Complexation of Lanthanide(III) Ions with Polyhydroxy Carboxylic Acids in Aqueous Solutions

Abstract

The complexation of lanthanum(III), europium(III), dysprosium(III), erbium(III), and lutetium(III) with D-gluconic acid (LH) was studied by pH potentiometry and NMR. The set of complexes formed in aqueous solutions and their stability constants β were determined, and the results were compared to those previously found for praseodymium(III) (S. Giroux et al., Polyhedron 2000, 19, 1567). A regular evolution of the β values was observed along the lanthanide series, particularly for the neutral complex MLH−2 (where two hydroxy functions were deprotonated) with a selectivity similar to that of EDTA. For the ML2+ complex, where the ligand was coordinated via the carboxylate groups, the analysis of the 13C NMR pseudo-contact shift showed that the carboxylate group was not bidentate and that there was a participation of the α-hydroxy group in the coordination. The study of the complexation of PrIII with other hydroxy carboxylic acids: glyceric, threonic, 2-hydroxybutanoic, and 3-hydroxybutanoic acids confirms that in the complex MLH−2 the deprotonated hydroxy groups, that intervene in the coordination with the metal ion, are those in α and γ positions relative to the carboxylate group. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)