Indian Journal of ChemistryVol. 35A. August 199'6, pp. 681-686

Synthesis and spectral studies of copper(II) and nickel(II) complexes ofisomeric and heterocyclic benzoylhydrazones

Sayaji Rao & K Hussain Reddy"Department of Chemistry, Sri Krishnadevaraya University, Anantapur 515003

Received 11 October 1995; revised 19 February 1996

Copper(II) and nickel(II) complexes of benzoic acid [(furan-2-yl)methylene]hydrazide (BFMH),benzoic acid r 1-(furan-2-yl)ethylidene]hydrazide (BFEH), benzoic acid [(thiophen-2-yl nnethylene hydrazide \HTMH), benzoic acid ll-(thiophen-2-yl)ethylidene]hydrazide (BTEH), 2-fu-ranyl carboxylic acid (benzylidenejhydrazide (FCBH) and 2-thiophenyl carboxylic acid (benzyli-dene)hydrazide (TCBH) have been synthesized and characterized by elemental analysis, conductivity,magnetic susceptihility measurements, JR, electronic and ESR spectral data. The electronic spectraldata and the magnetic moment value suggest an octahedral structure for all nickel(II) complexes,planar geometry for copper complexes of BFMH, HTMH, FCBH and TCBH ligands and an octahe-dral geometry for the copper{II) complexes with BFEH and BTEH ligands.

Schiff base metal complexes have broad applic-ations in hiological processes I.~ and as catalyst inchemical and petrochemical industries-'~. Hetero-cyclic aroylhydrazones are known to react withdivalent transition metal ions forming both cation-ic and neutral metal chclatcs of the general for-mulae M(LH), X, and ML (where LH = hetero-cyclic aroylhydrazones) respectively with the he-terocyclic aroylhydrazone acting as a neutral ormono negative hidentate ligand). Recently, com-plexes of hydrazones containing furan- 2-carbox-aldehyde residue have been reported":". It shouldhe of interest to study hetero-donor ligands withisomeric formulae as these complexes are expect-ed to show interesting structural and functionalproperties. For this reason we have studied com-plexes of heterocyclic aroylhydrazones viz., ben-zoic acid [furan-z-yllmethylenejhydrazide (I,BFMH), benzoic acid [1-(furan-2-yl)ethylidene]hydrazide (II, BFEH), benzoic acid[1-(thiophen- 2-yl )methylene ]hydrazide (III,BTMH), benzoic acid [1-(thiophen- 2-yllethyli-dene]hydrazide (IV, BTEH), 2-furanyl carboxylicacid (benzylidene)hydrazide (V, FCBH) and 2-thi-ophenyl carboxylic acid (benzylidene )hydrazide(VI, TCBH). In continuation of our studies onmetal complexes of heterocyclic hydrazones", her-ein we report the synthesis, magnetic and spectralstudies of copper(II) and nickel(II) complexes ofthese hydrazones. It may be noted that I and V orII and VI are isomeric Iigands.

Materials and MethodsFurfuraldehyde, 2-furyl methyl ketone, thio-

phcnc-Lcarboxaldehyde, 2-acetyl thiophene andbcnzhydrazide were of reagent grade and pur-chased from Mis Fluka. 2-Furoic hydrazide and2-thiophene carboxylic hydrazide were suppliedhy Mis Aldrich Chemical Co. The solvents usedfor the synthesis of ligands and their copper com-plexes were distilled before use. All other chemi-cals were of reagent grade quality and used with-out further purification.

Preparation of the ligandsRFMH, BFEH, BTMH, BTEH(HV)

Hot aqueous solution (6.8 g, 0.05 mol) of ben-zylhydrazide was added to a boiling solution ofcarhonyl compound (0.05 mol) in methanol (200ml), The reaction mixture was boiled under refluxfor 1 h. A pale yellow coloured crystalline pro-duct was formed on cooling the reaction mixture.This was collected by filtration, washed several

I x:o, R=H (BFMH)II x=o, R=CHj(9fEH)

III x=s, R=H (BTMH)IV X=S, R=CH3(BTEH)

v X=O (FC BH)VI X=SCTCBH)

682 INDIAN J CHEM, SEe. A AUGUST 1990.

times with hot water and dried in vacuo. These li-gands were recrystallized from methanol.

