Synthesis, crystal structures, spectroscopic studies and antibacterial properties of a series of mononuclear cobalt(III) Schiff base complexes

New complexes of cobalt(III) with the tridentate and tetradentate Schiff base ligands: 3-methoxy-2-{(Z)[(2-hydroxyphenyl)imino]methyl}phenol (H2L1), 4-[(2-hydroxyphenyl)imino]-2-pentanone (H2L2); and 2-((E)-1-(2-((E)-1-(2-hydroxy-4,5-dimethylphenyl)ethylideneamino)ethylimino)ethyl)-4,5 dimethylphenol (H2L3), namely [CoIII(L1)(N-MeIm)3]PF6 (1), [CoIII(L1)(py)3]ClO4 (2), [Co(L1)(py)3][Co(L1)2] (3) and [CoIII(L2)(N-MeIm)3]PF6 (4) and [Co(L3)(N-MeIm)2]PF6 (5), were synthesized and characterized by physico-chemical and spectroscopic methods. The crystal structures of the complexes were determined by X-ray crystallography. In each of these complexes, the cobalt(III) centre has a slightly distorted octahedral environment, utilizing all available coordination centres of the ligands. The complexes were also screened for in vitro antibacterial activities against four human pathogenic bacteria, and their minimum inhibitory concentrations indicated good antibacterial activities.