Indian Journal of Chemistry Vol. 39A April2000, pp. 415-420

Synthesis, structure and reactivity of zirconium(IV), vanadium(IV), cobalt(II), nickel(II) and copper(II) complexes derived from

carbohydrazide schiff base ligands

D U Warad, CD Satish, V H Kulkarni & Chandrasekhar S Bajgur*

Department of Chemistry, Gulbarga University, Gulbarga 585 106, India

Received 10 May 1999; revised 20 January 2000

A series of polydentate schiff base ligands have been prepared by the condensation of carbohydrazide, H2N-NH-CO­NH-NH2, with various aldehydes and the isolated ligands characterized by elemental analysis and spectral methods. In order to investigate the coordination behaviour of these ligands, metal complexes of the type M(acac), L[M = Zr(IV), VO(IV), Co(! I), Ni(II) and Cu(II); L = Schiff base ligands; x = 0 or 2] have been prepared from the reaction of these ligands with their corresponding metal acetylacetonates. On the basis of analytical and spectral data, square antiprism, square pyrimid and square planar structures have been proposed. The biological activities of all isolated ligands and their metal complexes have been studied by screening the compounds against organisms such as E. coli, S. aureus, A. niger and C. albicans and the results have been compared.

The chemistry of carbohydrazide and thiocarbohy­drazide, H2N-HN-CX-NH-NH2 (X=O, S) compounds and some of their derivatives has been reviewed by Kurzer and Wilkinson 1

• Both hydrazine groups of these compounds display normal reactivity towards carbonyl compounds and are expected to yield mono and dihydrazone derivatives which contain N, 0 and S donor atoms and therefore the derivatives can func­tion as suitable ligands for transition metals . Variety of metal complexes of symmetrical dihydrazones de­rived from thiocarbohydrazides have been prepared and their stereochemistry have been reported in the literature? Interestingly, the coordination chemistry of the corresponding carbohydrazide derivatives is Jess explored3

. Carbohydrazide, a diamine, upon con­densation with two molecules of salicylaldehyde or substituted salicylaldehydes should give symmetrical J ,5-dicarbohydrazones, H2L.

Keeping in view the various possibilities of inter­action of these schiff base ligands with metals, efforts were undertaken to investigate the synthesis and characterization of these ligands. Further, with metal acetylacetonates, M(acac), [M = Zr(IV), VO(IV), Co(II), Ni(JD and Cu(IJ); x = 2, 4] as precursors, sev-

Tel : 08472-45982(oft), 45534(res) Fax: 08472-45632 Email : csbajgur@yahoo .corn

eral complexes of the type ML, were prepared using these ligands and have been characterized by ele­mental analysis, conductivity, magnetic, infrared, NMR and electronic spectral measurements .

Materials and Methods The salicylaldehyde_ derivative and metal ace­

tylacetonates [Zr(acac)4, VO(acac)2, Co(acac)z, Ni(acac)2 and Cu(acac)2 were prepared by known methods4

•

Preparation of ligands The pure crystals of carbohydrazide (0.01 mol) and

salicylaldehyde (0.02 mol) were mixed in alcohol medium and the mixture reffuxed for about 4 h.The product formed was suction filtered and recrystallized from ethanol (yield 90%, m.p. 216°C). Other car­bodihydrazones were prepared by similar procedure using substituted salicylaldehydes.

Preparation of metal complexes Preparation of zirconium( IV) complexes

To a dry methanolic solution (0.01 mol) of bis(salicylaldehydo )-1 ,5-carbohydrazone, was added (0.01 mol) zirconium acetylacetonate dissolved in 20 mL of dry methanol, drop-wise, with constant stir­ring. The stirring was continued for 4 h. The precipi­tated complex was filtered, washed with 5 mL of

416 INDIAN J CHEM, SEC. A, APRIL 2000

methanol and dried over fused calcium chloride. Other zirconium carbodihydrazone complexes were prepared by similar procedures.

