The photochemical generation of superoxide Rh(iii) complexes

Abstract

The photolysis products of the [Rh(NH₃)₅(NO₂)](NO₃)₂ complex in aqueous solutions were studied by electron paramagnetic resonance (EPR), UV-visible (UV-vis), and ¹⁵N nuclear magnetic resonance (¹⁵N NMR) spectroscopies. Aqueous solutions of [Rh(NH₃)₅(NO₂)](NO₃)₂ became blue when exposed to UV irradiation under an oxygen-containing atmosphere while aqueous solutions of [Rh(NH₃)₅(NO₂)](NO₃)₂ with additives of NaNO₂ turned orange under the same conditions. Photolysis of degassed [Rh(NH₃)₅(NO₂)](NO₃)₂ solutions did not lead to any change of their color. It was suggested that, as a result of the photolysis, the complex decomposed with the formation of a NO₂ fragment and a fragment containing Rh(II). In the presence of molecular oxygen in solution, a superoxide complex, [Rh(NH₃)₅O₂]²⁺, was formed, in which electron transfer from the metal ion to O₂ took place.