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A Roadmap to Uranium Ionic Liquids: Anti-Crystal Engineering

TitleA Roadmap to Uranium Ionic Liquids: Anti-Crystal Engineering
Publication TypeJournal Article
Year of Publication2014
AuthorsYaprak, D, Spielberg, ET, Backer, T, Richter, M, Mallick, B, Klein, A, Mudring, AV
JournalChemistry-a European Journal
Date Published05
Type of ArticleArticle
ISBN Number0947-6539
Accession NumberWOS:000335773800036
Keywords1-butyl-3-methylimidazolium, basis-sets, behavior, chloride, Crystal structure, density functional calculations, dithiocarbamate, extraction, Ionic liquids, IR, rn, solubilizing metal-oxides, spectra, Spectroscopy, uranium, uranyl complexes

In the search for uranium-based ionic liquids, tris(N,N-dialkyldithiocarbamato)uranylates have been synthesized as salts of the 1-butyl-3-methylimidazolium (C(4)mim) cation. As dithiocarbamate ligands binding to the UO22+ unit, tetra-, penta-, hexa-, and heptamethylenedithiocarbamates, N,N-diethyldithiocarbamate, N-methyl-N-propyldithiocarbamate, N-ethyl-N-propyldithiocarbamate, and N-methyl-N-butyldithiocarbamate have been explored. X-ray single-crystal diffraction allowed unambiguous structural characterization of all compounds except N-methyl-N-butyldithiocarbamate, which is obtained as a glassy material only. In addition, powder X-ray diffraction as well as vibrational and UV/Vis spectroscopy, supported by computational methods, were used to characterize the products. Differential scanning calorimetry was employed to investigate the phase-transition behavior depending on the N,N-dialkyldithiocarbamato ligand with the aim to establish structure-property relationships regarding the ionic liquid formation capability. Compounds with the least symmetric N,N-dialkyldithiocarbamato ligand and hence the least symmetric anions, tris(N-methyl-N-propyldithiocarbamato)uranylate, tris(N-ethyl-N-propyldithiocarbamato)uranylate, and tris(N-methyl-N-butyldithiocarbamato)uranylate, lead to the formation of (room-temperature) ionic liquids, which confirms that low-symmetry ions are indeed suitable to suppress crystallization. These materials combine low melting points, stable complex formation, and hydrophobicity and are therefore excellent candidates for nuclear fuel purification and recovery.

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