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.
