Synthesis, characterization and spectroscopic and electrochemical studies of new axially coordinated cobalt(III) salen (salen = N,N′-bis(salicylidene)-1,2-ethylenediamine) complexes.: The crystal structure of [CoIII(salen)(aniline)2]ClO4

Cobalt(III) complexes with some salen ligands (salen = N,N'-bis(salicylidene)-1,2-ethylenediamine) as equatorial and potentially tetradentate ligands and with different axial amine ligands (cyclohexylamine, aniline, 4-picoline and pyridine) were synthesized in situ and characterized by IR, H-1 NMR and elemental analysis. Electronic spectra and electrochemical properties of the complexes were studied in DNIF solutions. Electronic structure calculations indicate that the absorption between 420 and 440 nm, which are the lowest energy transfers in the complexes, are attributed to metal-ligand charge transfer transitions. The cyclic voltammetry of the complexes show an irreversible reduction of Co(III) to Co(II) and a reversible reduction of Co(II) to Co(I). The axial ligands affect reduction potentials of Co(III) in the order of changes of axial ligands' pK(a). The crystal structure of [Co(salen)(aniline)(2)]ClO4 was determined. In the [Co(salen)(aniline)(2)]ClO4, cobalt(III) center is six coordinated surrounded by an equatorial tetradentate salen Schiff-base ligand and two aniline axial ligands and ClO4- acts as a counter ion. (c) 2005 Elsevier Ltd. All rights reserved.