Synthesis, Infrared Spectroscopic Characterization and Antimicrobial Studies of Co(III) Dimethylglyoximato Complexes with Aniline and Aniline-derived Axial Ligands

Abstract

Complexes with cobalt(III) have been used as models in the study of vitamin B12 chemistry. In this study, cobalt(III) complexes with dimethylglyoxime as equatorial ligand and aniline or substituted aniline as well as thiocyanate ion as axial ligands have been synthesized and characterized based on melting point, conductivity, solubility and infrared (IR) spectral studies. The complexes are formulated as [Co(Hdmg)2(B)(SCN)] where Hdmg is dimethylglyoximato, B = aniline (A), 4-bromoaline (4BrA), 2- nitroaniline (2NA), 4-nitroaniline (4NA) or 4-anisidine (4PA). The complexes were formed in low yields (33 – 37 %) except [Co(Hdmg)2(A)(SCN)] which was obtained in significant yield (65 %). The percentage yield of the synthesized cobaloximes follows the order A > 4NA > 4PA > 4BrA = 2NA. They are of various colours, soluble or slightly soluble in the solvents used and have melting points in the range (77 – 120 0C). The data from IR spectra indicated that the coordination compounds coordinated via the nitrogen of the ligands. Further supportive fact of the coordination of the ligands to the metal ions was deduced from the emergence of new bands due to v(M-N) in the metal complexes. In the proposed octahedral coordination sphere of the central cobalt atom, four coordination sites in the equatorial positions are occupied by nitrogen atoms of two dimethylglyoximate monoanions, and the other two sites are occupied by atoms of monodentate neutral ligands and thiocyanate anion. The measured molar conductance showed that the complexes are non-electrolytes, except [Co(Hdmg)2(4BrA)(SCN)] which has conductivity of 149 Scm2 mol-1, hence electrolytic in nature. The in vitro antibacterial potency of the complexes were assayed against some strains of bacteria such as MRSA (Methicillin Resistance Staphylococcus) Staphylococcus aureus, Bacillus subtilis, Streptococcus pneumoniae, and the Gram negative bacteria, Salmonella typhi, Klebsiella pneumoniae, Escherichia coli, and Pseudomonas aeruginosa. The results of the antimicrobial assay uncovered that the complexes have more potency than their free ligands but less than that of the standard drug (Gentamicin)