The photolysis reactions of the complex ions [Cr(en)2ox]+ and [Cren(ox)2]− have been studied in the pH range 1 → 3 and at temperatures from 0 to 25 °C. It has been found that both ions photoaquate to a monodentate protonated ethylenediamine complex which then undergoes further aquation thermally with loss of the ethylenediamine ligand. Quantum yields for these aquations were measured for irradiation into the ligand field bands, the values obtained being 0.18 and 0.02, respectively. The results are discussed in terms of known empirical correlations for Cr(III) complexes. Assuming these reactions may occur from the 4T2g state as precursor, arguments are presented that the correlation between quantum yield and ΔE may depend on mixing of the 4T2g and 2Eg states, and its effect on the intersystem crossing rate constant.
