Transfer thermodynamic study on the copper(II) ion from water to methanol, acetonitrile, dimethyl sulfoxide and pyridine

Abstract

The thermodynamic functions for the transfer reaction of the copper(II) ion from water to methanol, acetonitrile, dimethyl sulfoxide and pyridine are reported. The extrathermodynamic tetraphenylarsonium tetraphenylborate assumption has been applied in order to calculate the contribution from the individual ions. The Gibbs energies of transfer, Δ_tG^⊖, have been calculated from potentiometrically determined standard electrode potentials. The enthalpies of transfer, Δ_tH^⊖, have been obtained from calorimetrically determined enthalpies of solution, Δ_solH^⊖, of anhydrous copper(II) trifluoromethylsulfonate. The entropies of transfer, Δ_tS^⊖, were calculated from the experimentally determined Δ_tG^⊖ and Δ_tH^⊖ values. All data refer to 25 °C. The copper(II) ion, which is regarded as a borderline acceptor, is strongly solvated by dimethyl sulfoxide, pyridine and liquid ammonia, but it is weakly solvated by methanol and acetonitrile. The solvation pattern of the copper(I) ion is significantly different from that of the copper(II) ion. The copper(I) ion, a soft electron-pair acceptor, is most strongly solvated by acetonitrile and the soft donor solvents pyridine, tetrahydrothiophene and liquid ammonia.