Synthesis, crystal structures, electrochemically studies and antibacterial properties of three new mono-nuclear and one very rare bi-nuclear cobalt(III) Schiff base complexes

Three new mononuclear and one new binuclear cobalt(III) complexes of tetradentate N2O2 donor Schiff base ligands [CoIII(L1)(3-Mepy)2]PF6 (1), [CoIII(L2)(3-Mepy)2]PF6 (2), [CoIII(L2)(4-Mepy)2]PF6 (3) and [CoIII2(L1)2(4-Mepy)4(PF6)4(K)2] (4) were synthesized by reaction of the resp. tetradentate ligands (L1 = bis(acetylacetone)ethylenediimine dianion, L2 = bis(benzoylacetone)ethylenediimine dianion) with the corresponding cobalt(II) salts in the presence of 3-Mepy and 4-Mepy. These complexes were characterized by FT-IR, 1H NMR and UV–Vis spectroscopy. The crystal structures of the complexes were determined by X-ray crystallography on solvated crystals. In dimeric cobalt(III) complex, two Co-Schiff base units were connected to two K(+) and four PF6 molecules to form the centrosymmetric, dimeric bi-nuclear complex, in which the Co(3+) cations showed distorted octahedral coordinations, while K(+) cations had different coordination numbers in two symmetry-independent moieties: in one of them it is 9-coordinated (irregular tricapped trigonal prism) and in the other 8-coordinated (distorted square prism). Biological activities of the complexes were studied on Staphylococcus aureus, Salmonella typhi, Escherichia coli, and Bacillus subtilis by the well diffusion method. The electrochemical behavior of these complexes with the goal of evaluating the structural effects on the redox properties was also studied.