Liquid-liquid partition and aqueous phase hydration of beryllium β-diketonates

Abstract

Partition coefficients of four beryllium β-diketonates of two homologous series in aqueous NaClO4 solution/n-hexane systems have been measured as functions of temperature (5–45°C) and of sodium perchlorate concentration (0–3 M). The ligands examined were: acetylacetone, propionylacetone, 3-methylacetylacetone, and 3-ethylacetylacetone. ΔG°, ΔH°, ΔS°, and ΔC°p2 values for the partition processes have been evaluated as well as salting-out coefficients of the chelates and the corresponding ΔH° and ΔS° values. The results have been interpreted in terms of water structure changes (hydrophobic hydration) and of specific hydration in the outer coordination sphere of the coordinatively saturated chelates (hydration of the bonded ligands). The effect of changing both number and position of the CH2 groups in the ligand molecules on ΔG°p can be described using the surface area approach to the hydrophobic interaction. Irregularities in the remaining thermodynamic quantities indicate, however, a possibility of changes in the outer-sphere hydration of the chelates, probably due to the inductive effect of the ligand substituents. A contribution from the outer-sphere hydration must not be neglected when analysing thermodynamics of extraction of metal complexes.