Synthesis, characterization and pulse radiolysis of cobalt(II) complexes of 2-picolinate and polypyridyl ligands

Complexes of the type [Co(pic)(2)(LL)], where pic = picolinate; LL = (H(2)O)(2) (1), 2,2'-bipyridine (bpy) (2), 1,10-phenanthroline (phen) (3) and dipyrido[3,2-a:2',3'-c]phenazine (dppz) (4) have been synthesized and characterized by elemental analysis, IR, UV-visible and (1)H-NMR spectroscopy. Complex 2 crystallized from a mixture of chloroform and methanol in orthorhombic crystal system, space group Iba2. Complex 3 crystallizes from chloroform in monoclinic crystal system, space group P12(1)/al and in a mixture of water and methanol in triclinic crystal system, space group P (1) over bar. Co(II)/Co(III) oxidation potentials have been determined by cyclic voltammetry and the concomitant spectral changes measured by spectroelectrochemistry. The reactions of one electron reducing (e(aq)(-), (CH(3))(2)(center dot)COH and CO(2)(center dot-)) and one electron oxidizing ((center dot)OH) radicals with the above metal complexes have been studied by pulse radiolysis. The rate constants for the reaction of e(aq)(-) and SOH radicals with the complexes are of the order of 10(10) and 10(9) dm(3) mol(-1) s(-1), respectively. The reaction of hydrated electron (e(aq)(-)) with the complexes results in the formation of a ligand radical anion species which decays by either protonation of ligand or reduction of metal by intramolecular electron transfer resulting in cobalt(I) species. The reaction of (center dot)OH radical forms the OH-adducts of the ligand.