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

Kretzschmar, J.; Tsushima, S.; Drobot, B.; Steudtner, R.; Schmeide, K.; Stumpf, T.

Basile et al. (Chem. Commun., 2015, 51, 5306–5309) showed that a sodium ion is sandwiched by the uranyl(VI) oxygen atoms of two 3:3 uranyl(VI)–citrate complex molecules in single-crystals. By means of NMR spectroscopy supported by DFT calculation 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 especially La3+ cause strong O=U=O polarization which opens up new ways for uranyl(VI)-oxygen activation and functionalization.

Keywords: uranium; uranyl; U(VI); citric acid; NMR; DFT; spectroscopy; molecular structure

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Publ.-Id: 31389