Formation of mono- and binuclear complexes of Nd3+ with d-gluconate ions in hyperalkaline solutions – Composition, equilibria and structure

Abstract

The composition and stability constants (or formation constants) of complexes comprising of d-gluconate (Gluc–) and Nd3+ has been determined via potentiometry and Vis-spectrophotometry in aqueous solutions at 4.0 M (NaCl) ionic strength and in alkaline conditions. The chemical model derived from these measurements were complemented with freezing-point depression, Raman, ESI-MS and 1H/13C NMR measurements, some of these contributed to reveal structural features of the complexes formed. The presence of four variously protonated binuclear (Nd2Gluc4H–53–, Nd2Gluc4H–64–, Nd2Gluc6H–44–, Nd2Gluc6H–55–) and a mononuclear (NdGluc2H–54–) complexes were detected in highly alkaline media. The main coordination sites are the carboxylate and the alcoholate group attached to the C2 and C3 carbon atoms. The chemical picture obtained from our studies is of potential relevance in modeling some aspects of the aqueous chemistry of low or intermediate level radioactive waste (L/ILW) repositories.