FCBH and TCBH(V andVI)A reaction mixture containing benzaldehyde

(5.3 g, 0.05 mol) and 2-furoic hydrazide (6.3 g,0.05 mol) or thiophene-2-carboxylic hydrazide(7.1 g, 0.05 mol) in 200 ml of ethanol was boiledunder reflux for 5 h. On cooling a pale yellow co-loured product was formed which was collectedby filtration, washed several times with hot waterand dried in vacuo. These ligands were also re-crystallized from methanol.

Preparation of complexesThe complexes were prepared by nuxmg hot

aqueous solution of hydrated metal salts [CuCl26H20, NiCl2 6H20] and ligands (I-VI) in the mo-lar ratio of 1:2.

To the boiling solution of ligands (0.01 mol) inmethanol (100 ml), was added hydrated metalsalts (0.05 mol) dissolved in minimum quantity ofwater and heated under reflux for 2-6 h. Crystal-

line complexes which separated out were collect-ed by filtration, washed with hot water, smallquantity of methanol and hexane and dried invacuo. The analytical data of the ligands and theircomplexes are presented in Table 1.

The elemental analyses were performed at theRSIC, CDRI, Lucknow. Magnetic measurementswere carried out in the polycrystalline state on aPAR model 155 vibrating sample magnetometeroperating at a field strength of 2 kG to 8 kG.High purity nickel metal (saturation moment 55emu/g) was used as a standard. The molar con-ductance of the complexes in DMF (10-3 M) so-lution were measured at 27 ± 2°C with a SystronicModel 303 direct reading conductivity bridge.The electronic spectra in nujol were recordedwith Cary Model 2390 spectrophotometer and inchloroform and DMF with Schimadzu UV-160Aspectrophotometer. The infrared spectra were re-corded in the range 4000-180 em - I with a PerkinElmer 983 G spectrophotometer. The IH NMRspectra were recorded on Varian XL-30n MHzhigh resolution instrument in CDCI, solvent. The

Table I-Analytical data of ligands and their Cu(II) and Ni(lI) complexesLigand/Complex Colour Found (Carcd.). o/.,

(Yield,%) (M.pt..°C)C H N

BfMH Light yellow 7 67.42 4.67 13.2090 ( 151-152) (67.28) (4.67) ( 13.08)

Cu(BFMh Brown 58.1)7 3.70 11.6323 (above 250) (58.83) (3.67) (·11.43)

[Ni(BTMH)~Cl2] Orange 41).1)0 3.2040 (above 250) (51.80) (3.60)

BFEH Dark brown 67.78 5.45 12.5152 (143-145) (68.42) (5.26) ( 12.28)

Cu(BfE)2 Dark green 51).09 4.17 1).5225 (163-165) (60.28) (4.2~) ( 10.82)

BTMH Dark yellow 63.26 4.12 12.2395 (192-194) (62.60) (4.35) ( 12.17)

Cu(BTMh Brownish yellow 54.92 3.61) 1).7153 (above 250) (55.22) (3.45) (10.23)

[Ni(BFMHhCI2] Orange red 52.50 3.40 10.1056 (above 250) (48.90) (3.40) (9.50)

BTEH Yellow 64.54 4.84 11.5291 ( 197-1(9) (63.93) (4.92) ( 11.47)

Cu(BTEh Greenish brown 56.78 4.18 9.9948 (238-240) (56.77) (4.00) ( I!l.l I))

FCBH Light yellow 67.30 4.65 13.1538 (220-222) (67.28) (4.67) (13.08)

Cu(FCBh Dark brown 58.86 3.6334 (238-240) (58.83) (3.67)

[Ni(FCB)(HPhClb Orange red 42.00 3.80 7.9035 (above 250) (42.10) (3.80) (8.20)

TCBH Dark yellow 61.80 4.32 12.1037 (167-169) (62.60) (4.34) (12.17)

Cu(TCB)2 Light yellow 55.60 3.1565 (above 250) (55.22) (3.45)

[Ni(TCB )(H20 hClb Orange red 45.80 3.3050 (above 250) (45.10) (3.60)

RAO er al.: Cu(JI) & Ni(JI) COMPLEXES OF BENZOYLHYDRAZONES 683

mass spectra were recorded using Fanning Mat8230 mass spectrometer. The £SR spectra wereobtained on Varian £-112 X-band spectrometerat room temperature in polycrystalline state andin DMF at liquid nitrogen temperature.

