Characterization of uranyl(VI) nitrate complexes in a room temperature ionic liquid using attenuated total...

Room temperature ionic liquids form potentially important solvents in novel nuclear waste reprocessing methods, and the solvation, speciation, and complexation behaviors of actinides and lanthanides in room temperature ionic liquids is of current interest. In this study, the coordination environment of uranyl(VI) in solutions of the room temperature ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide containing either tetrabutylammonium nitrate or nitric acid was characterized using attenuated total reflection-Fourier transform infrared spectrometry. Both UO(2)(NO(3))(2) and UO(2)(NO(3))(3)(-) species were detected in solutions containing tetrabutylammonium nitrate. ν(as)(UO(2)) for these two species were found to lie at 951 and 944 cm(-1), respectively, while ν(as)(UO(2)) arising from uranyl(VI) coordinated by bis(trifluoromethylsulfonyl)imide anions in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide was found to lie at 968 cm(-1). In solutions containing nitric acid, only UO(2)(NO(3))(2) was detected, due to the high water content. The UO(2)(NO(3))(+) species was not detected under the conditions used in this study. From the results shown here, we conclude that infrared spectroscopy forms a valuable addition to the suite of tools currently used to study the chemical behavior of uranyl(VI) in room temperature ionic liquids.