Photolysis of Ammine and Alkylamine Chromium(III) Complexes in Water and Dimethylsulfoxide: Mechanistic Evidence from Luminescence and Medium Effects

Abstract

Photosolvolysis of [Formula: see text] Cr(NH3)5Cl2+, Cr(CH3NH2)5Cl2+, and Cr(CH3CH2NH2)5Cl2+ in water and DMSO is described. Phosphorescence of [Formula: see text] is completely quenched in base but loss of NH3 is not. This implies that photosolvolysis arises in the quartet excited state and not the phosphorescent doublet. The increase in ammine quantum yield in DMSO as compared to water can be understood in terms of a tetragonal distortion model for the quartet which also accommodates phosphorescence activation energy data. Unfavorable solvation of Cl− of Cr(RNH2)5Cl2+ (R = H, CH3, CH3CH2) after tetragonal distortion can also explain the reversal of solvent effect in these systems wherein quantum yields are lower in DMSO than in water for both release of RNH2 and Cl−.