Contribution of non coulombic forces to ion-pair formation in some non-aqueous polar solvents

Abstract

Ion-pair formation of alkali and tetra-alkylammonium salts in propanol, acetonitrile and propylene carbonate has been investigated with the help of precise conductivity measurements in dilute solutions (10^–4 < c < 10^–2) in the temperature range from –45 to +25°C.¹ The temperature dependence of the association constant, K_A, yields the thermodynamic data ΔG⁰_A, ΔH⁰_A and ΔS⁰_A which are divided into a coulombic ion–ion and a residual term. Contributions from ion-solvent interaction depend on the nature of the solvent and the electrolyte compound. The distances of closest approach of the ions in the ion-pairs are compared with crystallographic radii (alkali salts) or radii deduced from the ionic size (tetra-alkylammonium salts).