The relationship of monodentate and bidentate coordinated uranium(VI) sulfate in aqueous solution

The coordination of U(VI) sulfate complexes has been investigated by uranium L-III-edge EXAFS and HEXS measurements with the aim to distinguish monodentate and bidentate coordinated sulfate in aqueous solution. UV-vis absorption spectroscopy has been used to differentiate the species and to determine the species distribution as a function of the [SO42-]/[UO22+] ratio. A monodentate coordination prevails in solutions with [SO42-]/[UO22+] ratio of 1, where UO2SO4 is the dominant species. Besides the dominating monodentate sulfate a small amount of bidentate sulfate could be observed, indicating that two isomers may exist for UO2SO4. With increasing [SO42-]/[UO22+] ratio the UP2(SO4)(2)(2-) species becomes the main species. The uranium atom of this species is coordinated by two bidentate Sulfate groups