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Formation of mono- and binuclear neodymium(iii)-gluconate complexes in aqueous solutions in the pH range of 2-8.
Title Formation of mono- and binuclear neodymium(iii)-gluconate complexes in aqueous solutions in the pH range of 2-8.
Authors Kutus, B.; Varga, N.; Peintler, G.; Lupan, A.; Attia, A.A.A.; Pálinkó, I.; Sipos, P.
Journal Dalton Trans
DOI 10.1039/c7dt00909g
Abstract

The complex formation between Nd(iii) and d-gluconate (Gluc(-)) is of relevance in modelling the chemical equilibria of radioactive waste repositories. In the present work, the formation of NdpGlucqH-r complexes at 25 °C and pH = 2-8 was studied via spectrophotometry, potentiometry, freezing point depression, conductometry and NMR spectroscopy. In addition to the four mononuclear complexes (pq-r = 110, 120, 130 and 11-2), the formation of two binuclear, so far unknown complexes (pq-r = 23-2 and 24-2) was revealed. Between pH = 5.5 and 7, with the increasing metal ion and ligand concentrations, the Nd2Gluc3H-2(+) species becomes progressively predominant. Under the conditions characteristic of waste repositories, however, the formation of these complexes can be neglected. Regarding the binding sites of Gluc(-), C2-OH and C3-OH groups, in addition to the carboxylate ion, were identified from (1)H and (13)C spectroscopic measurements. Above pH = 6, the metal-ligand interactions became stronger implying the formation of deprotonated complexes involving the C2-OH group, while the displacement of the second proton at the C3-OH is also possible. The metal ion induced deprotonation of the ligand was confirmed by DFT calculations.