Structural study on uranyl ion in 1-butyl-3-methylimidazolium nonafluorobutanesulfonate ionic liquid |
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Authors: | Koichiro Mizuoka Yasuhisa Ikeda |
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Affiliation: | Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, 2-12-1-N1-34, O-okayama, Meguro-ku, Tokyo 152-8550, Japan |
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Abstract: | The structure of uranyl ion in 1-butyl-3-methylimidazolium nonafluorobutanesulfonate ionic liquid (BMINfO) has been studied with 1H- and 35Cl-NMR, Raman, and UV-visible spectroscopy. In the 1H-NMR spectrum of the BMINfO solution prepared by dissolving UO2(ClO4)2·5 6H2O, the signal of H2O coordinated to UO22+ was observed at 6.64 ppm at 50°C (free H2O in BMINfO: 3.1 ppm at 50°C), suggesting that the uranyl species exists as the aquo complex, UO2(H2O)n]2+. The signal of the coordinated H2O disappears with heating at 120°C for 3 h under vacuum. This indicates the dehydration from UO2(H2O)n]2+. On the other hand, the 35Cl-NMR signal of ClO4− as the counter anion of UO22+ was observed at 1011 ppm (vs. Cl− in D2O) regardless of heating. This indicates that no ClO4− ion is in the first coordination sphere of UO22+. Furthermore, the UV-visible absorption spectra showed that the characteristic absorption bands due to UO22+ were sharpened with the dehydration. This means the simplification of the structure around UO22+. These results described above suggest that UO22+ in BMINfO has no ligand in its equatorial plane after the dehydration, i.e. UO22+ exists as a bare cation in this system. |
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Keywords: | Uranyl ion Ionic liquid Chemical structure BMINfO |
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