ABSTRACTThe geometries, relative energies and spectroscopic properties of α-isosaccharinate and D-gluconate complexes of uranyl(VI) are studied computationally using density functional theory. The effect of pH is accommodated by varying the number of water and hydroxide ligands accompanying gluconate in the equatorial plane of the uranyl unit. Their relative energies are found to be pH dependent, although the energetic differences between them are not sufficient to exclude the possibility of multiple speciation. The calculated uranyl stretching frequency decreases as pH increases, in agreement with previous experimental data. Three different coordination modes are studied.