Preparation of oxovanadium( IV), cobalt( II), nickel( II) and copper( II) complexes

To a hot methanolic solution of carbohydrazones (0.01 mol) was added the respective metal acetylace­tonates (0.01 mol) dissolved in 20 mL of methanol. The reaction mixture was refluxed on a water bath for 4 h. To this, a few drops of I: I ammonia was added and mixture allowed to stand overnight. The precipi­tated complexes were suction filtered, washed with 5 mL of methanol and dried over fused calcium chlo­ride (yield 72%).

All the isolated products were purified by Soxhlet extraction using CH30H/ THF/CH2CI 2/DME solvents in which the metal complexes are insoluble or spar­ingly soluble whereas, the ligands are highly soluble in those solvents. The isolated complexes were fur­ther purified by repeated recrystallizations in CH30HffHF/CH2Ch/DME solvents until satisfactory melting points were obtained.

IR spectra of ligands and complexes in nujol mull

were recorded on Hitachi 270-50 spectrophotometer and the spectra calibrated relative to polystyrene film. Conductivity measurements were carried out on Elico model CM-180 digital conductivity bridge with cell of cell constant of l em·'. Magnetic susceptibility of the complexes were obtained at room temperature with Gouy balance, using Hg[Co(SCN)4] as calibrant. Electronic spectra of the isolated complexes were measured in DMF or DMSO on a Hitachi UV -vis spectrophotometer, model 200-20. 1H NNlR spectra were recorded on Varian-390, 200 MHz NMR spec­trometer operating in the Ff mode . Spectra were measured in d6-DMSO and CDCI3 with residual 1H resonance (2.40 ppm relative to TMS) or TMS as the internal standard.

The zirconium, vanadium, cobalt, nickel and cop­per contents in the metal complexes were determined by known methods. The analytical and magnetic data of isolated complexes are summarized in Table I .

The biological activity of ligands and metal com­plexes were studied by screening the isolated com­plexes against E. coli and S. aureus for antibacterial and against A. niger and C. albicans for antifungal behaviours. The microbial screenings were done by following in vitro cup diffusion method5

. The results

Table !-Characterization data of metal complexes

Sl. Empirical formula m.p. Found (Calcd), % llerr No. of complex oc M N BM

I Zr(C2sH26N407) 223-25 15.64 (15.51) 9.60 '(9.52) Diamagnetic 2 Zr(CnH3c~407) 230-33 14.92 (14.81) 9.16 (9 .10) Diamagnetic 3 Zr(C25H24N407Cl2) 240-43 13.98 ( 13.92) 8.58 (8.53) Diamagnetic 4 Zr(CnHJnN40~) 228-31 14.18 (14.11) 8.70 (8.58) Diamagnetic

5 YO(C 15Hc2N403) 231-35 14.04 (13.98) 15.42 (15.36) 1.89 6 YO(C17H,6N403) 238-40 13.04 ( 13.28) 14.38 (14.27) 1.93 7 YO(C, 5H wN403Cl2) 245-47 11.80 (11.7 1) 12.96 (12 .84) 1.79 8 YO(C 17H,6N40s) 229-32 12.05 (12.15) 13.23 (13.05) 1.74

9 Co(C 15H12N403) 210-12 16.60 ( 16.46) 15.77 (15.65) 2.04 10 Co(C 17H,6N403) 219-21 15.38 (15 .21) 14.62 (14.57) 2.29 II Co(C, 5H wN403Cl2) 240-43 13.90 (13.83) 13 .2-v (13.13) 2.15 t2 Co(C11H c6N40s) 220-24 14.20 (14.09) 13.23 (13 .17) 2.09

13 Ni(Cc5H12N403) 198-200 16.55 (16.47) 15.78 (15.47) Diamagne.tic 14 Ni(C11H c6N403) 205-07 15.33 ( 15 .28) 14.62 (14.51) Diamagnetic 15 Ni(C1sHwN403Cl2) 220-24 13.85 (13.72) 13.21 (13 .11) Diamagnetic 16 Ni(CI7HI6N40s) 216-18 14.15 (14.09) 13 .50 (13.41) Diamagnetic

17 Cu(C1sH 12N403) 231-33 17.66 (17.55) 15 .02 (14.91) t .87 18 Cu(C11H c6N403) 238-40 16.38 (16.28) 13.93 (13.61) 1.77 19 Cu(C 15H wN403CI2) 243-45 14.81 (14.73) 12.60 (12.56) 1.73 20 Cu(C 17H,6N40s) 230-33 15.13 (15.01) 12.87 ( 12.59) 1.93

W ARAD eta/.: METAL COMPLEXES OF CARBO HYDRAZIDE SCHIFF BASES . 417

from the biological studies are summarized m Table 2.

