368

hi her stability than the latter systems. ~his type bofIg . . I' -william series may e

observatlOn agamst rv1Og·d· the differentd for by consi enng .

accounte Z (II) and Ni(I1) in theirgeometrical preference of n f Z (II)complexes. The tetraltedral arrangemen~ 0 n bl

. ibili d more lavoura eleads to an increase 10fle~1 \~y ':::ixed metal speciesmolecular arrangement 10 e

lik . the Ni(I1) system which prefers a squareu~a~:r I~eometry. Similar trends have also beenp l' 167observed ear rer ...

His with Cu(ll)-Ni(ll). Cu(ll)-Zn(ll) and

Ni(ll)-Zn(ll) d the heterobinuclear complexThe first stu. y.on was carried out by Amico et

formation of HIs l~gand. t' on differs from the typesal.22.The present 10vestlga I s as re orted earlier22.~f thE' mixed metal comple~~ , • P II l\A' and

. 1 f log ~ in the. twice the va ue 0 MA rM'summ10g ~p m20and the value oflog l\.MAM(Il)-glyc1Oe(A) syste 9.15 and the valuesin the M (Il)-imidazole(A) syst~m h rimentalobtained are in agreement with t e exv.e. evalues. The deprotonation of the p~rrol.e gro~p Itno~~e

.' d in MA M' species gives nseof the I:IISh~~;(AH )M' in the title-systems. As information 0, s ecies it Ican be expected that in ~hethe MA2M P d . both the ligands bindb d rotonate species, .

a ove ep. M (= Cu(Il)/Ni(Il)) in a glycine-hkethe metal Ion His binds M' through imidazolemanner and one d HI's(deprotonated)d the seconN-ato~ an. h rrole N-atom. Thecoordmates It throug py . b th the Hisdeprotonation of the pyrrol~ group 10 of the metal

• < H of6 510 presence 0ligands begins at ~Pd' . es rise to the formationions Cu(n) and.~I(~~ea~ur;~)_His_Ni(Il) system ..Inof CUA2!"i- 2NI Ir;r u ds bind Cu(n) in a glyc10ethis species, both . IS}~a~ ..~~n.JP N atoms of the

Indian Journal of ChemistryVol. 34A. May 1995, pp. 370-374

Synthesis and characterization of binuclear metal complexesderived from some isonitrosoacetophenones and benzidine

N V Thakkar" & S Z Bootwala

Inorganic Chemistry Division. The Institute of Science. Bombay 400 032

Received 17 February 1994; revised and accepted 18 October 1994

The complexes of Coill), Ni(II) and Cu(II) with 2-hydroxyimino-l-[p-aminobiphenylimino)-1-(4'-X-phenyl)glyoxal (X=H, Cl, Br, CH3), abbreviated asp-X-HABPG, have been synthesised in situby the reaction of isonitrosoacetophenones, benzidine and metal chloride. The complexes have beencharacterized by' various physicochemical methods. The analytical data correspond to the generalformula M2LzCl2 AH20 [M = Co(ll), Ni(II) and Cu(Il)). The electrical conductance in nitrobenzene so-lution indicates their non-ionic nature. The room temperature magnetic susceptibility measurementssuggest an octahedral geometry for all the complexes, which is further supported by their diffuse ref-lectance spectra. Various ligand field parameters have been calculated for Co(II) and Ni(II) com-plexes. The infrared spectra of the complexes indicate bonding through imino and oximino nitrogenand also shows involvement of the terminal-Nl-I, group in coordination to the metal.

Studies on metal complexes with tridentate andtetradentate ligands have attracted much attentionduring recent years because of their novel stereo-chemical features. Schiff bases derived from ace-tylacetone and benzidine are well known!". Themetal complexes of schiff base ligands bis(salicyl-aldehyde )-benzidine4 and bis(benzoin )-benzidine5

are reported. In view of interesting ligating be-haviour of such systems, we considered it worth-while to prepare Co(II), Ni(II) and Cu(II) com-plexes of tridentate ligands 2-hydroxyimino-1-(p-.aminobiphenylimino )-1-(4'-X-phenyl )glyoxal (X =H, CI, Br, CH3), hereafter abbreviated as p-X-HABPG (HL), derived from isonitrosoaeeto-phenones and benzidine. The complexes havebeen characterized by various physicochemicalmethods.

