Thermodynamics and structures in solvents coordinating through nitrogen. I. Enthalpies of transfer from water to pyridine and acetonitrile for some monovalent cations and anions

Abstract

The enthalpies of transfer ΔH_trº, between water and the aprotic solvents pyridine and acetonitrile have been determined for a number of 1-1 electrolytes. To calculate ΔH_trº for the single ions, the tatb assumption that ΔH_trº,(Ph₄As+) = ΔH_trºBPh₄-) for all solvents has been applied. The results are compared with those found earlier for the transfer between water and dimethyl sulfoxide. The values of ΔH_trº, differ widely between different ions, from exothermic by c. 30 kJ/mol to endothermic by about the same amount. Endothermic values are found for Cl^- and, though much smaller, for Br^-, and also for the large tetraalkylammonium ion Bu₄N⁺. Compared to the differences in ΔH_trº, found between the various ions, the differences found for a certain ion between different solvents are small. The decrease of AH,", in the sequence Cl^- > Br^- > I^- runs almost parallel in the three aprotic solvents, and is much less steep than in water. This reflects the influence of ligand hydrogen bonding in the protic solvent.