Thermodynamic study on the transfer of the tin(II), lead(II) and alkaline-earth-metal ions from water to methanol, dimethyl sulfoxide, acetonitrile, pyridine and N,N-dimethylthioformamide

Abstract

The thermodynamic functions for the transfer reactions of the tin(II), lead(II) and alkaline-earth-metal ions from water to methanol, acetonitrile, dimethyl sulfoxide and pyridine, and of the tin(II) and lead(II) ions to N,N-dimethylthioformamide, are reported. The Gibbs energies of transfer, Δ_tG^⊖, have been calculated from the standard electrode potentials of the Sn²⁺/Sn(s) and Pb²⁺/Pb(s) couples, which have been determined potentiometrically with the Ag(s)/Ag⁺ electrode as reference in the title solvents, and the Gibbs energies of transfer of the silver ion. The Gibbs energies of transfer of the alkaline-earth-metal ions were calculated from electrode or halfwave potentials of the M²⁺/M(am) couples in the title solvents and the difference in standard electrode potential between the M²⁺/M(am) and M²⁺/M(s) couples reported in the literature. The enthalpies of transfer, Δ_tH^⊖, have been obtained from calorimetrically determined enthalpies of solution of the anhydrous metal trifluoromethylsulfonates. The entropies of transfer, Δ_tS^⊖, have been calculated from the experimentally determined Δ_tG^⊖ and Δ_tH^⊖ values. All measurements have been carried out at 25 °C. The extrathermodynamic tetraphenylarsonium tetraphenylborate (TATB) assumption has been applied in order to calculate the contributions from the single ions. The tin(II) and lead(II) ions are solvated more strongly in dimethyl sulfoxide and N,N-dimethylthioformamide than in water, while they are solvated more weakly in methanol and acetonitrile. The small tin(II) ion is solvated more weakly and the larger lead(II) ion is solvated more strongly in pyridine than in water. The alkaline-earth-metal ions are solvated more strongly in dimethyl sulfoxide than in water, while methanol and the nitrogen donor solvents acetonitrile and pyridine solvate these ions more weakly than water. The enthalpies of transfer for these ions to the solvents studied are exothermic except for the tin(II), calcium and strontium ions to acetonitrile. The entropies of transfer to all solvents are markedly negative except for N,N-dimethylthioformamide where the TΔ_tS^⊖ values are close to zero. The difference in solvation of an ion between two solvents is mainly dependent on the bonding character of the ion–solvate bonds and on the way in which the ion affects the solvent bulk.