A study of lanthanide(III) (hydroxy)carboxylate complexes in aqueous medium using lanthanide induced oxygen‐17 NMR shifts

Abstract

Abstract The complexation of dysprosium(III), as the model cation for calcium(II), with a series of (hydroxy)carboxylates in aqueous medium, has been studied by 17 O NMR spectroscopy. Acetate, 3‐hydroxybutyrate, glycolate, lactate, malonate, malate and citrate show fast ligand exchange on the 17 O NMR time scale at 73°. The Dy(III)‐induced 17 O shifts of both the ligand and the water, which are mainly due to contact interaction, provide valuable information on the complexation sites of the ligands as well as on the number of coordinated waters in the complexes. The results point to a rather constant 17 O contact shift upon the formation of Dy(III)‐O bonds. On the other hand, oxydiacetate (ODA), (carboxymethoxy)succinate (CMOS) and nitrilotriacetate (NTA) show slow ligand exchange on the 17 O NMR time scale at 73°. In these cases the Dy(III)‐induced shift of the 17 O water resonance provides information on the stoichiometry of the complexes, i.e. the number of coordinated waters and the number of ligands.