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 Epc1 = 0.16 V and Epa = 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 Epc = 0.47 V and Epa = 0.61 V versus Ag/AgCl and two irreversible peaks for the copper(II) → copper(I) and copper(I) → copper(0) reduction at Epc = -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 Epc = -0.10 V and -0.84 V with the direct oxidation at Epa = -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.