Indian Journal of ChemistryVol. 21A, December 1982, pp. 1110-1112

Studies in Binuclear Copper(II) Complexes of TetradentateSchiff Bases Involving Greater n-Delocalization

KALPANA V PATEL & PABITRA K BHATTACHARYA'

Department of Chemistry, Faculty of Science, M.S. University of Baroda, Baroda 390002

Received 16 August 1982; accepted 21 September 1982

Dimeric copper(1l) complexes of the type [Cu(TSB)Cu(A-A)](CI04), have been prepared, where TSB = symmetricaltetradentate schiff bases derived by the condensation of salicylaldehyde or 2-hydroxyacetophenone with o-phenylenediamineand unsymmetrical tetradentate schiff base derived by the condensation of «-phenylencdiarmne with salicylaldehyde and 2-hydroxyacetophenone and A-A = 2,2' -bipyridyl, I, IO-phenanthroline or 2-(2' -pyridyl)benzimidazole. \1agnetic susceptibilitymeasurements at room temperature show lowering in !lor, values. This is due to antiferromagnetic interaction between twononequivalent copper(II) ions. UV spectral studies indicate that the n-orbitals are not involved in superexchange interaction.

A set of bicovalent oxygen atoms belonging to atransition metal complex could be considered as a"complex ligand". This complex ligand when made toreact with a metal chloride, gives rise to a polymetallicspecies, the utilization of which could be interesting inmulticentre metal-promoted molecular activationprocesses 1.2. A number of such type of homo- andhetero-binuclear and trinuclear complexes have beenisolated and studied in detail:'. We have also isolatedhomo-binuclear copper(II) complexes involvingsymmetrical" and unsymmetrical" tetradentate schiffbases, where a second copper(II) is coordinated to atertiary diamine like 2,2'-bipyridyl (A I), 1,10-phenanthroline (A 1) or 2-(2' -pyridyl)benzimidazole(A 3) with a view to observing the effect of n-bondingtertiary amines on the magnetic properties of the bi-metallic complexes. In the case of tetradentate schiffbases obtained from aliphatic diamines, tt-

delocalization is confined to only the aromatic rings. Itis envisaged that n-delocalization wil1 spreadthroughout the tetradentate schiff base molecules, ifthe condensa tion of salicylaldehyde is carried ou t wi tharomatic diamines. It would be interesting to see theeffect of such n-delocalization on the binuclearcomplexes obtained from such tetradentate schiff basecomplexes. With this aim in view, syntheses of anunsymmetrical tetradentate schiff base complex,(N ,N' -0-phenylenesalicylaldiminato-2-hydroxyaceto-phenoniminato) Cu(II) and the binuclear complexes ofboth symmetrical and unsymmetrical tetradentateschiff base complexes are reported in this paper.

Materials and MethodsAl1 the chemicals used were of AR grade. Copper(II)

perchlorate hexahydrate was prepared by dissolvingCuCO 3 (I mol) in perchloric acid (2 mol). Symmetrical

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tetradentate schiff base complexes" and 2-(2'-pyridyl)benzimidazole were prepared by the knownmethods",

Preparation oj'(N, N' -o-phenylene-salicylaldiminato-2-hydroxyacetophenoniminato) Cr.(I l) [Cr.( TSBI)]-The preformed mixed imine schiff base complex",[(salicylaldiminato-2-hydroxyacetophenoniminato)Cu(II], (0.1 mol) in ethanol-water (I: I, v/v), wasretluxed with o-phenylenediamine (0.1 mol) for about5 hr. with intermittent stirring. The solid thus obtainedwas filtered, washed thoroughly with water fol1owedby ethanol, dried and analysed (Calc.: Cu, 16.23; N,7.15; Found: Cu, 16.54; N, 7.15~/~);/lerr=2.IOSB.M.

Preparation of binuclear complexes of type-I[Cr.(TSBI)CUX1]~To a solution of [Cu(TSB1)](0.0035 mol in 50 ml chloroform) was added a solutionof CuCl1.2H10 or Cu(CI04h.6H10 (0.003 mol in 20ml of ethanol) and the mixture retluxed for 30 min,with constant stirring. Resulting solid[Cu(TSB1)CUX1J. where X=CI- or Cl04-, wasfiltered, washed thoroughly with chloroform toremove excess of [Cu(TSB I)], dried and analysed.

