Biokemistri Nigerian Society for Experimental Biology ISSN: 0795-8080 Vol. 22, Num. 2, 2010, pp. 71-75

Biokemistri, Vol. 22, No. 2, Dec, 2010, pp. 71-75

Coordination Compounds of Co^II, Ni^II, Cu^II, Zn^II, Cd^II and Hg^II with Tridentate ONS Donor Azo dye Ligands.

Bipin B. Mahapatra* and Saroj Ku. Panda ^**

**P.G. Department of Chemistry, G.M. (Autonomous) College, Sambalpur – 768004 (Orissa). India Telephone No : -06632401177 E-mail: mahapatra.bipin@yahoo.com ^*, sarojbadmal@gmail.com ^**
**To whom correspondence should be addressed.

(Received September 7, 2010; Accepted December 10, 2010)

Code Number: bk10012

ABSTRACT

Twelve monomeric co–ordination compounds of Co^II , Ni^II, Cu^II, Zn^II, Cd^II and Hg^II with two ONS tridentate azodye ligands have been synthesized. The characterizations of these compounds have been made basing upon analytical conductance, magnetic susceptibility, I.R, electronic spectra, E.S.R. and N.M.R. spectral data. The Co^II and Ni^II complexes are found to be octahedral, Cu^II complexes are distorted octahedral and Zn^II, Cd^II and Hg^II complexes are found to be four co-ordinated possibly with tetrahedral geometry.

Key words: Azodye complexes, Co-ordination compounds, Metal complexes.

Introduction

The synthesis of co-ordination compounds using polydentate azodyes as ligands is of recent interest. Besides laboratory and industrial applications, the chemotherapeutic use¹ (Gaind et al, 1964) of azodyes has inspired the modern chemists to prepare new metal chelates by reacting with new polydentate azodyes with different transitional and non–transitional metal ions, in order to study their pharmacological properties. In continuation of our earlier work² (Mahapatra et al 2009), the present paper describes the preparation of two new oxygen, nitrogen and sulphur donor tridentate azodye ligands (Figs. 1 & 2) and their twelve monomeric co-ordination compounds.

All the chemicals were of B.D.H. or E. Merck grade. Metal, carbon, hydrogen, nitrogen and chlorine were estimated by standard methods³ (Vogel, 1969). Conductivity measurement in DMF was made using Toshniwal CL 01-06 Conductivity bridge. Magnetic moment was measured at RT by Gouy method. I.R. Spectra (KBr) were recorded on an IFS 66U Spectrophotometer, electronic spectra (10^-2M in acetone) using Hilger-Watt uvispeck spectrophotometer, N.M.R. spectra on a Jeol GSX 400 with acetoned6 as solvent and TMS as internal standard and ESR spectra on an E4-spectrometer.

Preparation of the ligand:

Conc. ammonium hydroxide (8.5 ml) was added slowly to distilled aniline (9.13 ml) at 0 – 5°C in an ice salt freezing mixture. Then distilled carbon disulphide (6.0 ml) was added drop wise with constant stirring for 1 hour with the help of a mechanical stirrer. The resulting white crystalline solid was obtained with decomposition temperature 33 -35°C. It was dried on exposure to air.

Preparation of o–hydroxy/o–carboxyphenylazophenyldithiocarbamate :-

To a cold solution of freshly prepared ammoniumphenyldithiocarbamate ( 9.3 gm in 100 ml), a cold aqueous solution of equimolecular amount of the diazonium chlorides obtained from O-aminophenol/Oaminobenzoic acid was added drop wise with stirring. The resulting solid compounds of reddish brown azodyes were obtained. These were then washed with distilled water, dried and crystallized from absolute ethanol.

Preparation of the complexes :-

The metal chlorides in ethanol were mixed separately with the ligands in dioxane in 1:1 molar ratio. The resulting solutions were heated to ~60 – 70⁰C for about 1 hour in a heating mantle. On cooling the P^H of the solutions were raised to ~7. The solid complexes thus separated were then washed with ethanol followed by ether and then dried in vacuum.

Results and Discussion

The co-ordination compounds synthesized have the compositions [M(L/L^I)Cl(H2O)2] , [M^I(L/L^I)Cl] where M=Co^II , Ni^II, Cu^II ; M^I =Zn^II,Cd^II, Hg^II; LH = o-carboxyphenylazophenyldithiocarbamate (C14H11N2O2S2) (Fig. 1) L^IH = o-hydroxyphenylazophenyldithiocarbamate. (C13H11N2OS2) (Fig. 2). All the complexes are either crystalline or amorphous in nature, and soluble in common organic solvents. The non-electrolyte nature of the complexes in DMF is shown from the low conductance values (4.2 – 5.6 Ω ^–1 cm² mol^-2). Both the ligands can be represented by two possible structure 3(a) and 3(b). In structure 3(a) the secondary nitrogen atom is bonded to the metal ions and in structure 3(b) the bonding of thione sulphur to the metal ions is observed.