Results and DiscussionThe analytical data (Table 1) for all ligands and

their Cu(II) and Ni(II) complexes are consistentwith their proposed molecularformulae.

The IH .NMR spectra of BFMH, BF£H,BTMH, BTEH, FCBH and TCBH in CDCl3show low field signals respectively at 011.23,11.35, 9.07, 8.91, 11.75 and 10.76 ppm for theimino protons present in ligands. In the spectra ofBFMH, BTMH, FCBH and TCBH, CH = N peakis observed respectively at 8.60, 8.80, 8.25 and8.26 ppm. Signals due to the aromatic protons oc-cur as multiplets between 06.4 to 7.4 ppm. Theresonance signal due to - CH, protons present inBFEH and BTEH occur at 02.38 and 2.30 ppmrespectively.

The mass spectra of BFMH, BFEH, BTMH,BTEH, FCBH and TCBH show molecular ionpeaks. The important peaks observed in the massspectra of these ligands are at m/e, 67, 77, 105,125, 139 and 161 respectively correspondin~ toC"HjO, C6Hs, C.H"CO, C4H,9(CH1)-C:N-NH2(BFEH), .. C4H,S( CH3) - C:N - NH2 (BTEH).C6HsCONHN:C - CH3 (BTEH).

The absorption spectra of - 2 x 10- 'i M solu-tions of the hydrazones at various pH values wererecorded. The pKa values for the deprotonationof BFMH, BFEH, BTMH, BTEH, FCBH andTCBH respectively are 3.0, 4.7, 3.7, 5.6, 6.5 and4.5 calculated from the variation of absorbancewith pH by Phillips and Merrit's method".

All the complexes are stable at room tempera-ture, non-hygroscopic, insoluble in water, metha-nol and ethanol, but soluble in DMF and DMSO.The complexes are non-electrolytes'? in DMF so-lution.

The room temperature magnetic moments arein the range 1.8-2.2 B.M. These magnetic momentvalues indicate the presence of one unpaired elec-tron as expected for copper(II) complexes.

The magnetic moments of nickel complexeswith BFMH, BTMH, FCBH and TCBH are re-spectively found to be 3.1, 2.8, 2.5 and 2.3 B.M.in.favour of an octahedral geometry.

The important electronic absorbance bands inthe spectra of complexes recorded in solution andas nujol mulls are discussed. The spectra aredominated by intense intraligand and charge-transfer bands. The spectra of Cu(BFMh,

Cu(BTM}z, Cu(FCB)2 and Cu(TCBlz complexesshow low intensity bands (£ = 710-180 L. mol- I

em - I) in the range 17860-17240 ern - I assignableto the d-d bands of planar copper(II) complexes II.

The presence of single d-d band in the electronicspectra of these complexes may be attributed tothe presence of symmetric ligand fields. From theposition of d-d bands, the stability order for thesecopper complexes may be assigned as Cu(BFMh> Cu(FCBh > Cu(BTM)~ > Cu(TCB)~.

The electronic spectra of Cu(BFEh andCu(BTE)~ complexes exhibit one broad band inthe 15870-16000 cm-I region with £=400-300L. mol- I em - I and shoulder in the 14000-14R30em - I region which are assigned respectively as2 Big ....• 2 Eli and 2 Big ....•2 Alg transitions in a tetra-gonally distorted octahedral geometry. The2 Big ....•2 B2g is usually not observe? .as a sepa~ateband in tetragonal field II. The splitting of 2Eg IS ameasure of the in-plane and axial field. Since thein-plane field is approximately constant in thepresent complexes, the change in the position ofbands would be mainly due to the axial field. Inthe complexes, Cu(BFElz and Cu(BTElz, the2Big ....•2 Aig tr.ansition is shifted to higher energy,the order being, Cu(BTE)z < Cu(BFEh.-Charge-transfer bands (L....•M) in the spectra of the com-plexes in chloroform solution are observed at26500 ern -I. However, in the solid state, thisband is observed at a higher energy, indicatingthat the deviation from a symmetric structure inthe solid state is more than in solution. Thecharge-transfer band is found to be shifted tohigher energy in the spectra recorded in DMF so-lution for these complexes possibly due to the co-ordinating nature of the solvent.