Preparation of[Cr.(TSB) Cu(A-A)](CI04h type-II-To a solution of [Cu(TSB)] (0.0035 mol in 50 mlchloroform) was added a suspension of [Cu(A-A)(CI04)1] (0.003 mol in 20 ml absolute ethanol), themixture retluxed for 2-3 hr with constant stirring andthe resulting solid filtered, washed thoroughly withchloroform to remove excess of [Cu(TSB)], dried andanalysed.

Results and Discussion

The purity of the compounds was checked by TLCsilica gel plates using ethanol as developer. Onexposure to iodine vapours, only single spots were

PATEL et al.: BINUCLEAR CuOI) COMPLEXES

_._._- ----~-~---.-.--- --.----------~--.~~

Table I-Elemental Analyses and Magnetic Moments per CuOI) Ion of Binuclear Complexes

SI.No. Compound Found (Calc.). 0" !ldl/CU( II). -.--- ----- B.M .

Cu N C H

[Cu(TSB 1)CuCU 24.3 4.9 47.3 3.00 1.024(24.2) (5.3) (47.9) (3.04)

2 [Cu(TSB1)Cu(CI04),] 19.2 3.9 38.4 2.42 LOI(19.4) (43) (38.5) (2.45)

3 [Cu(TSB 1)Cu(A :J](Cl04h 15.3 6.8 46.1 2.97 LI6(157) (69) (469) (2.96)

4 [Cu(TSB 1)Cu(A ')](CI04), 14.7 6.4 48.6 2.84 L09(15.2) (67) (47.5) (2.88)

5 [Cu(TSB 1)Cu(A J)](CI04), 15.0 8.1 46.6 2.67 LOR(15.0) (82) (46.6) (2.94)

6 [Cu(TSB')Cu(A 1)](Cl04), 15.6 7.0 45.2 2.72 L06(16.0) (70) (45.2) (2.76)

7 [Cu(TSB')Cu(A ')](Cl04h 15.1 7.0 46.7 2.68 L07(15.5) (68) (468) (2.68)

8 [Cu(TSB')Cu(A J)](CI04lz 15.1 8.3 45.8 2.73 LOO(152) (8.4) (460) (275)

9 [Cu(TSB3)Cu(A 1)](CI04lz 15.0 6.7 46.5 3.20 LOS(15.4) (6.8) (46.6) (3.16)-- 10 [Cu(TSB3)Cu(A 2)](CI04lz 15.0 6.5 47.9 2.93 1.06(15.0) (6.6) (48.1) (3.07)

II [Cu(TSB3)Cu(A 3)](Cl04), 14.7 8.0 47.0 3.02 0.997(14.7) (81) (47.3) (3.13)

TSB1 refers to N, N'-o-phenylenesalicylaldehydimine-2-hydroxyacetophenonimine: TSB' to N.N'-u-phenylene-bis-salicylaldehydimine: andTSB3 to N,N'-o-phenylene-bis-2-hydroxy-acetophenonimine.

detected in all the cases. The elemental analyses (Table1) of the complexes correspond to the expectedformulae. The structure of different binuclearcomplexes obtained can be represented as follows:

Type 1 (X= Cl- or ClO4' )

,-- N~N

I ©:~~Cu~=)QJLR<Q)RType II (R= H or CH3; R'= H or CH3 "

NN = 2 , 2'- bipyridyl (AI) , 1,10-

2 'phClnanthrolim (IS. ) or 2(2'

pyridyl )oonzim'ldazolc (A3)

The binuclear complexes are not soluble enough inorganic solvents to determine their molar con-

ductance. Consequently, the ionic/non-ionic nature ofthe perchlorate was confirmed by the help of their IRspectral data 9. Bands of TSB in [Cu(TSB)] complexshow a small shift of 5-10 cm '" in the binuclearcomplexes. The vC -0 of [Cu(TSB)] shows aconsistent shift of 15-20 em -I suggesting bridgingthrough phenolic 0 (refs 10, II).

Room temperature magnetic moment, obtainedusing Gouy method, shows a significant decrease fromthe expected value of one unpaired electron over eachcopper(II) ion. Since, direct metal-metal interaction isforbidden in such complexes due to copper-copperdistance, lowering in magnetic moment can be ascribedto the antiferromagnetic superexchange interactionbetween the two nonequivalent copper(II) ionsthrough phenolate 0 - bridge.

