In the first part, a series of the cobalt(III) complexes of the general type trans- [Co(N 2 O 2 )(L 2 )]X have been synthesized and characterized by elemental analyses, IR, UV–Vis, and 1 H–NMR spectroscopy. The N 2 O 2 is dianionic tetradentate Schiff base ligand occuping the equatorial sites, and L = benzylamine (bzlan) 1 , piperidine (pprdn) 2 , morpholine (mrpln) 3 , pyrrolidine (prldn) 4 , 3-methylpyridine (3-Mepy) 5 , 4-methylpyridine (4-Mepy) 6 , pyridine (py) 7 , and 1-methylimidazole (1-MeIm) 8 . The structures of ( 1 ) and ( 5 ) have been determined by X-ray diffraction. While the Co(N 2 O 2 ) unit in 1 adopts a stepped non-planar conformation, an umbrella conformation is assumed by the Co(Me-salen) unit in complex 5 . The electrochemical reduction of these complexes at a glassy carbon electrode in acetonitrile solution indicates that the first reduction potential of Co(III/II) is irreversible, which is accompanied by the dissociation of the axial (amine)–cobalt bonds. The electron affinity of these complexes increases with increasing pK b of the axial ligand. The second reduction potential of Co(II/I) shows reversible behavior and is independent of the pK b of the axial ligand, which indicates loss of the axial amine and the involvement of a four coordinate speciese in this process. In the second part, a series of cobalt(III) complexes with thioamide ligands have been synthesized and characterized by elemental analyses, IR, UV–Vis, and 1 H–NMR spectroscopy and the structures of ( 9 ), ( 10 ), ( 11 ) and( 12 ) have been determined by X-ray diffraction. the molecular structures of these complexes show that the thioamide ligands are S-bonded and occupy the axial positions. The coordination geometry around the Co(III) center in these complexes is a distorted octahedron . The compounds exhibit a long wavelength LLCT, mediated by the metal center. The observed solvatochromism is explained by the effect that solvents of low dielectric constant have on the LLCT. In the last part, coper(II) complex [Cu((BA) 2 pn)] ( 13 ) and cobalt(III) complex trans -[Co(salophen)(py) 2 ]ClO 4 ( 14 ) have been synthesized and characterized by elemental analyses and X-ray diffraction. Complex ( 13 ) is a mononuclear copper(II) complex. . In complex ( 14 ), the coordination polyhedron is approximately octahedral, but the point group Cs furnishes an even better description.