A STUDY OF HYDRATED RARE-EARTH IONS

Hydrated lanthanide (III) ions Ln3+ (H2O)8 with Ln3+ = La3+ to Yb3+ have been studied using ab-initio methods. The binding energy as a function of ion-water distance and position of the ion in the rare earth series is discussed. The calculations are related to recent experimental results elucidating the hydration behaviour of lanthanide(III) ions. Since no S-shape behaviour is found for complex binding energies or metal-oxygen distance, the calculations indicate that observed thermo-dynamic anomalities should come from hydration number changes due to the different ionic radii within the series. The non-additivity of the ion-water interactions has been calculated and it is found that its relative importance increases from 26% for La3+ to 32% for Ln3+.