Photochemistry of the cis- and trans-Dichlorobisethylenediamine Chromium(III) Cations in Acidic Aqueous Solutions. Observation of a Stereochemical Change in Photoaquation

Abstract

The photoreactions of cis- and trans-[CrCl2(en)2]+ have been investigated in acidic aqueous solution at pH 3 and 0 °C. On photolysis in the ligand field bands the cis isomer was found to undergo mainly ethylenediamine aquation, apparently to a thermally unstable monodentate protonated ethylenediamine complex, with a quantum yield of 0.13. In addition chloride aquation occurred with[Formula: see text]. In contrast, the trans isomer underwent exclusive chloride aquation with quantum yield 0.32. The results are qualitatively, but not quantitatively, in agreement with predictions of Adamson's empirical rules. It was found that for trans-[CrCl2(en)2]+ photolysis, the reaction product [CrCl(H2O)(en)2]2+ was produced at least 70% in the cis configuration.