Analytical Sciences

Three Empirical Correlations Connecting Gaseous Cluster Energies and Solvation Energies of Alkali Metal and Halide Ions

Jirí RAIS* and Tatsuhiro OKADA**

*Nuclear Research Institute plc Rez, 25068 Rez, Czech Republic
**National Institute of Advanced Industrial Science and Technology, Higashi 1-1-1, Central 5, Tsukuba, Ibaraki 305-8565, Japan

This paper gives two empirical correlations of formation Gibbs energies of gaseous clusters ΔG^f_n as function of number of solvent molecules attached to the ion, n, and one correlation connecting the ΔG^f_n for each individual cluster with the total ΔG^o_hydr value. The experimental ratios of ΔG^f₂/ΔG^f₁ and ΔG^f₃/ΔG^f₁ for both alkali metal and halide ions are on average equal to 0.75 and 0.5, respectively. ΔG^f_n values for n ≥ 4 are correlated with n as ΔG^f_n = [a/(n - 1)] ΔG^f₁ + b ΔG^f₁. For all available data on cluster energies and each individual cluster, the ΔG^f_n's are straight-line functions of ΔG^o_hydr. This well corresponds to another empirical rule stating that the Gibbs energies of transfer of ions between two solvents are often as well straight-line functions of ΔG^o_hydr [J. Rais and T. Okada, J. Phys. Chem. A, 2000, 104, 7314]. Tentative models of the found behavior are proposed. A full data set of the gaseous cluster energies of formation based on inclusion of new, usually not used entries from the literature is provided.

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