Photothermal studies of the photodegradation of (μ-peroxo)(μ-hydroxo)bis[bis(bipyridyl)Co(III)] and (μ-peroxo)(μ-hydroxo)bis[bis(phenanthroline)Co(III)] complexes in water

Abstract

We report here thermodynamic parameters associated with the photodegradation of water soluble (μ-peroxo)(μ-hydroxo)bis[bis(bipyridyl)Co(III)] and (μ-peroxo)(μ-hydroxo)bis[bis(phenanthroline)Co(III)] complexes. Photolysis of these complexes results in the release of dioxygen and the formation of the (H 2O) 4·(L) 2Co(II) complex where L=bipyridyl or phenanthroline. Photoacoustic calorimetry data reveals an enthalpy for photolysis of 71 kcal mol −1 with a corresponding molar volume change of +39 ml mol −1 for the bipyridine complex. For the corresponding phenanthroline complex an enthalpy change of 68 kcal mol −1 and molar volume change of +19 ml mol −1 are observed. These values are considered as a sum of the intrinsic volume changes due to the bond cleavage and bond formation and the volume change due to electrostriction. The larger volume change for the (μ-peroxo)(μ-hydroxo)bis[bis(bipyridyl)Co(III)] complex is attributed to a spin-state change of the Co ion upon photolysis which is not present in the (μ-peroxo)(μ-hydroxo)bis[bis(phenanthroline)Co(III)] photoproduct.