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 nC 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, zi, the reciprocal of the radius, 1/ri, and the polarizability, αi. The statistically important solvent properties are the isothermal compressibility, κs, the solubility parameter, δs, and the Kamlet–Taft hydrogen bond donation, αs, and acceptance, βs, abilities. An attempt is made to rationalize these findings.