Ionic solvation in water + cosolvent mixtures. Part 10.—Free energies of transfer of single ions from water into water + ethanonitrile mixtures

Abstract

The spectrophotometric solvent-sorting method using trace additions of 4-nitroaniline to determine the free energy of transfer of the proton between water and water + cosolvent has been applied to aqueous mixtures containing ethanonitrile. These experimental values for ΔG°_t(H⁺) are then used to calculate values for ΔG°_t(X^–) from values for ΔG°_t(HX), and these values for ΔG°_t(X^–) are in turn used to calculate values for ΔG°_t(M^m+) from values for ΔG°_t(MX_m). These values for ΔG°_t for individual ions are compared with similar values for aqueous mixtures containing other cosolvents: in general, ΔG°_t(Ph₄As⁺)≠ΔG°_t(BPh^–₄). A comparison of these overall values for ΔG°_t(i) deriving from structural changes throughout the solution with values for free energies of transfer deriving from structural changes in the inner coordination shell illustrates the importance of such structural changes outside the first coordination sphere.