PHOTOCHEMISTRY OF THE MU-HYDROXO-MU-PEROXO-BIS[TRIETHYLENETETRAAMINE)COBALT(III)] COMPLEX IN BASIC AQUEOUS-SOLUTIONS

Photochemical reaction of the title complex [(trien)Co(mu-OH,O2)Co(trien]3+ (1) was studied in basic, aqueous solution. The photo-induced cobalt(II)-trien complexes, [Co(trien)(H2O)2]2+ and [Co(OH)(trien)(H2O)]+, react with dioxygen in oxygenated basic, aqueous solution to give the intermediates, [(OH)(trien)(Co-O2-Co(trien)(H2O)]3+ and [(OH)(trien)Co-O2-Co(trien)(OH)]2+, which are transformed reversibly into 1. The transient absorption spectra of the monobridged mu-peroxo complexes, which have an absorption maximum near 313 nm, were measured using a flash photolysis method. The rate constants of the reaction of cobalt(II)-trien complexes with dioxygen were measured as a function of pH. A small amount of [Co(trien)(H2O)2]3+ (2) was detected on prolonged irradiation in both the presence and absence of dioxygen. The photochemical reaction mechanisms are discussed, and the kinetic data of the reaction of cobalt(II)-trien complexes with dioxygen are compared with those obtained by a stopped-flow method.