Photosolvation of [Co(CN)6]3−, trans-[Cr(NH3)2(NCS)4]−, and trans-[Cr(en)2NCSF]+ in aqueous mixed solvent systems

Photosolvation of [Co(CN)6]3−(1), trans-[Cr(NH3)2(NCS)4]−(2) and trans-[Cr(en)2NCSF]+(3) has been studied in various water/methanol, ethanol, acetonitrile, ethylene glycol, glycerol, and acetone mixtures and in aqueous solutions of polyvinylpyrolidone. The quantum yield for thiocyanate loss from 3 was found to be fairly independent of solvent, while for thiocyanate loss from 2, large, and at higher concentrations of organic solvent, specific reductions of quantum yield were observed. The study of 1 using spectrophotometric analysis for [Co(CN)5H2O]2− yielded similar data to some in the literature, but the larger range of systems studied here did not support the reported reduction of quantum yield with bulk viscosity. Furthermore evidence from this and other work suggests that many of the observed quantum yield reductions are only apparent, based on a false assumption that the photosolvation is qualitatively the same in ail mixtures. The data are reinterpreted in terms of competitive solvation by both solvent components. It is argued that this study supports a dissociative model of reaction for 1, but an associative model for the chromium complexes 2 and 3.