The synthesis and characterization of a series of cobalt(III) complexes of the general type Co(N2O2)(L-2) are described. The N2O2 Schiff base ligands used are Me-salpn (H2Me-salpn = N,N'-bis(methylsalicylidene)-1,3-propylenediamine) (1-3) and Me-salbn (H2Me-salbn = N,N'-bis(methylsalicylidene)-1,4-butylenediamine) (4-5). The two ancillary ligands L include: pyridine (py) 1, 3-metheylpyridine (3-Mepy) 2, 1-methylimidazole (1-MeIm) 3, 4-methylpyridine (4-Mepy) 4 and pyridine (py) 5. These complexes have been characterized by elemental analyses, IR, UV-Vis, and H-1 NMR spectroscopy. The crystal structures of trans-[Co-III(Me-salpn)(py)(2)]PF6, 1, and cis-alpha-[Co-III(Me-salbn)(4-Mepy)(2)]BPh4 center dot 4-Mepy, 4, have been determined by X-ray diffraction. Examination of the solution and crystalline structures revealed that the outer coordination sphere of the complexes exerts a noticeable influence on the inner coordination sphere of the Co(III) ion. The electrochemical reduction of these complexes at a glassy carbon electrode in acetonitrile solution indicates that the first reduction process corresponding to Co-III-Co-II is electrochemically irreversible, which is accompanied by the dissociation of the axial (R-py)-cobalt bonds. It has also been observed that the Co(III) state is stabilized with increasing the flexibility of the ligand environment. (C) 2007 Elsevier Ltd. All rights reserved.
Paul Joseph Dyson, Farzaneh Fadaei Tirani, Mouna Hadiji