Interactions of zinc(II), magnesium(II) and calcium(II) with aminomethane-1,1-diphosphonic acids in aqueous solutions

Abstract

Complex formation equilibria of the aminomethane-1,1-diphosphonic acids with Zn II, Mg II and Ca II have been studied by potentiometric pH titrations and by means of NMR spectroscopy. The ligands exhibit a strong tendency to form protonated species over a wide range of pH. The most efficient binding mode in all the studied systems is the formation of the six-membered chelate ring involving oxygens of both phosphonate groups. An evident preference for the formation of multinuclear complexes is noted in the case of zinc(II). Magnesium demonstrates preference for mononuclear complexes, whereas calcium(II) tends to form insoluble species with most of the studied ligands. The structures of the main complex species are discussed with respect to the priorities in the hydrogen-bond network organization in solid state.