Ionic partial molar heat capacities in non-aqueous solvents

Standard partial molar constant pressure heat capacity data at 298 K for 8 tetra-alkyl or -aryl ions and 10 smaller ions in 10 solvents, including water, have been statistically related to diverse ion and solvent properties. For the large ions linear relationships are obtained between C_{p CA} ^∞ (CA is a 1:1 electrolyte) and the number n_C of carbon atoms in the alkyl chains: one for water, one for alcohols, and one for aprotic solvents. The dependences of C_{p i} ^∞ (i is an ion) on properties of the ions and solvents can be grouped for various kinds of small ions and solvents: for all ions in the aprotic solvents and for cations and anions separately in the protic ones. The relevant ion properties are in all cases the charge, z_i, the reciprocal of the radius, 1/r_i, and the polarizability, α_i. The statistically important solvent properties are the isothermal compressibility, κ_s, the solubility parameter, δ_s, and the Kamlet-Taft hydrogen bond donation, α_s, and acceptance, β_s, abilities. An attempt is made to rationalize these findings.