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 O[double bond, length as m-dash]U[double bond, length as m-dash]O polarization, which opens up new ways for uranyl(vi)-oxygen activation and functionalization.