Fig. 3

In the i.r. spectra of the ligands, the bands are obtained at 3298.9cm^-1 (LH) and 3206.5 cm^-1 (L^IH) which may be ascribed to intramolecular O–H…N hydrogen bonding. Disappearance of these bands in the metal chelates indicates the bonding of phenolic and carboxyl oxygen atoms to the metal ions. In the ligand (LH) νas (COO^-) and νs (COO^-) bands appear at 1633.8 cm^-1 and 1438.9 cm^-1 respectively and these bands appear in the metal chelates at ~ 1589.8 cm^-1 and ~ 1402.5 cm^-1 with a difference Δν of ~ 187.3 cm^-1 supporting monodentate nature of the carboxylate group⁴(Deccan & Philip 1980). The band at 1494.8 cm^-1 (L^IH) can be assign to phenolic C-O vibration and in the metal chelates this band appears at ~ 1467.7 cm^-1indicating the bonding of the ligand to the metal ions through phenolic oxygen atom⁵(Mishra & Keshri 1981).The sharp band observed at 1592.7 cm^-1 (LH) and 1592.9 cm^-1 (L^IH)can be attributed to ν (-N=N-) vibration and in the metal complexes these bands appear at ~ 1548.2 cm^-1 and ~ 1594.7cm^-1 respectively which indicates the bonding of one of the the azo nitrogen atoms to the metal ions ⁶(King R. B 1966). In the ligands sharp bands are observed at 1038.0 cm^-1 (LH) and 1070.9 cm^-1(L^IH) which can be attributed to ν ( C=S ) vibration and in the metal complexes this band is observed at 1019.4 cm^-1 and 1023.5 cm^-1 respectively which indicates the bonding of thiocarbonyl sulphur atom to the metal atoms⁷(Namakato & fujita 1963). in the metal chelates broad bands appear at ~ 3319.1-3550.9cm^-1 and ~ 840.2cm^-1 followed by sharp peaks at 730.1-725.4cm^-1 assignable to-OH stretching, rocking and wagging vibrations respectively indicating the presence of coordinated water molecules in the complexes⁸(Namakato 1963). The conclusive evidence of bonding of the ligands to the metal ions is proved by the appearance of bands at 515.8cm^-1-498.9 cm^-1assigned to (M–O) and 420.1–421.6 cm^-1 (M – N )⁹(Ferraro 1971).

In the electronic spectra of Ni^II complexes, four ligand field bands are observed at 10232(10256), 17552(17685) 25180(25250) and 32445(32525) cm^-1 assignable to³A2g(F) → ³T2g(F) (ν 1), → ³T1g(F) (ν 2), → ³T1g(P) (ν3) and CT transition respectively in an octahedral geometry. The ligand field parameters like Dq= 732.000(742.900)cm^-1,B = 802.400(811.133) cm^-1 , β35 = 0.826(0.835) cm^-1 , ν 2/ ν 1 = 1.715(1.724) and σ = 21.065% (19.760%) also support the octahedral symmetry for the complexes¹⁰(Sacconi 1968). In the electronic spectra of the Co^II complexes four ligand field bands are observed at 8250(8235), 16575(16510), 20342(20452) and 32150(32355) cm^-1. The first three bands can be attributed to ⁴T1g (F) → ⁴ T2g (F) (ν 1), → ⁴A2g (F) (ν 2) and → ⁴ T1g (P) (ν 3) transitions respectively and the fourth band is assigned to a CT band. The ligand field parameters like Dq=832.500(827.500) cm^-1,B = 811.133(817.133) cm^-1 , β35 = 0.835(0.841) cm^-1 , ν 2/ ν 1 = 2.009(2.005) and σ = 19.760 %( 18.906%) suggest an octahedral geometry for the complexes¹¹(Lever 1967). The electronic spectra of Cu^II complexes show one broad band at ~13375-14450 cm^-1 with maxima at ~14310 cm^-1 assignable to ²Eg�²T2g. transition in support of a distorted-octahedral configuration of the complexes¹²(Yamada 1966).

The ¹H NMR spectra of the ligands (LH) and (L^IH) were recorded in acetoned6. The complex pattern observed at δ 6.9300 –8.3028 (LH) and δ 6.9047 – 8.2739 (L^IH) corresponds to 09 phenyl protons each. The Co^II, Ni^II and Cu^II complexes exhibit magnetic moments at ~5.0, ~3.1 and ~1.8 B.M. indicating the presence of three, two and one unpaired electron respectively¹³(Cotton & Wilkinson, 1985).

The ‘g_av ’ values of the complexes [CuLCl(H₂ O)₂ ] and [CuL^ICl (H₂ O)₂] were found to be 2.0979 and 2.0441 respectively by Kneubuhl’s method¹⁴(Kneubuhl, 1966). This type of spectra may be due to dynamic or pseudo rotational behaviour of Jahn-Teller distortion. The covalent nature of the Cu–L band is indicated from low ‘gav’ value (< 2.3). This value is consistent with Cu–O and Cu–N bonded copper complexes. The Zn^II, Cd^II and Hg^II complexes are suggested to be four-coordinated probably with tetrahedral geometry basing upon analytical, conductance and i.r spectral data. Hence both the azodyes behave as tridentate ligands being bonded through azo nitrogen, phenolic or carboxylic oxygen and thione sulphur atoms.

Table 1

ACKNOWLEDGEMENT

The authors are thankful to the Head, SAIF, I.I.T. Madras for providing I.R., N.M.R. and E.S.R. spectral data.

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