All nickeltll) complexes exhibit three bands infavour of octahedral geometry. These bands fromlower energy to hilJ;her energy are attributable to3Az, ....•3 Tz (F)(v

l); 3Az~F) ....• 3 ~~F)(V2) and

3Az; F) .!3 ~~ P}{ v3). transitions resp~ctively. Th.espectral data are utilized to compute Important li-gand field parameters (10 Dq, Band B3S) usingthe ligand field theory of spin-allowed transitionsin dB configuration II. The 10 Dq and B values areemployed to calculate V2 and V3 and the resu.ltsare given in Table 2. The ratio of v2 and VI liesbetween 1.56-1.74 range as expected for octahe-dral nickel (II) complexes'".

The ESR spectra of complexes in polycryst~-line state at room temperature show a strong SIg-nal at iigh field and a weaker one at low fieldcorresponding to g~and g!., respectively. The ob-served- values of g" > gl > '2.?O ana ~e G va-lues in range 2.2-4.1 are consistent WIth dx': _ .;.having a small exchange coupling". The gll values

684 INDIAN J CHEM, SEe. A, AUGUST 1996

for the complexes studied follow the orderCu(BTE h < Cu(BFEh. This order may be un-derstood in terms of greater covalent bondingpotential of sulphur compared to oxygen as ref-lected in its higher position in the nephelauxeticseries.

The spin Hamiltonian orbital reduction andbonding parameter of copper complexes in DMFsolution at LNT are presented in Table 3. Theanisotropic spectra are obtained for all complexesin DMF at liquid nitrogen temperature. In thislow temperature spectrum, four peaks of small in-tensity have been identified which are consideredto originate from g~ component. The gl and glare computed from the spectrum using DPPH freeradical as ~ marker. Kivelson and Neiman havereported that g~value is less than 2.3 for covalentcharacter and is greater than 2.3 for ionic charac-ter of the metal-ligand bond in complexes. Apply-ing this rule, the covalent character of the metal-ligand bond in complexes under study can be pre-dicted. The G values for all complexes are givenin Table 3. The G values in these complexes aregreater than four suggesting that there are no in-teractions between the copper centres in DMFmedium.

The ESR parameters g~,gl' Au and Al of the

complexes and the energies of d-d transitions areused13,14 to evaluate the orbital reduction narame-ters (K~, K 1), the bonding parameters (a2), thedipolar interaction (p) and the Fermi contact in-teraction term (K). The observed Ku > K 1 rela-tion indicates the presence of out-of-plane J't'-bonding". The a2 values for the present chelateslie in the range 0.83-0.87. which support the cova-lent nature of these complexes. Giordano andBereman" suggest the identification of bondinggroups from the values of dipolar term P. The re-duction of P value from the free ion value (0.036cm - I) might be attributable to the strong covalentbonding. The values of P obtained for the presentcomplexes lie between 0.018-0.021 em -I and areconsistent with bonding of copper to .ON donoratoms.

Important bands observed in the IR spectra ofthe ligands and their copper(II) and nickel(II)complexes are discussed. The donor sites of li-gands have been adduced from infrared spectralstudies. The infrared spectra of free ligands exhib-it v(NH) absorption bands at ca. 3250 andv(C=N) bands at ca. 1660 cm "! indicating thatthe ligands exist in keto form in the solid state.However, in solution and in the presence of metalions, the ligands probably exist in equilibrium

Table 2-Electronic spectral data and ligand field parameters* of nickel complexesComplex VI v2 v) Bt bv' rr;s lODq V/V2 LFSE[Ni(BFMH hC12] 10415 18180 27625 10415 1.74 29.7

(lODq) (17100) (28780) (970) (± 1155) (0.94) (10415) (1.64)[Ni(FCBXH2OhClh 9820 15105 26660 9820 1.54 28.0

(1ODq) (15811) (25949) (820) ( ±711) (0.80) (9820) (1.61)[Ni(BTMHhCI21 10415 18180 23585 10415 1.74 29.7

(10Dq) (16199) (25565) (701) (± 1981) (0.68) (10415) (1.55)[Ni(TCB)(HzOhClb 10415 17850 27320 10415 1.71 29.7

(lODq) (16921) (28249) (928) ( ±930) (0.90) (10415) (1.62)

* Calculated values are given in parenthesis, "B = (v2+v)-3vl)/15; fDifference in the observed and calculated value; **Ratioof the free ion and the complex.

