Cobalt(II) and nickel(II) complexes of thiomethylated anilines: Characterization and in-vitro antimicrobial studies

Abstract

The cobalt(II) (1A-6A) and nickel(II) (1B-6B) complexes of the thiomethylated anilines substituted with -H (1), -CH3 (2), -OCH3 (3), -Cl (4), -Br (5) and –NO2 (6) were synthesized and characterized by elemental analyses, FTIR, UV-Vis spectra and conductance measurements. The experimental elemental analyses of the compounds were in agreement with calculated values, resulting to [ML2Cl2] (M = Co, Ni) stoichiometries of the complexes. Infrared spectra showed the bidentate ligands were coordinated to the metal ions through the nitrogen and sulphur atoms. The electronic spectra of the ligands exhibited ???* and n??* transitions in the ranges 262–271 nm and 298–315 nm, which were shifted to the longer wavelengths of 265–278 nm and 302–328 nm in the metal complexes respectively. The d?d bands in the visible region of the spectra suggested octahedral geometries for these complexes. The conductance values of the metal complexes in DMF in the ranges 28.6–35.8 and 68.1–74.3 ?–1 cm2 mol–1 indicated their behavior as nonelectrolytes (cobalt(II)) and 1:1 electrolytes (nickel(II)). The compounds were evaluated for in-vitro antimicrobial activity against S. aureus, B. subtilis, E. coli and C. albicans using the agar disc diffusion technique. The Gram-positive bacteria were more susceptible to the test compounds than the Gram-negative bacterium and the fungus. The cobalt(II) complexes demonstrated better inhibitory activity (8–14 mm) against the microbial organisms compared to the parent ligands (7–13 mm) and the nickel(II) complexes (8–10 mm).