Trimeric uranyl(vi)–citrate forms Na+, Ca2+, and La3+ sandwich complexes in aqueous solution

Abstract

M. Basile, et al., Chem. Commun., 2015, 51, 5306–5309, showed that a sodium ion is sandwiched by uranyl(VI) oxygen atoms of two 3 : 3 uranyl(VI)–citrate complex molecules in single-crystals. By means of NMR spectroscopy supported by DFT calculations we provide unambiguous evidence for this complex to persist in aqueous solution above a critical concentration of 3 mM uranyl citrate. Unprecedented Ca²⁺ and La³⁺ coordination by a bis-(η³-uranyl(VI)-oxo) motif advances the understanding of uranium's aqueous chemistry. As determined from ¹⁷O NMR, Ca²⁺ and more distinctly La³⁺ cause strong OUO polarization, which opens up new ways for uranyl(VI)-oxygen activation and functionalization.