Cluster-Continuum Model as a Sanity Check of Sodium Ions? Gibbs Free Energies of Transfer

An approach to estimate the uncertainty of the calculated through the monomer cycle cluster-continuum model Gibbs free energy of transfer has been developed and suggested to be used as a quantitative measure of the reliability of the predictions. A set of experimental Na+ free energies of transfer from water to 18 solvents (Delta Gtr(Na+, W -> S)) has been assessed. For all solvents, we find Na+(S)n clusters to be thermodynamically unstable if n > 5. For 1,2dichloroethane (1,2-DCIE), we have resolved considerable (ca. 10 kcal mol-1) discrepancies between available experimental Delta Gtr(Na+, W -> S). For 1,1-DCIE, we reject the only available experimental value and recommend our own estimate instead. We strongly propose experimental revisiting of Delta Gtr(Na+, W -> S) for ethylene glycol and hexamethylphosphoramide. The statistical analysis performed on a set of predicted and recommended experimental Delta Gtr(Na+, W -> S) values, in this work, results in the mean unsigned and signed deviations of 3.4 and -1.3 kcal mol-1, respectively. The squared Pearson correlation coefficient of 0.91 encourages the extension of the utilized theoretical approach to other available experimental data on ion solvation.

Automated summary

An approach to estimate the uncertainty of calculated Gibbs free energy of transfer has been developed and suggested as a measure of reliability. The Na+ free energies of transfer from water to 18 solvents have been assessed, revealing thermodynamic instability for Na+(S)n clusters in certain solvents. Discrepancies in experimental values for certain compounds were resolved and a statistical analysis showed good correlation and deviation with recommended values.