SYNTHESIS, SPECTROSCOPIC CHARACTERIZATION, REDOX, AND BIOLOGICAL SCREENING STUDIES OF SOME SCHIFF BASE TRANSITION METAL(II) COMPLEXES DERIVED FROM SALICYLIDENE-4-AMINOANTIPYRINE AND 2-AMINOPHENOL/ 2-AMINOTHIOPHENOL

Abstract

Neutral complexes of Cu(II), Ni(II), Co(II), Mn(II), VO(IV) and Zn(II) have been synthesised from the Schiff bases derived from salicylidene-4-aminoantipyrine and 2-aminophenol/2-aminothiophenol. The structural features have been arrived at from their microanalytical, IR, UV-Vis., ¹H NMR and ESR spectral data. All of the complexes exhibit square-planar geometry except the Mn(II) and VO(IV) complexes. The Mn(II) chelates show an octahedral environment and the VO(IV) chelates exist in a square-pyramidal geometry. The non-electrolytic and monomeric nature of the complexes are evidenced by their magnetic susceptibility and low conductance data. The electrochemical behaviour of the Cu(II), Mn(II) and VO(IV) complexes in DMSO at 300 °K were studied. [CuL¹] complex shows an irreversible peak for the copper(II)/copper(I) couple at Ep_c1 = 0.16 V and Ep_a = 0.53V referenced to Ag/AgCl. The cyclic voltammogram of the [CuL²] complex in MeCN at 300°K shows a quasi-reversible peak for the couples copper(II)/copper(III) at Ep_c = 0.47 V and Ep_a = 0.61 V versus Ag/AgCl and two irreversible peaks for the copper(II) → copper(I) and copper(I) → copper(0) reduction at Ep_c = -0.63 V and -0.89 V, respectively. The [ MnL¹] complex shows two irreversible couples, manganese(II)/manganese(I) and manganese(I)/manganese(0) at Ep_c = -0.10 V and -0.84 V with the direct oxidation at Ep_a = -0.70 V and -0.04 V, respectively. X-band ESR spectra of the Cu(II) and VO(IV) complexes in DMSO at 300 and 77°K were recorded and their salient features are reported. The biological activities of the metal chelates against the bacteria Staphylococcus aureus, Bacillus subtilis, Klebsiella pneumoniae, Salmonella typhi, Pseudomonas aeruginosa and Shigella flexneri and the fungi Aspergillus nigerand Rhizoctonia bataicolaare also reported. Most of the complexes have higher activities than those of the free Schiff bases and the control.

ACKNOWLEDGMENTS

The authors express their sincere thanks to the University Grants Commission, New Delhi, for financial support and to Prof. P. R. Athappan, School of Chemistry, Madurai Kamaraj University, for CV facilities. The authors also thank the Managing Board, Principal and Head of the Department of Chemistry of Virudhunagar Hindu Nadars' Senthikumara Nadar College for providing research facilities. K. J. thanks the Management and Principal of Mepco Schlenk Engineering College for their support.