Synthesis, characterization and antimicrobial properties of Cobalt(III), Nickel(III), Copper(II) and Zinc(II) complexes with pyridine and thiocyanate

Mixed-ligand complexes of Co(III), Ni(III), Cu(II) and Zn(II) with pyridine and thiocyanate have been synthesized and characterized using elemental analysis, infrared and UV-Vis spectroscopy, thermal analytical techniques, melting point determination, molar conductivity and room temperature magnetic susceptibility measurements. The results suggest that all complexes are stable and molecular with octahedral coordination geometry for the Co(III) and Ni(III) complexes, square planar or tetrahedral geometry for the Cu(II) complex and a tetrahedral geometry for the Zn(II) complex. Evaluation of the antimicrobial activities of the ligands, metals salts and complexes on four bacterial strains (E. Coli, K.Pneumonia, S.typhi and S. flexneri) and four fungal strains (C. Albicans, C., Parapsilopsis, C. tropicalis and C. neoformans) showed higher activity of the complexes compared to the ligands and metals salts. The Co(III) complex showed higher activity than the reference drugs; doxycycline and Penicillin while the Cu(II) complex showed higher activity than the reference antibiotics; doxycycline and nystatin

Synthesis, Characterization, Cyclic Voltammetry, and Biological Studies of Co(II), Ni(II), and Cu(II) Complexes of a Tridentate Schiff Base, 1-((E)-(2-Mercaptophenylimino) Methyl) Naphthalen-2-ol (H2L1)

A novel tridentate Schiff base, 1-((E)-(2-mercaptophenylimino) methyl) naphthalen-2-ol (H2L1), was synthesized by the condensation reaction of 2-hydroxy-1-naphthaldehyde with 2-aminothiophenol in absolute ethanol. The resulting ligand was reacted with Co(II), Ni(II), and Cu(II) ions to obtain tetrahedral CoL1, NiL1, and square planar CuL1 complexes. The Schiff base and its metal complexes were characterized using 1H-NMR, microanalysis, FT-IR, UV-visible, and mass spectroscopy (ESI-MS). All the compounds are soluble in DMSO and DMF. Spectroscopic studies show that the ligand coordinates to the metal center through the azomethine nitrogen, naphthoxide oxygen, and thiophenoxide sulfur to form a tridentate chelate system. Conductance measurements show that these compounds are molecular in solution. Cyclic voltammetry studies show Co(III)/Co(II) and Cu(II)/Cu(I) redox systems to be quasi-reversible involving a monoelectronic transfer while Ni(III)/Ni(II) was irreversible. In vitro antibacterial and antifungal activity against five bacterial strains (Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Enterococcus faecalis, and Proteus mirabilis) and five fungal strains (Candida albicans, Candida glabrata, Candida tropicalis, Candida krusei, and Candida parapsilosis) showed no antifungal activity but moderate antibacterial activity on E. coli, S. aureus, P. aeruginosa, and P. mirabilis bacterial strains. Antioxidant studies reveal that the ligand and its Cu(II) complex are more potent than Co(II) and Ni(II) complexes to eliminate free radicals