COMPLEXES OF SCHIFF BASE DERIVED FROM ANTIPYRINE-4 CARBOXALDEHYDE AND METHYLAMINE (APAMA), {2 3-DIMETHYL-4-[(N METHYLIMINO)METHYL]

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1 CHAPTER V COBALT (II) COMPLEXES OF SCHIFF BASE DERIVED FROM ANTIPYRINE-4 CARBOXALDEHYDE AND METHYLAMINE (APAMA), {2 3-DIMETHYL-4-[(N METHYLIMINO)METHYL] l PHENYL-3-PYRAZOLIN-S-ONE} 5.1 Experimental Analysis Physical measurements 5.2 Results and discussion Electrical conductance Infrared spectra Electronic spectra Manetic behaviour 5.3 Coordination number and eometry

2 The importance of schiff base metal complexes and chelates servin as model systems of bioloical interest 1 16 has been discussed in Chapter I. Schiff bases have been b reputed for their ant1cancerous, ant1m1cro 1a,, ,, d 135 bacterostatlc, fun1statlc an tu berculostatic activities. The importance of schiff base in inhibitin the corrossion of mild steel in artifical sea water has also been reported. 223 Hence it was thouht worthwile to study a few complexes of the schiff base derived from an tipyrine-4- carboxaldehyde and methyl amine (APAMA). The present chapter is concerned with the preparation and characterisation of cobalt (II) complexes with APAMA havin counter anions chloride, bromide, nitrate and perchlorate. 5.1 Experimental The details reardin the preparation of the liand and purity of the reaents used are discussed in chapter II. The cobalt (II) chloride and bromide complexes were prepared by mixin the metal salt solutions (0.01 M) and APAMA solution (0.02M) in methanol. The nitrate and perchlorate complexes were prepared by mixin the metal and liand reaents in 1 :3 ratio, in methanol. The solution

3 mixture was refluxed for 2 to 3 hours and the resultin solution was concentrated. The solid complex formed was filtered, washed with petroleum ether and dried over phosphorous pentoxide in vacuum in a desciccator Analysis Cobalt in the complexes was estimated ravimetrically as pyridinethiocyanate after decomposin with sulphuric and perchloric acid. The chloride and bromide were estimated by Volhard's method and the perchlorate was estimated by Kurz's method. C, H, N were ana 1 yse d b y microanalytical methods Physical Measurements Molar conductances of the complexes 1n nitrobenzene, acetonitrile and methanol were measured on a direct readin conductivity meter. Infrared spectra of the liand and the complexes were recorded in the reion cm- 1 Manetic measurements were made by Gouy's method. Details of the physical measurements are iven in chapter II. 5.2 Results and Discussion The analytical data alon with the empirical formulae of the complexes are iven in Table 21.

4 80 Table 21 Elemental analysis data of Co(II) complexes of APAMA Metal% Anton% C% H % N% Complex Color Obs. Cal. Obs. Cal. Obs. Cal. Obs. Cal. Obs. Cal. C0Lp 2 Army Green Br 2 Army Green CoL 3 (NOJ 2 Brown-Red CoL 3 (Cl0 4 ) 2 Brown-Red Electrical Conductance The molar conductances of the complexes in nitrobenzene, acetonitrile and methanol usin approximately 10' 3 M solutions, determined at room temparature are iven in Table 22. Complex Table 22 Molar Conductance Values of Co(II) Complexes of APAMA Nature of t Concentration Nitro benzene Acetonitrile Methanol Electrolyte [ Cl 2 ] Non-conductor [Co1 2 Br 2 ] Non-conductor [CoL 3 ](N0 3 ) :2 [CoL 3 ](C 10 4 ) :2 * - ohm 1 cm 2 mol" 1

5 The molar conductance of 10-3 M solutions in nitrobenzene for 1: 1, 1 :2 and 1 :3 complexes are 20-30, and 70-80, and that in acetonitrite are , and ohm- 1 cm 2 mol- 1 respectively. In methanol, the conductance values rane from , , and for 1:1, 1:2 and 1:3 complexes for M solutions The conductance data reveal that chloride and bromide complexes are non-electrolytes. The nitrate and perchlorate complexes show 1 :2 electrolytic behaviour in all the solvents Infra red spectra The 1 R spectral bands of the liand and the complexes are iven in Table 23.

6 82 Table 23 R Spectral Bands of Co(II) Complexes of APA MA Liand Cl 2 Br 2 CoL)N0) 2 CoL 3 (Cl0 4 ) 2 Tentative Assinments 2935W 2930W 2932W 2932W 2930W varyl C-H 2820s 2810s 2815s 2805s 2805s vc-h of N-CH s 1635s 1635s 1630vs 1630vs vc= s 1580s 1580s 1560s 1565s vc= N 1490m 1495m 1495m 1493m 1490m Rin stretechin of pyrazolone and phenyl ri n s 1440m 1440m 1440m 1432m 1430m VCH m 1430m 1425m 1420m 1420m asy C-Hdef Pyrazolone rin stretchin 1380s --- V 3 ionic NO,i m 1345m 1320m 1320m 1320m 1325m 1320m vc-n vibration 1265s 1260s 1260m 1258m 1260m N-phenyl stretchin 1205w 195w 1175w 1172w 1170w 1170w 1172w vc-n 1150m 1130m s v 3 C w 1100m 1110m 1100m 1100m vc-n 1020m 1020m 1020m 1025m 1025m Benzene rin breathin 925w 925w 925w 925w 920w Benzene rin breathin 905w 905w 905w 900w 900w 860w 860w 850w 850w 860w Ysym. C-C m --- V 2 N0 3 - ionic 780w 780w 780w 780w 780w C-H substituted II 765w 760w 765w 760w 760w v 4 Cl m 615m 615m 610m C-0 in plane bendin m 590m

