Hydration thermodynamics of plutonium and transplutonium ions

Abstract

Since thermodynamic properties are related to crystallographic radii, we first present sets of precise values of crystallographic radii (R) for ionic charge +2, +3 and +4 and different coordination numbers (CN). These data are based on the values reported by Shannon as well as variations of R with CN as observed for lanthanides, and linear correlations between isoelectronic M m+ and N n+ ions. Accurate measurements of the volume of the unit cell of oxides, fluorides and chlorides carried out recently give reliable radii values. Experimental entropies of actinide aquo ions are limited to Pu 3+ and Th 4+. Since this property depends on the structure of the hydrated ion, we decompose ionic entropies into three terms, related to electronic configuration, mass of the central ion, and structure of the aquo ion (S h). We use our data on the structure of trivalent actinide ions to derive S h and therefore to estimate values of trivalent ionic entropies. Entropies of divalent and tetravalent ions are also obtained similarly. Finally, taking into account the structure of the aqueous actinide ions, we calculate hydration enthalpies of +2, +3 and +4 actinide ions.