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

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.