Results and Discussion The analytical data shown in Table 1 indicate that

all zirconium(IV), vanadium(IV), cobalt(II), nickel(II) and copper(II) metal ions form 1:1 (metal:ligand) complexes. The complexes are dark· yellow, light green, pink, dark green and light blue in colours re­spectively. All complexes are soluble in DMF, DMSO and pyridine and are sparingly soluble in 'al­cohol. The molar conductance data in DMF ( 1 o·3 mol) are too low to account for any dissociation of the complexes in DMF. Hence, the complexes can be re­garded as non-electrolytes in DMF.

Zirconium(IV) complexes with cf electronic con­figuration are expected to show diamagnetic behav­iour and this is evident from the observed diamag­netic behaviour of all the isolated zirconium com­plexes. The magnetic moments obtained for the oxo­vanadium(IV) complexes are in the range 1.79 to 1.94 BM, and these values are in the vicinity of spin only values of oxovanadium(IV) complexes hitherto re­ported. The results preclude the existence of ex­change interactions in these complexes. All cobalt(II) complexes show magnetic moments in the range 2.04 to 2.29 BM indicating that these complexes have low spin, square planar configuration. The square planar cobalt(II) complexes are reported to exhibit magnetic moments in the range 2.2 tq 2.7 BM.

Table 2-Bacterial and fungicidal activity of ligands and metal complexes

Sl R Cone. Bacterial Fungicidal no. mg E. coli S. aureus A. niger C. albicans

Ligands I H 100 14mm 13mm 15mm 14mm 2. 5-CH3 100 13 13 13 13 3. 5-CI 100 14 14 12 12 4. 3-0CH3 100 12 15 14 13

Zirconium complexes I H 100 14mm 13mm 15mm 14mm 2. 5-CH3 100 13 13 13 13 3. 5-CI 100 14 14 12 12 4. 3-0CH3 100 12 15 14 13

Vanadium complexes 5. H 100 09mm 08mm 12mm 13mm 6. 5-CH3 100 10 20 14 16 7. 5-CI 100 09 08 14 16 8. 3-0CH3 100 08 08 09 09

Cobalt complexes 9. H 100 08mm 08mm IOmm 09mm

10. 5-CH3 100 13 14 17 16 II. 5-CI 100 14 ' 12 08 09 12. 3-0CH3 100 10 10 10 II

Nickel complexes 13. H 100 14mm 16mm 14mm 15mm 14. S-CH3 100 09 10 II 12 15. 5-CI 100 09 10 10 10 16. 3-0CH3 100 12 13 13 12

Copper complexes 17. H 100 09mm 08mm 13mm 12mm .18. S-CH3 100 10 09 09 10 19. 5-CI 100 I I 12 12 09 20. 3-0CH3 100 10 09 09 09

Standard I. Gentamicin 100 20 20 2. Nystatin 100 20 20

Control DMSO 100 09 08 08 09

418 INDIAN J CHEM, SEC. A, APRIL 2000

All the nickel(II) complexes are found to be dia­magnetic in nature. This suggests that they may be having square planar geometry. The magnetic mo­ments observed for isolated copper(II) complexes fall in the range 1. 73 to 1.93 BM. These values suggest square planar geometry for these complexes with no major spin interactions.