Materials and MethodsAll the chemicals used were of AR grade. Ben-

zidine (Renal, Hungary) was recrystallised beforeuse, while the solvents were purified and doublydistilled before use.

Isonitrosoacetophenone was prepared as perthe procedure reported by Welcher". The p-substituted isonitrosoacetophenone derivativeswere prepared in a similar manner using approp-riately substituted acetophenones and n-butyl ni-trite. The metal complexes were prepared in situas follows: isonitrosoacetophenones and benzi-dine were refluxed in ethanol in 1 : 1 molar ratio

for six hours. After cooling the reaction mixture,metal chloride (1 : 1 molar proportion) in ethanolwas added dropwise with stirring, when metalchelates precipitated out. The products were fil-tered, washed with ethanol and Et20 and finallydried in vacuo.

Metal contents in the complexes were estimatedby standard methods. Conductance values weremeasured in nitrobenzene (10-3 M solution). Theinfrared spectra were recorded in KBr disc on aPerkin Elmer FTIR spectrophotometer model1600. The reflectance spectra of the complexes inthe visible range were taken on a Carl-ZeissVSU-2P Jena spectrophotometer. The magneticsusceptibility measurements were carried out byGouy method using Hg[Co(SCN)4] as a calibrant.The ESR spectra of Cu(II) complexes were re-corded on a Varian-E line, E-112 electron spinresonance spectrometer using TCNE as the stand-ard. Thermogravimetric studies of the complexeswere made from room temperature to 300°C at aheating rate of lOoC per minute.

Results and DiscussionThe complexes are brightly coloured and ther-

mally stable (at least upto 200°C) solids. They areinsoluble in water and common organic solvents,but are somewhat soluble in DMF and nitroben-zene at room temperature. The analytical data ofthe metal complexes (Table 1) indicate that thecomplexes have 1: 1 metal-ligand stoichiometry

lHAKKAR et al.: SYNTHESIS OF BINUCLEAR COMPLEXES DERIVED FROM ACETOPHENONES & BENZIDINE 371

Table l=-Analyttcal and physical data of metal complexes

Complex Colour Found (Calc.), % Iloff.(dec. pt, "C)

M C N H CI(B.M.)

[Co2(ABPGhCI2.4H2O] Reddish- 12.83 53.64 8.93 4.62 8.05 4.00

(200) brown (13.24) (54.00) (9.45) (4.30) (7.98)

[Co2(CI.ABPGhCI2·4HzO] Reddish- 11.89 50.24 8.53 4.08 13.93 4.10

(210) brown (12.29) (50.11) (8.74) (3.99) ( 14.81)[Co2(BrABPGhCI2.4HzO] Brown 10.94 44.92 8.26 3.57 3.92

>(280) (11.25 ) (45.86) (8.02) (3.66)

[Coz(CHJ'ABPGhClz·4HzO] Reddish- 11.89 55.04 9.03 4.65 8.13 4.12

(220) brown (12.84) (54.97) (9.16) (4.83) (7.73)

[Niz(ABPGhClz.4H2O] Yellow 13.64 53.82 9.26 4.82 8.02 2.83>(300) (13.20) (54.03) (9.45) (4.53) (7.98)

[Niz(CI.ABPGhClz·4HzO] Orange 12.86 49.98 8.25 3.89 14.89 2.81>(280) (12.25) (50.14) (8.77) (4.21) (14.13)

[Niz(BrABPGhClz.4HzO] Yellow 10.85 44.96 7.96 3.26 3.02>(290) (11.21 ) (45.88) (!:!.O3) (3.66)

[Niz(CH)ABPGhClz.4HP] Yellow 12.20 55.23 8.95 4.26 7.53 2.84>(300) (12.80) (54.99) (9.16) (4.83) (7.74)

