The experimental data are analyzed in terms of a Born-Haber cycle as illustrated in Fig. . Assuming that all the gas states are well-approximated by the ideal gas, the sum of the solvation free energies of both solute ions is calculated from thermochemical tables to be -163.5 kcal/mol. Consequently our QCT calculation at the DFT level over-estimates the excess Gibbs binding free energy by roughly -15 kcal/mol.