7 83 A stron band at 1646cm- 1 for APAMA is assinable to the C = 0 stretchin frequency of the pyrazo 1 one rin., This band is shifted to a lower frequency in all the complexes, indicatin that coordination occurs throuh oxyen atom of the pyrazolone rin. Another stron band at 1590 cm- 1 for the liand is assined to the C = N vibration. The C = N stretchin expected around 1650cm- 1 is shifted from its normal value. The lowerin has been attributed to factors as conjuation, and couplin with C = C This band also ets shifted to a lower frequency in all the complexes, indicative of the coordination throuh azomethine nitroen atom. Thus APAMA acts as a bidendate liand in the complexes. The cobalt (II) chloride and bromide complexes show a shift of C = 0 frequency from 1646 cm 1 to 1635 cm-1, while the nitrate and perchlorate complexes show a shift to 1630 cm 1 The C = N stretchin frequency at 1590 cm- 1 is lowered to 1580 cm 1 for the chloride and bromide complexes, whereas it ets shifted to 1560 and 1565 cm- 1 for the nitrate and perchlorate complexes. The data show the coordination of the azomethine nitroen in the complexes. In the nitrate complex, the bands at 1380, 825 and 730 cm- 1 respectively of v3, v2 and v4 of nitrate roup suest ionic nature for the

8 nitrate. The conductance data also support this observation. The perchlorate complex shows bands at 1110 cm- 1 (v3) and 625 cm- 1 (v ). 4 The unsplit nature of these bands shows that the perchlorate retains tetrahedral symmetry and consequently its ionic nature in the complex. This is in conformity with the conductance data also Electronic Spectra The electronic spectral behaviour of co halt (II) h ave b een d. 1scusse d 1n. Ch apter III Th e e 1 ectron1c spectral data of the cobalt (II) complexes are iven in Table 24. The electronic spectra of all the complexes under investiation suest octahedral confiuration. All the complexes show a broad band around 19,000 cm- 1 which can be assined to 4 T 1 (F) 4 T 1 (P) transition of octahedral cobalt (II). 231 In addition to this, the chloride complex shows a band at 20,833 cm-1, bromide at 23,800 cm-1, nitrate at 21,739 cm- 1 and perchlorate at 22,220 cm 1, all assinable to chare transfer process.

9 85 Table 24 Electronic Spectral data of Co(II) complexes of APAMA in methanol Complex Absorption Maximum Amax (nm) v(cm 1) Cl Br [CoL 3 ](N0 3 ) [CoL 3 ](Cl0 4 ) Assinments Chare Tran sf er 4T I (F) ---) 4 T I (F) Chare Tran sf er 4T i (F) ---) 4T i (F) Chare Tran sf er 4T i (F) ---) 4 T i (P) Chare Transfer 4T I (F) ---) 4T 1 (P) Manetic Behaviour The effective manetic moments of the cobalt (II) complexes are iven in Table 25. Table 25 Manetic Suscepeticbilities and Manetic Moments of Cobalt (11) complexes of APAMA Name of XX 106 xd x 106 the complex es units e. sunits Cl Br CoL 3 (NOJ CoL 3 (ClO 4 ) xm = Molar susceptibility xd = diamanetic susceptibility xm = Corrected molar susceptibility µerr= Effective Manetic moment xm' X 106 C..s. units µerr(bm)

10 The eneral manetic behaviour of cobalt (II). 1 d. d comp exes 1s 1scusse 1n Ch apter III. Th e manetic moments of the complexes under investiation rane from 4.8 to 5. lbm, which are characterestic of octahedral confiuration. The electronic spectral data aree with this inference Coordination number and eometry Cobalt (II) complexes of APAMA havin counter anions chloride, bromide, nitrate and perchlorate were synthesised. The complexes have the empirical formulae Cl 2, Br 2, CoL 3 (N0) 2 and CoL 3 (ClO 4 ) 2 where L = liand. The molar conductance values of M solutions of the complexes in nitrobenzene, acetonitrile and methanol show that the chloride and bromide complexes are nonelectrolytes whereas the nitrate and perchlorate complexes are 1 :2 electrolytes. The 1 R spectral data are indicative of the bidendate nature of APAMA. The coordination occurs throuh the oxyen atom of the pyrazolone rin and the nitroen atom of the azomethine roup. The nitrate complex shows v 3, v 2 and v 4 bands at 1380, 825 and 730 cm- 1, indicatin the ionic nature. The unsplit bands at 1110 (v) and 625 cm-1 (v4 ) suest the non-coordinated, ionic nature

11 of perchlorate in the perchlorate complex. The electronic spectra of all the complexes show bands around 19,000 cm- 1 assinable for 4 T 1 (F) --) 4 T 1 (P) transition, characterstic of octahedral cobalt (II). All the complexes show chare transfer bands above 21,000 cm- 1 The manetic data also support the octahedral confiuration of the complexes. All the complexes have manetic moments in the rane 4.8 to 5.1 BM. 87