[Cu2(ABPGhClz.4HzO] Dark- 14.33 53.26 9.26 4.68 8.02 1.80(220) brown (14.14) (53.45) (9.35) (4.48) (7.89)

[Cu2(CI.ABPGhCI2.4HzO] Dark- 13.62 50.00 8.26 4.00 15.00 1.89

>(225) brown (13.13) (49.63) (8.68) (3.96) (14.66)

[Cu2(Br.ABPGhCI2·4H2O] Brown 1\.89 45.82 8.00 3.45 1.88

>(240) (12.02) (45.46) (7.95) (3.62)·[Cu2(CH).ABPG}zClz.4HzO] Brown 13.52 54.92 9.36 4.28 7.95 1.84

>(230) (13.71 ) (54.20) (9.07) (4.78) (7.65)

.and can be formulated as. M2~CI2.4H20 whereM = Co(II), Ni(II) and Cu(II) and 'L' representsdeprotonated ligand, i.e., (p-X-ABPG). The molarconductance values for the complexes in nitroben-zene at 10-3 M dilution are in the range of 4.43-9.74 ohm-I em? mol-I suggesting non-electrolyt-ic nature of these complexes", The ligands havethree coordination sites but involvement of all thethree donor atoms in bonding to the same metalion in the complexes is sterically not favourable.However linear dimers=" are possible. The prob-able structures of the complexes may be repre-sented as shown in I.

Since none of the ligands could be isolated inthe free state, the task of interpreting the infraredspectra without ambiguity is rendered somewhatdifficult. However, several structurally significantvibrational bands have been evaluated on the ba-sis of the infrared spectra of related compoundslike iminocomplexes of some carbonyl oximes 10. 11 ,

isonitrosoacetophenones 12 and benzidine u. Somecommon features of the infrared spectra are note-worthy:

(i) The strong band due to C = 0 stretchingvibrations, seen around 1660-1680 cm - 1 in ison-itrosoacetophenones 12, is absent in all the metalcomplexes; this confirms the successful replace-ment of the carbonyl oxygen by imino nitrogenduring schiff base formation.

(ii) Since two types of C = N groups (azorne-thine and oximino) are present in the complexes,

372 INDIAN J CHEM. SEe. A, MAY 1995

Table 2-Diffuse reflectance spectral data of Co(II) & Ni(lI) complexesComplexes 4TI,(F)_4T2,(F) 4TI,(F)_4Az,:(F) 4TI,(F)_4TI,(P) Dq B {J V2/VI

(VI) (v2) (V.1)[Co2(ABPG}zCI2.4H2O] 9.090 17.857 18.518 859.3 802.6 0.826 1.96

(9.262)[Co2(CL.ABPG}zCI2·4H2O] 6.896 14.705 19.230 794.4 892.1 0.918 2.13

(14.840)[Co2(Br.ABPG}zCI2·4H2O] 7.407 15.873 20.000 846.6 824.5 0.849 2.14

(18.716)[Co2(CH3.ABPG}zCI2.4H2O] 7.142 15.384 23.809 824.2 955.0 0.923 2.15

(20.367)

Complexes JA2,(F)-JT2,(F) JA2,(F)_3TI,(F) JA2,(F)_3TI,(P) Dq B {J V2/VI

(VI) (v2) (v3)

[Ni2(ABPG}zCI2.4H2O] 9.090 14.285 23.809 909.0 721.6 0.693 1.57(9.184) (14.370)

[Ni2(Cl.ABPG}zCI2.4H2O] 10.204 15.625 27.770 1020.4 852.6 0.819 1.53

(9.403) (13.223)[Ni2(Br.ABPG}zCI2.4H2O] 10.309 16.949 25.641 1030.9 777.5 0.746 1.64

(10.424) (17.295)[Ni2(CH3.ABPG}zCll·4HzO] 10.000 16.666 26.315 1000.0 865.4 0.831 1.66

(10.703) (18.773)

Table 3-Diffuse reflectance spectral data for Cu(lI) complexes

Complex

[Cu,(ABPG}zCI2·4H20]