All ligands exhibit broad band of medium intensity in the region 3250-3200 em·', that can be attributed to the VoHJNH vibrations.6 A medium to high intensity band observed in the region 1630-1610 em·' is attrib­uted to the Vc=N vibrations in view of the previous assignments.6 A group of three bands of medium in­tensity observed in the region 1580-1480 cm-1 is re­garded as due to the aromatic Vc=e vibrations. In ad­dition to these bands in the ligands, a high intensity band observed at 1270 em·' is attributed to the phe­nolic Vc.o vibrations7

• Assignments in these ligands have been made by comparing the spectra with those of model compounds such as benzylideneaniline and salicylideneanilines. The high intensity band appear-

ing in the region 1680-1670 em·' has been assigned to

the Vc=o vibrations. All complexes exhibit medium intensity bands in

the region 3250-3100 em·' that can be attributed to VNH vibrations. The high intensity band observed at 1270 em·' in the ligands attributed due to phenolic Vc.o. appears as a medium to high intensity band at 1310-1280 em·' in the spectra of complexes. These observations favour the formation of M-0 bond via deprotonation, and agree with the data reported by previous workers8

.

It has been reported in literature that in the schiff bases of salicylaldehyde, and orthohydroxyacetophe­none, phenolic Vc.o vibrations have been used as di­agnostic probe to know the formation of monodentate and oxygen bridged complexes. In the mononuclear complexes, wherein oxygen acts as a monodentate, the Vc.o at 1510 em·' (ref. 9) shifts to higher fre­quency by I 0- 15 em·' , whereas, in the bridging case, the shift is in the order of - 35 em·'. The carbodihy­drazones show medium intensity bands around 1510 cm·1 which are attributed to the phenolic Vc.o vibra­tions. In the corresponding metal complexes, this band is located at - 1530 em·' as medium intensity band and the observed shift are in the order 15-20 em_,_ Thi5 emphasizes that in these complexes, the phenolic oxygen is exhibiting a monodentate behaviour.

The band due to Vc=N in all the complexes appears

as a strong band in the region 1600 cm-1• The lower

frequency shift indicates the coordination of Vc=N group to metal through nitrogen. The Vc=o vibratif)n disappears completely in all the com]plexes. This may be interpreted as due to a large low1'!ring of C::O along with usual lowering of Vc=N group. However, the participation of ligand in its enol form without the participation of enolic oxygen in coordination cannot be ruled out. In addition to these frequencies, the complexes of zirconium(IV) show two bands in the region 1640-1650 ern·' in their infrared spectra which may be assigned to the Vc=o vi lbrations of the carbon­bonded acetylacetonate ligand which confirms the formation of mixed ligand _metal complexes 10 of the type Zr(acac),L. The assignment of ~he band to vari­ous VM-N, and VM-o vibrations in the lower region ap­pears to be complicated, as the ligand vibrati'ons in­terfere in this region . The assignments made here are, therefore, tentative and are mostly based on the pre­vious reports.

The VM-N vibrations assigned in the region 600-500-cm·' by the previous workers 1 1 !have shown to be inert to the metal ion. The metal sensitive vibrations are reported to occur in the lower region. For copper(II) and nickel(II) complexes with N and 0 donor ligands, these bands are assigned at 483 and 442 em·' respec­tively. These assignments are based on 14N and 15N isotopic studies. For nickel(II) complexes of tet­radentate schiff bases, the partially isotope sensitive bands at 533 and 488 em·' have been assigned to the vNi·N• associated with the ligand vibrations 12

. Based on these reports, medium to weak intensity bands in the region 585-440 cm-1 are assigned to VNi-N vibra­tions associated with the ligand modes. Similarly, the bands in the region 475-435 and 548-470 ern·' are assigned to Vco-N and Vcu-N vibrations respectively. It has been reported that metal sensitive YM-N vibrations occur at 230 em·' and in the region 560-470 crn- 1 in zirconium and oxovanadiurn complexes. Based on thi s, we have assigned the medium intensity band at 280 em·' to Vz.r.N vibrations and the medium to high intensity band found in the region 530-510 and 435-320 em·' for oxovanadium(IV) complexes.

Nakamoto and co-workers 13 have assigned the re­gion between 500 and 400 em·' for VM.o vibrations in the case of acetylacetonates of transi tion metals. Stud ies based on 180 isotope have pointed that for nickel(II) complexes of schiff bases, vM-o vibration appear at 323 and 294 em·'. For copper(II) ace-

W ARAD eta/.: METAL COMPLEXES OF CARBO HYDRAZIDE SCHIFF BASES 419

tylacetonates, two bands appearing at 455 and 295 cm·1 are assigned to Vcu-o vibrations. Similarly, we have assigned medium intensity bands in the region 320-300 cm·1 for VM-o vibrations for other metal com­plexes.

