Synthesis, crystal structures and electrochemical properties of CoIII complexes with hexadentate ligand containing thioether-amidopyridyl donor set

Two new cobalt(III) complexes of the hexadentate ligand [1,4-bis[o-(pyridine-2-carboxamidophenyl)]-1,4-dithiobutane] (H(2)bpctb) with N4S2 donor set atoms have been synthesized. A reaction of Co(CH3COO)(2)center dot 4H(2)O with (H(2)bpctb) leads to the formation of [Co-III(bpctb)]PF6 (1) having a CoN2(pyridine)N'(2)(amide)S-2(thioether) coordination by symmetric bpctb(2-) ligand. A similar reaction under slightly different conditions, however, gives [Co-III(L (a) )(L (b) )] (2), resulting from a C-S bond cleavage reaction triggered by an acetate ion as a base, having CoN2(pyridine)N'(2)(amide)S(thioether)S'(thiolate) coordination. These two Co(III) complexes have been characterized by elemental analyses and spectroscopic methods, and the crystal and molecular structures of [Co-III(bpctb)]PF6 (1) in the form of the solvate (1 center dot MeOH center dot H2O) and of [Co-III(L (a) )(L (b) )] (2) have been determined by X-ray crystallography. The Co atoms of both complexes exhibit distorted octahedral geometry. The electrochemical investigation of [Co(bpctb)]PF6 center dot MeOH center dot H2O (1 center dot MeOH center dot H2O) and [Co-III(L (a) )(L (b) )] (2) by cyclic voltammetry reveals a reversible Co-III-Co-II redox process at E (1/2) = -0.32 V (Delta E (p) = 80 mV); for 1, and E (1/2) = -0. 87 V (Delta E (p) = 70 mV) for 2.