Band

13.89015:15118.18123.80914.92518.18125.00015.62518.51826.31515.15117.85724.390

Assignment2BI,_2B

28

'B18 - 2AI8

'Blg-'Eg

Charge transfer2BI,_2Bl,

2BI,_2E,

Charge transfer'Blg_2B2g

2BI,_2E,

Charge transfer

'BI8-2B282BI,_2E,

Charge transfer

the spectra are expected to show two VC-N

modes. These are observed between 1495 and1610 cm-I. The bands around 1570-1610 cm-Iare assigned to the azomethine group, whereasthose around 1495-1595 cm-I are attributed tooximino C = N vibrations.

(iii) All the complexes show two sharp bands inthe region around 3200 and 3300 em - I whichare attributed to symmetric and asymmetric vN - H

stretching vibrations of the - NH2 group. Thesevibrations seem to have undergone a shift .of 90-120 cm-I as compared to vsym (3320 cm-I) andvas m (3390 em -I) N - H modes of benzidine I 3 •

(lvJ A new medium to strong intensity band ob-served in the region 1195-1275 em - I in thespectra of all the complexes is ascribed to vN - 0

appearing due to the formation of N - 0 linkagein the complexes 14. This is indicative of bondingthrough oximino nitrogen atom, leading to a five-membered chelate ring formation. Bondingthrough oximino oxygen donor, leading to forma-tion of a six-membered chelate ring in a symmet-rical or asymmetrical structure, is ruled out asvN-'O due to O-coordinated oximino group'", ex-pected to occur around 1000 em - I, is not ob-served in the present cases.

(v) All the metal complexes also show a broadband around 3340-3440 em -1, which has signifi-cantly different characteristics from the band dueto hydrogen bonded VNOH vibrations observed forisonitrosoacetophenone". This band is, therefore,attributed to stretching modes of water molecules.Their centre of gravity near 3400 em - I impliescoordination of water molecules to the metalion'", This view is further supported by the ap-pearance of a band corresponding to vM-O (430-490 em - I)in the complexes.

THAKKAR et al.: SYNTHESIS OF BINUCLEAR COMPLEXES DERIVED FROM ACETOPHENONES & BENZIDINE 373

Table 4-ESR spectral parameters of Cu(II) complexes

Complexes g~ gll gay a2 A,' All X 1O~4 Gcm~l cm-1

[Cu2(CI.ABPGhClz.4HzO] 2.0176 2.0955 2.043 0.4146 180.42 92.81 5.426[Cu2(Br.ABPG)2CI2.4H2O] 2.0240 2.0955 2.043 0.3402 204.85 88.05 4.370

[Cu2(CHj.ABPG)zCI2.4H2O] 2.0200 2.0890 2.043 0.3816 177.41 87.77 4.320

•

(vi) The infrared spectra also indicate thatVC~N (azomethine) is affected by substitution inthe phenyl moiety of the parent ligand. In the me-tal chelates there are both a and n interactionsand VC~N (azomethine) decreases in the orderCH3 > H > Cl > Br which is consistent with theHammett's a values": The electron releasing sub-stituents like methyl tend to increase the electrondensity on the nitrogen of C = N, thereby facilita-ting strong a and poor n interactions.

(vii) In addition to the above bands, medium toweak intensity bands are observed around 515-618 and 360-380 em - I which may be assigned asvM - Nand vM - CI in the complexes ..

