Co(III) complexes of Me-salpn and Me-salbn and the ring size effect on the coordination modes and electrochemical properties: The crystal structures of trans-[Co-III(Me-salpn)(py)(2)]PF6 and cis-alpha-[Co-III(Me-salbn)(4-Mepy)(2)]BPh4 center dot 4-Mepy

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.