The electronic spectra of zirconium(N) complexes in DMF solution show two bands in the region centered at 22000-2300 and 28500-29585 cm·1. These bands are assigned to charge-transfer transitions respectively. The spectral data indicate zirconium is exhibiting higher coordination number, the spectral features resemble to those complexes with square antiprismatic configurations.

The electronic spectra of oxovanadium(N) com­plexes exhibit three bands in the region 22000-13000 cm·1. Several models . have been proposed in the lit­erature14 for the interpretation of the electronic spec­tra of oxovanadium(N) complexes . Among them, our results are consistent with Ballhausen and Gray model (BG model), since the difference between v1

and v2 bands is in the range 3150-3300 cm·1, which is less than 4000 cm·1, as expected for the model and hence assignments are made accordingly. The elec­tronic spectra of these complexes have identical fea­tures indicating similar geometries around vanadium atom. The isolated oxovanadium(N) complexes show all the expected three bands in the region 13000-13650, 16300-16800 and 21000-22000 cm·1. Of these, the first band reveals its identity as a broad band, whereas, second band occurs as a weak band. The third band, appearing at 21000 cm·1, may be due to the charge transfer transi tion between d 2 orbital of

z vanadium and 2px or 2py orbital of oxygen atom. The first and second bands are assigned to 2B2 ~

2E and 2B2 ~

2B1 transitions respectively. On the basis of available data, the complexes have been assigned the square pyrimidal structures.

All cobalt(II) complexes exhibit two bands in DMF in the region 15000-16500 cm·1 and another band of high intensity appears in the region 1.8000-22000 em -I. However, the relatively higher intensity of the second band leads to believe that the charge - transfer transitions also contribute to this part of the spectra. The first two bands are assigned to 2A18 ~

2B18 and 1A18 ~

2Eg transitions respectively, in view of the available reports on square planar cobalt(II) complexes 15'16.

All nickel(ll) complexes similarly exhibit two bands in DMF in the region 16200-17000 and a

second band in the region 18000-20000 cm-1. These bands may be attributed to 1A1g ~ 1

A2g and 1A2g ~ 1 B1g transitions respectively, as expected for square planar nickel(II) complexes. Further, a strong band observed at 28775 cm·1 is attributed to the charge -transfer band. On this basis, square planar configurations are suggested for all the isolated nickel(II) complexes.

The copper(II) complexes with carbohydrazones have shown two bands in the region 16000-17000 and 18000-20000 cm·1. These bands are well within the range expected for square planar copper(II) complexes. The square planar complexes can be distinguished from tetrahedral complexes. The tetrahedral complexes exhibit a narrow band below I 0000 cm·1. However, no such bands are observed in the present complexes. Hence tetrahedral or pseudo­tetrahedral geometry is ruled out17

• Meek and Ehrhardt18 have observed that square planar complexes have a complex broad band at relatively

higher frequencies (17000 cm-1). In the present complexes, three transitions 2B1g ~ 2

A 18 , 2B1g ~ 2B2g

and 2 B 18 ~ 2 Eg are observed in the region 16140 -

16500 , 18800 - 19500 cm·1 and 25000-30000 cm·1

respectively.

The molar extinction coefficient values of the electronic spectral bands measured in DMF, for all the complexes are generally found in the ranges 5-20 and 100-150 dm3 mor1 cm·1 for bands assigned to d-d and charge- transfer transitions respectively.

The 1H NMR spectrum of a representative ligand, bis(salicylaldehydo )-1 ,5-carbodihydrazone shows a resonance signal at about D 7.75 corresponding to the resonance absorption of the amide NH group. The observed signals at about D 8.4 correspond to the azomethine protons of =CH group and signals at D 10.8 corresponds to OH groups of the ligand. The multiplets centered at about D 6.9 and D 7.25 are at­tributed to aromatic protons. Other ligands show similar resonance signals in their 1H NMR spectra.