The magnetic moments of Co(II), Ni(II) andCu(II) complexes are in the range 3.9-4.1, 2.8-3.0and 1.78-1.89 B.M. respectively and are consist-ent with their proposed octahedral configurations.The diffuse reflectance spectra of Co(II) com-plexes exhibit three bands in the range of 6.89-9.09, 14.70-17.87 and 18.51-23.80 kK which maybe ascribed to the allowed transitions 4 To, g( F) -4~g(F) (VI)' 4TIg(F)_4A2g(F) (v2) and 4T,g(F)-4 TIg(P) (v3) respectively, characteristic of octahe-dral geometry. Ni(II) complexes shows the d-dtransition bands in the region of '9.09-10.30,14.28-16.94 and 23.81-27.77 kK which are as-signed "as 3A (F)_3T (F) (v) 3A (F)_3T,2g 2g I '2g Ig(F) (v2) and 3A2g(F)- 3 TIg(P) (v3) transitions re-spectively. Various ligand field parameters likeDq, B' and /3, calculated on the basis of equationsgiven by E, Konig!", and value of V/VI are givenin Table 2. These are consistent with the pro-posed octahedral structures from Co(II) and Ni(II)complexes. the energies of the transitions V I, v2or V3 have also been calculated'? and are in fairagreement with the experimental values.

In the present Cu(II) complexes, of the threebands 2 Big - 2 B2g, 2 BIg - 2 Aig and 2 BIg- 2 Eg ex-pected for octahedral Cu(II) complexes-P'-", thelatter two transitions merge and only two bandsappear in the region 13.89-15.62 and 17.85-18.51 kK (Table 3). In addition to these bands, aband in the region 23.00-26.00 kK is observedwhich is attributed to a charge transfer transition.

1 [Cu2IBrABPG12CI24H20]

2 [Cu2 (CH] ABPG12CI24H20]

3 [Cu2ICIADPG12CI24H20]

At room temperatureField set 20006

. ,,I: ,

1:: _._.-1------ -- ----- -- - --- - - -- - - ---- -- - ---- -----~._._._._._. __ ._._._._._._._._.~.\\:\ \ -------

y~'-2000 3000 3500 40002500

nm

Fig. l-ESR spectra of Cu(IJ) complexes

Unfortunately, it is not possible to determine thevalue of the interelectronic repulsion parameters,since all the d-d transitions take place within thecomponents ofthe same free ion 2 D term 23.

The high decomposition temperatures(> 200°C) of the binuclear complexes indicatestronger metal-ligand bonding. The observed ther-mal stabilities are in the order of Ni > Cu > Co,consistent with the observation by Goodwin andBailar". In the Ni(II) and Cu(II) complexes, themass loss starts at 130°C and there is sharp in-flexion between 150°C and 180°C with a massloss of 6.0-8.0% indicating the presence of fourwater molecules that are coordinated to metal ion.In case of Co(II) complexes, a mass loss of-7.0-8.2% in the temperature range 120-150°C corre-sponds to the loss of four coordinated watermolecules (calculated mass loss is 6.8-8.0%).

The room temperature ESR spectra, recordedon polycrystalline Cu(U) complexes, are shown inFig. 1. The various ESR parameters are summar-ized in Table 4. The observed gll values are lessthan 2.3 in agreement with the covalent characterof the metal-ligand bond ". The trend gll > g.L > ge(2.0023) observed for these complexes shows thatthe unpaired electron is localized in. d, _y' orbi-tal of the Cu(II) ion and the spectral features arecharacteristic of axial symmetry; tetragonally elon-gated structure may be assumed for these Cu(II)complexes.". The axial factor G (given by gll - 21g.L - 2) for these complexes is greater than 4, in-

374 INDIAN J CHEM. SEC. A, MAY 1995

dicating absence of exchange coupling-s. The a 2

values obtained from Kivelson and Neiman'sequation-" suggest appreciable covalency in thesecomplexes. It is important to note that All value isnearly half of the monomer value; such a situationis expected for Cu dimer'", The covalent naturecan also be ascertained from the value of spin-or-bit coupling constant A.'. For octahedral d? ion,E ground term can occur. The spin-orbit inter-action with higher T2 term of the same multipli-city gives the following gav value".

gav = 2.00(1- 2 A.'/10 dq) ... (1)

The gav value is obtained from the equation&v = 1/3 (gll+ 2g.l) and 10 Dq from the electronicspectrum. From Eq. (1) the A.' values were calcu-lated. The lower A.' values for the Cu(II) com-plexes compared to that of the free ion( - 830 em - 1) also suggest a considerable orbitaloverlap.

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