Solvation and complexation of copper (II) and chloride ions in 2,2,2-trifluoroethanol–dimethyl sulphoxide mixtures

Abstract

The formation of copper(II) chloro-complexes has been studied by calorimetry and spectrophotometry in various 2,2,2-trifluoroethanol (TFE)–dimethyl sulphoxide (DMSO) mixtures at 25 °C. It was shown that as the mole fraction of TFE, x, in the mixtures increased, the formation constant of [CuCl]⁺ gradually decreased to x= 0.8. The result is contrary to that obtained for acetonitrile (AN)–DMSO mixtures. This is ascribed to the decreased entropy of formation of [CuCl]⁺ in TFE–DMSO mixtures in contrast to the increased entropy in AN–DMSO mixtures with decreasing DMSO content. The corresponding enthalpy of formation of [CuCl]⁺ remains practically unchanged over the wide range of solvent composition in TFE–DMSO mixtures, as well as in AN–DMSO mixtures. The different variation trend in the entropy of formation of [CuCl]⁺ in TFE–DMSO and AN–DMSO mixtures may be explained in terms of the different intermolecular interactions between solvent molecules in the bulk.