Combined techniques for studying actinide complexes in room temperature ionic liquids

The first coordination sphere of the uranyl cation in room temperature ionic liquids "IL's" results from the competition between its initially bound counterions, the IL anions, and other anions (e.g. present as impurities, or added to the solution). We present a joined spectroscopic (UV-visible and EXAFS) – simulation study of the coordination of uranyl initially introduced either as its UO2X2 salts (X- = nitrate NO3-, triflate Tf-, perchlorate ClO4-) or as UO2(SO4) in a series of imidazolium – based ILs (A- = PF6-, Tf2N-, BF4-), as well as in the Me3NBuTf2N IL. The solubility and dissociation of the uranyl salts are found to depend on the nature of X- and A-. For instance, in the BumimTf2N liquid, UO2(SO4) is insoluble, the UO2(NO3)2 salt dissolves without dissociation, while the UO2(Tf)2 and UO2(ClO4)2 salts are soluble, likely in their complexed and dissociated form, respectively.