Inorganica Chimica Acta, 127 (1987) 25- 34 Determination of Heats and Entropies of Transfer for some Univalent Ions from Water to Methanol, Acetonitrile, Dimethylsulfoxide, Pyridine and Tetrahydrothiophene MATS JOHNSSON and INGMAR PERSSON Inorganic Chemistry 1, Chemical Center, University of Lund, P.O. Box 124, S-221 00 Lund, Sweden (Received August 14, 1986) 25 Abstract The heats of solution, AH:, for a large number of 1: 1 salts have been determined in water, methanol, acetonitrile, dimethylsulfoxide, pyridine and tetra- hydrothiophene. The heats of transfer, AH&, from water to the other solvents for 2 1 univalent ions have been calculated from the heats of solution deter- mined in this study and values taken from the literature. The extrathermodynamic tetraphenyl- arsonium tetraphenylborate assumption, stating that, A&(AsPh4+) = A&(BPh4-) for all pairs of solvents, have been applied to calculate the A/$ values for single ions. The entropies of transfer, A&,, of single ions have been calculated from Gibbs free energies and heats of transfer. The solvents used in this study represent a wide range of donor properties. Water and methanol are hard oxygen donor solvents, which solvate hard acceptors fairly well and soft acceptors poorly. Dimethylsulfoxide is, for the studied acceptors, an oxygen donor solvent. It solvates hard acceptors very well and soft acceptors fairly well. Pyridine, a nitrogen donor, and tetra- hydrothiophene, a sulfur donor, are typical soft donor solvents, solvating soft acceptors very well and hard acceptors poorly. Acetonitrile shows a specific solvation of univalent d” acceptors, while it solvates other acceptors fairly poorly. The halides are more weakly solvated in aprotic solvents because these are not able to form hydrogen bonds. In spite of stronger solvation of several ions in water, the heats of transfer to other solvents are generally negative. The negative as,“, values arise from the difference in bulk order between water which is well-ordered through hydro- gen bonding, and the less ordered aprotic solvents. Introduction As part of transfer thermodynamic studies, the heats of transfer from water (W) to methanol (M), acetonitrile (AN), dimethylsulfoxide (DMSO), pyridine (Py) and tetrahydrothiophene (THT) for 21 univalent ions are reported in this paper, including 0020-1693/87/$3.50 those taken from the literature [ 11. The choice of solvents has been discussed in a previous paper, also reporting the Gibbs free energy of transfer, AC:, for the same ions and solvents [2]. The tetraphenyl- arsonium tetraphenylborate (TATB) assumption [3, 41 has been applied as the necessary extrathermo- dynamic assumption in this study. The strength of the solvation depends on the kind of interaction which is formed between the ion and the solvent molecules. Solvation through van der Waals interactions is always present in condensed phases, but it is dominating only in a very limited number of solvents, e.g. alkanes, alkenes and benzene [5]. The energy gained through van der Waals solvation of ionic compounds is never large enough on its own to exceed the lattice energies. Ionic com- pounds can therefore not be dissolved in this kind of solvent. Solvents with one or several donor atoms are in most cases able to form interactions with ions of varying character. The degree of electrostatic and covalent contribution varies widely between different kinds of solvents. Hard acceptors are most strongly solvated in solvents able to form strong electrostatic interactions with ions. Oxygen and nitrogen donor solvents, in general, solvate hard acceptors well, while solvents with polarizable donor atoms such as phos- phorous and sulfur solvate hard acceptors poorly [ 1, 2, 61. Soft acceptors form the strongest solvates with solvents able to develop strong covalent bonds, e.g. phosphorous and sulfur donor solvents [6]. Among the nitrogen donor solvents, liquid ammonia, amines and pyridine solvate soft acceptors well, while nitriles solvate these acceptors, except for the univalent d” acceptors, poorly [6]. Oxygen donors, in general, solvate soft acceptors poorly [6]. Anions are solvated through the electrostatic forces formed between the ion and the solvent mole- cule dipoles surrounding it. The donor properties of a solvent are of no importance since anions are donors themselves. Anions prone to form hydrogen bonds are especially well solvated in protic solvents; thus the halides are more strongly solvated in protic than in aprotic solvents [2,7]. 0 Elsevier Sequoia/Printed in Switzerland