In the 1H NMR spectra of the metal complexes, azomethine =CH signals are shifted to downfield, as expected, and appears at about D 9.6. However, the resonance signals of the NH group does not appear to have been shifted significantly, whereas, the signals due to OH group of the ligands have diminished in metal complexes indicating deprotonation of ligands. The observed broad signals of vanadyl complexes confirm that they are paramagnetic in nature.

420 INDIAN J CHEM, SEC. A, APRIL 2000

~N~~ b~::·:··_·_-_ ... ___ -_~__ ~/~~:-~N

. ·--o~

0~~~ ~'o----------~------0 (I]

[II]

M=Co,Ni,

(III)

The magnetic measurements, infrared, electronic and 1H NMR spectral data have provided evidences for the structures of the isolated complexes. On the basis of these studies, probable structures for Zr, V, Co, Ni and Cu complexes have been proposed (structures I, II and III).

Biological studies The results from biological activity studies on the

isolated metal complexes are presented in Table 2. The general trends in their activities are summarized. It is evident from the data that among the zirconium, vanadium, nickel, cobalt and copper complexes un­substituted nickel complexes and 5-methyl substituted vanadium complexes exhibit high activity against E. coli and S. aureus among bacteria and A. niger and C.

. albicans among fungus. The remarkably high activity of 5-methyl of derivative of vanadium (entry number six in Table 2), towards S. aureus bacterial organisms is particularly significant. Vanadium compounds ex­hibiting such unusual biological activities, however,

are well-documented in the literatme19. Ali copper

complexes display moderate to weak activity against the above organisms. The 3-methoxy substituted co­balt complexes have shown good activity against E. coli organism. Remaining cobalt complexes substi­tuted with 3-methoxy, 5-chloro and un-substituted salicylaldehyde derivatives have shown weak activity against all the organisms.

Acknowledgement The authors are thankful to Prof. Y S Agasimundin,

Chairman, Dept. of Chemistry, Gulbarga University, for providing the laboratory facil ities and to the CSIR, New Delhi, for providing financial assistance and the award of a senior research fellowship to one of us (CDS) during the work.

References I. Kurzer F & Wilkinson M, Chem Rev, Ill (1970) and refer­

ences therein. 2 Chandra R, Acta chim Hung, 128 (1991 ) 73. 3 Maurya M R & Maurya R C, Rev inorg Chem, 15 (1995) I,

and references therein. 4 Fackler Jr J P, Prog inorg chem, 7 (1966) 361. 5 Indian pharmacopia, Government of India, New Delhi,

( 1985) Appendix 4, 90. 6 Biradar N S & Kulkarni V H, J inorg nucl Chem, 33 (1971)

2451. 7 Kovacic J E, Spectrochim Acta, 23A ( 1962) 183 . 8 Datta R L & Das B R, Indian J Chem, 22A (1983) 267. 9 Biradar N S & Havinale B R, lnorg chim Acta, 17 (1976)

157. I 0 Nakamoto K, Infrared spectra of inorganic and coordination

compounds 2nd Edn (Wiley, New York ) 1970, pp 247-256. II Sharma B L & Patel C C,lndian J Chem, 8 (1976) 747. 12 Glurchinsky P, Mockler G M & Sinn E, Spectrochim Acta,

33A ( 1972) I 073. 13 Chuke J B & Nakamoto K, lnorg Chem, 6 ( 1967) 433. 14 Selbin J, Chem Rev, 65 (1965) 153. & Coord chem Rev, I

(1966) 293. 15 Patil R B, J Indian chem Soc, 60 (1983) 218. 16 Atre V, Reddy G V, Sharada L N & Ganorkar M C, Indian J

Chem, 21A (1982) 935 . 17 Patil M S & Shah J R, J Indian chem Soc, 58 (1981) 944 &

60 (1983) 79. 18 Meek D W & Ehrhardt S A, lnorg Chem, 4 ( 1965) 584. 19 Rehder D, Angew Chem lnt Ed Engl. 30 (1991) 148 and

references therein.