Table 3-Spin Hamiltonian and orbital reduction parameters of copper complexes in DMF solution

Parameter Cu(BFMh Cu(BFE)2 Cu(BTM)2 Cu(BTE)2 Cu(FCBh Cu(TCBh

2.270 2.273 2.256 2.260 2.310 2.2402.060 2.063 2.054 2.053 2.057 2.0252.130 2.133 2.121 2.122 2.142 2.1164.61 4.46 4.90 5.08 5.66 4.760.0142 0.0135 0.0146 0.0140 0.0139 0.01460.00186 0.00186 0.0035 0.00140 0.00186 0.00560.0059 0.0057 0.0072 0.0056 0.0059 0.00860.834 0.805 0.810 0.785 0.897 0.7690.775 0.762 0.730 0.697 0.754 0.7050.852 0.843 0.846 0.840 0.872 0.6900.020 0.019 0.Q18 0.020 0.021 0.01430.576 0.580 0.516 0.398 0.416 Q.505

RAO et al.:Cu(Il) & Ni(Il) COMPLEXES OF BENZOYLHYDRAZONES 685

VII a (where. x= 0 or 5)

with tautomeric enol form. By the loss of proton,the enolic form may act as a singly-charged li-gand. The bands appearing in the spectra of theligands - 1660, 1640, 1015 em - I are attributed 17

to v(C = 0), vC = N, and v(N - N) modes respect-ively. The two strong bands observed at 710-690and 610-605 em - I regions are assigned 18 to fur-an/thiophene ring deformation modes. In the caseof [M(LH)CI2] complexes (where M = Ni(II),LH = BFMH, BTMH), the amide I and amide IIbands shift to lower frequency in the spectra ofthese complexes ..The v(C = N) shifts to lower fre-quency (~= -10 cm-I) and v(N -N) to higher(~= - 20 ern - I) frequencies, in the spectra of allcomplexes suggesting the participation II} ofazomethine nitrogen and carbonyl oxygen in co-ordination. For complexes [Cu(Llz] (where L= allligands) and [Ni(Lh(H20hCl]2 (where L= FCBHor TCBH ligands), the IR spectra lack absorptiondue to both vNH and vC = 0, but show newbands (ca. 1320 cm - I) characteristic-" ofv(N - CO). The increase in vN - N in the spectraof the complexes is due to increase in double-bond character off-setting the loss of electrondensity via donation to the metal suggesting theparticipation of azomethine nitrogen atom in co-ordination. Furan or thiophene ring deformationvibrations are not affected in copper and nickelcomplexes of BFMH, BTMH, FCBH and TCBH.The red shift of ring deformation vibrations in thecase of Cu(BFE lz and Cu(BTE lz complexes sug-gests the participation of furan oxygen and thio-phene sulphur respectively in complex formation.The highest energy band in the IR spectra ofnickel complexes with FCBH and TCBH respect-

ively are observed at 3115 and 3127 cm-I as-signed to the presence of coordinated water mole-cules.

The non-ligand bands" occurring in the region500-570 and. 385-430 ern - I are tentatively as-signed to v(M - 0) and v(M - N) modes respect-ively. The molecular weights of[Ni(FCB)(H20lzClh and ·[Ni(TCB)(H20lzCl] com-plexes are found to be 700 (686); 585 (590), asrequired for dimeric complexes.

Based on the results presented above, octahe-dral structure (VII a & b) is assigned toCu(BFElz, Cu(BTE)2' [Ni(BFMhCI2],[Ni(BTM)?Cl?1; square planar geometry forCtli.~FMh, Cu(BTM)2 and dimeric structure(VUI) for [Ni(FCB)(H20hCl]2 andlNi(tCB )(H20 hCl J2 complexes.

AcknowledgementThe authors thank CDRI, Lucknow and RSIC,

Madras, for providing elemental analysis andspectral data.

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