Complexation of uranyl(vi) with succinimidedioxime in comparison with glutarimidedioxime

Abstract

Succinimidedioxime (H₃^sA) and glutarimidedioxime (H₃^gA) are two homologous compounds that represent one of the functional groups of amidoxime adsorbents for extracting uranium from seawater. These small imidedioximes can be conveniently prepared by the reactions of the relevant di-nitriles with hydroxylamine at elevated temperatures. The complexation of uranyl(VI) with H₃^sA is thermodynamically and structurally studied with potentiometric titration, IR spectroscopy, and computation in comparison with H₃^gA. With similar protonation properties, the interactions between uranyl(VI) and the two ligands are quite different in terms of coordination modes and strength. For complex species of the same stoichiometries formed at low pH, the stability constants of H₃^sA with uranyl complexes are significantly smaller than those of H₃^gA. Simulation in seawater environment shows that H₃^sA can compete with carbonate, but it is a weaker ligand than H₃^gA for binding uranyl(VI). In near-neutral solutions both ligands form insoluble uranyl complexes but with different stoichiometries and coordination modes, which are identified through composition analyses and DFT calculations. Different from H₃^gA, in favor of the 1 : 2 uranyl(VI) complex species, H₃^sA tends to form a cross-linked 2 : 2 binuclear complex with uranyl. These results help understanding the interaction mechanism between the functional groups of amidoxime polymer materials and uranyl ions in seawater.