Photochemistry of the μ-hydroxo-μ-peroxo- bis[triethylenetetraamine)cobalt(III)] complex in basic aqueous solutions

Abstract

Photochemical reaction of the title complex [(trien)Co(μ-OH,O 2)Co(trien) 3+ ( 1) was studied in basic, aqueous solution. The photo-induced cobalt(II)-trien complexes, [Co(trien)(H 2O) 2] 2+ and [Co(OH)(trien)(H 2O)] +, react with dioxygen in oxygenated basic, aqueous solution to give the intermediates, [(OH)(trien)Co-O 2-Co(trien)(H 2O)] 3+ and [(OH)(trien)Co-O 2-Co(trien)(OH)] 2+, which are transformed reversibly into 1. The transient absorption spectra of the monobridged μ-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)(H 2O) 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.