Thermodynamic and Multinuclear NMR Study of Beryllium(II) Hydrolysis and Beryllium(II) Complex Formation with Oxalate, Malonate, and Succinate Anions in Aqueous Solution

Abstract

The hydrolysis of beryllium(II) and its complexation by oxalate, malonate, and succinate in 0.5 mol dm−3 NaClO4 aqueous solution at 298 K has been studied by means of potentiometric (pH-metric), microcalorimetric, and multinuclear NMR-spectroscopic measurements. The protonation properties of the three ligands have also been investigated by potentiometry and microcalorimetry under the same experimental conditions. Thermodynamic results are consistent with a previously proposed chemical model for beryllium(II) hydrolysis, involving the species [Be2OH]3+, [Be3(OH)3]3+, [Be5(OH)6]4+, [Be6(OH)8]4+, and Be(OH)2. Complex formation of beryllium(II) with the dicarboxylate ligands is invariably promoted by favourable entropic contributions (ΔS° > 0), while the enthalpic terms are always unfavourable (ΔH° > 0). Malonate forms by far the most stable complexes owing to a more favourable (less endothermic) enthalpic contribution. These data reflect the fitting of the “bites” of the ligands with the stereochemically required tetrahedral coordination geometry about the metal ion, as well as the ligand preorganization.