SYNTHESIS, SPECTRAL, REDOX, AND ANTIMICROBIAL ACTIVITY OF SCHIFF BASE TRANSITION METAL(II) COMPLEXES DERIVED FROM 4-AMINOANTIPYRINE AND BENZIL

Abstract

ABSTRACT A novel quadridentate, N2O2-type Schiff base, synthesised from 1-phenyl-2,3-dimethyl-4-aminopyrazol-5-one (4-aminoantipyrine) and benzil, forms stable complexes with transition metal ions such as Cu(II), Ni(II), Co(II), Mn(II), Zn(II) and VO(IV) in ethanol. Microanalytical data, magnetic susceptibility, IR, UV-Vis., 1H NMR, ESR and mass spectral techniques were used to confirm the structures. Electronic absorption and IR spectra of the complexes suggest an octahedral geometry around the central metal ion, except for the VO(IV)complex which has a square pyramidal geometry. The non-electrolytic behaviour of the chelates was assessed from the low conductance data, except for the vanadyl complex and the dipyridinyl adducts of the copper complexes which show a higher conductance, supporting an electrolytic nature of these complexes. The monomeric nature of the chelates was confirmed by their magnetic susceptibility values. Cyclic voltammograms of the [CuLCl2] and [CuL(OAc)2] complexes in DMSO solution at 300 K show a quasi-reversible peak for the Cu(II)/Cu(I) couple at Epa=−0.02 V and 0.54 V and Epc=−0.28 V and 0.23 V, respectively. The peak potentials were found to be solvent-dependent. The cyclic voltammogram of the[VOL]SO4 complex in MeCN shows a quasi-reversible peak for the VO(IV)/VO(V) couple and another peak characteristic for the VO(IV)/VO(III) couple. The X-band ESR spectra of copper, manganese and vanadyl complexes in DMSO solution were recorded and their M.O. coefficients were also calculated. The in vitro antimicrobial activity of the investigated compounds and uncomplexed metal salts were tested against bacteria such as Staphylococcus aureus, Bacillus subtilis, Klebsiella pneumoniae, Salmonella typhi, Pseudomonous aeruginosa, Shigella flexneri and fungi such as Aspergillus niger and Rhizoctonia bataicola. Most of the metal chelates show higher antimicrobial activity for the above microorganisms than the free ligand and lower activity than the uncomplexed metal salts.