PHOTOLYSIS OF COBALT(III) CHELATES WITH CON4O2, CON3O3 AND CON2O4 CHROMOPHORES

Ultraviolet irradiation of the complexes trans-[Co(N2O2)(N-ax)(2)](+) and cis-beta-[Co(N2O2)(acac)] in methanol (where N2O2 = open-chain quadridentate Schiff base dianionic ligands of acacen, salen or benacen-type; N-ax = N-donor axial ligands NH3 or pyridine; acac = 2,4-pentadionate anion) gives rise to photosubstitution of one axial ligand (in trans-complexes) forming trans-[Co(N2O2)(N-ax)(CH3OH)](+), and photoreduction of Co(III) to Co(II) (in cis-beta-complexes), respectively. The complexes trans-[Co(N2O2)(py)(CH3OH)](+) are are photochemically stable at 313 nm irradiation, they undergo, however, the photoreduction of Co(Ill) to Co(II) coupled to the oxidation of methanol to formaldehyde at 254 nm irradiation. The efficiency of both the heterolytic and homolytic breaking of a bond between the central atom Co(III) and a monodentate or the bidentate ligand is influenced by the peripheral groups of the quadridentate N2O2-ligands. The electronic properties of these groups (expressed by means of their Hammett parameters) do not correlate with the quantum yields of the photochemical reactions.