ~g -+ 5Eg (Table 1) consistent withan octahedral geometry around Fe(IJ) ion.

The magnetic moment measurements for themacrocyclic nickel(II) complexes suggesr" thatthey exhibit a square planar geometry around themetal ion. This has been further confirmed by theappearance of two bands in their electronic spect-ra in the regions 15,100-15,900 and 19,400-20,300 em - I which may reasonably be assigned

IA 'B d IA I .1 •.to . Ig -+ Ig an Ig -+ • "2g transiuons, respect-ively. The observed magnetic moment values ofthe macrocyclic copper(IJ) complexes (Table I)and the bands observed in the electronic spectracentered in 15,450-16,200 and 18,100-18,600em - I regions assignable to 2 Big -+ 2 B2g andI Big -+ 2 Eg transitions, respectively suggest" a dis-torted octahedral geometry for Cu(U} ion. All thecomplexes show bands - 33,000 em - I whichmay be due to charge transfer transitions.

AcknowledgementOne of us (SPV) is thankful to the CSIR, New

Delhi, 4>r financial support. We thank Dr IstiaqueAhmad] (GNDU, Amritsar) and Dr S I Khan(CDRI, Lucknow) for providing IR, IH NMR andelemental analysis facilities. .

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