Photochemistry of μ-Amido-μ-hyperoxo-dicobalt(III) Complexes with Ammine and Polyamine Ligands in Aqueous Solutions: Effects of Ligand and pH

Abstract Photolyses of μ-amido-μ-hyperoxo-dicobalt(III) complexes, [LCo(NH2,O2−)CoL]4+ (L = 4NH3 (1), en + 2NH3 (2), 2en (3), tren (4)), (tren: 2,2′,2″-triaminotriethylamine, en: ethylenediamine) were investigated. The photolysis of complex 4 in a neutral aqueous solution produced a μ-hydroxo-μ-peroxo-dicobalt(III) complex, [(tren)Co(OH,O22−)Co(tren)]3+, together with a mononuclear cobalt(III) complex, [Co(NH3)(tren)(H2O)]3+. A mononuclear complex and Co2+ were produced in the photolyses of μ-hyperoxo complexes 1 and 2 containing NH3 ligand in neutral aqueous solutions. In acidic media, only mononuclear complex and Co2+ were produced in the photolysis of all μ-hyperoxo complexes examined. Quantum yields of the complexes with NH3 increased with increasing the number of coordinated NH3 (φ = 0.25, 0.11, 0.023, and 0.028 for complexes 1, 2, 3, and 4, respectively, at 365 nm irradiation in neutral region). The quantum yields obtained in acidic solutions were similar in magnitude to those obtained in neutral solutions.