The unpaired electron is present in each of the dXl_y'

orbitals of the two copper(II) ions and they undergo a-overlap with the filled s- and p-orbitals of the bridgingphenolic 0 - (refs 12,13), leading to superexchange andthereby lowering the Peff value. The predominance ofsuperexchange through a-interaction in such binuclearcomplexes of tetradentate schiff bases has beenconfirmed by earlier workers!" on the basis of theobservations that, (i) there is a linear relationshipbetween the magnetic moment and d-d band positionof the binuclear complex and (ii) magnetic moment

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INDIAN J. CHEM .• VOL. 21A. DECEMBER 1982

depends on 0 - Cu - 0 bond angle in the binuclearcomplexes.

Reflectance spectra of selected compounds withmagnesium carbonate as reference. reveal thefollowing characteristic features.

Binuclear [Cu(TSB1)CuCI2] displays bands at17390 and I)) 10 ern -I. The former is due to[Cu(TSB1)] moiety and latter corresponds to::;CuCI2. [Cu(TSB1)Cu(A I)] (CI04h also shows twobands at 17700 and 14810 ern -I corresponding to[Cu(TSB1)] and :::[Cu(A1)]2+ segments respectively.The> [Cu(A I)J2+ centre shows a d-d band at higherenergy (14810 em -I) than that observed for :::CuClzsegment (II 110 ern -I). This is because, tertiarydiamine can create a stronger ligand field as comparedto two chloride ions".

However, in both types of binuclear complexes theband corresponding to [Cu(TSB)] segment shows shiftfrom the free [Cu(TSB)] value of 16670 cm I. Thissignificant change in ligand field band of [Cu(TSB)] isdue to the change in its planarity due to thecoordination of ::::CuCl2 or [Cu(A 1)]2+ (refs 4.1 0).

Electronic spectra of mononuclear and binuclearcomplexes in ethanol (recorded on a specrod UV- VISCZ lena instrument with I ern quartz cell) givesfollowing information: As observed earlier":".[Cu(TSBI)Cu(A I)J (CIO .•)z exhibits bands at 47000,42000. 38000 (sh), 33250. 32000. 29000. 26000 (sh)and 24000 em -I. corresponding to the electronictransitions of [Cu(TSBI)J, i.e. 47000. 43000, 38000(sh), 33200. 29000. 26000 (sh) and 24000 cm-I

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without any significant change. This indicates that thesuperexchange interaction involves only the a-orbitalsof the metal ions and the bridging 0 -. The n-orbitalsof the two ligands are not involved in thesuperexchange process. An interaction betweentetradentate schiff base and bipyridyl (A 1) through themetal ion dn:-orbitals would have changed thepositions of the near UV bands (n-4n:*) in the binuclearcomplex.

AcknowledgementOne of us (K V P) gratefully acknowledges the award

of a senior research fellowship by the CSIR. NewDelhi.

ReferencesI Fachinetti G. Floriani C & Zanazzi P F. J Ani chem s.«. 100

(\ 97X) 7405.2 Fachinetri G. Floriani C. Zanazzi P F & Zanazari A R. lnorg

eh"III. 18 (1979) 3469.3 Sinn E & Harris C M. Coord ChI'lli Re:. 4 (1969) 391.4 Palel K V & Bhattacharya P K. J eh(,111SOl" oou.«. (1982) 359.5 Patel K V & Bhattacharya P K. Indian J chcm, 21A (1982) 674.6 Pfeiffer P. Breith E. Lubbe E & Tsumaki T. AI/I1. 84 (1933) 503.7 Waller J L & Freiscr H. Analyt Chelll. 26 (1954) 217.

8 Thaker B T & Bhauacharya P K. J inorg IIUe! c//('/IJ. 37 (1975) 615.9 Procter J M. Hathaway B J & Nicholls P J. J chcm SodA). (1968)

1768.10 Gruher S J. Harris C M & Sinn E. J inorg' nucl (hem. 30 ( 1968)

1805.II Harris C M & Sinn E. J illl"~ 11lIeI chem, 30 (1968) 2723.12 Bhattacharya P K. J Indian chem s«, S9 (19g2) 505.13 Lambert S L & Hendrickson D N./I1()"~ Chem, 18(1979) 26!D.14 Kato M. Muto Y. Jonassen H B.lmai K & Harano A. Bull chem

Soc Japan, 41 (1968) 1864.