title: A roadmap to uranium ionic liquids: anti-crystal engineering.
abstract: In the search for uranium-based ionic liquids, tris(N,N-dialkyldithiocarbamato)uranylates have been synthesized as salts of the 1-butyl-3-methylimidazolium (C4mim) cation. As dithiocarbamate ligands binding to the UO2(2+) 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.
authors.affiliation: Inorganic Chemistry III, Ruhr-University Bochum, Universitätsstrasse 150, 44801 Bochum (Germany), Fax: (+49) 234-32-14951.
authors.forename: Damla
authors.initials: D
authors.lastname: Yaprak
authors.forename: Eike T
authors.initials: ET
authors.lastname: Spielberg
authors.forename: Tobias
authors.initials: T
authors.lastname: Bäcker
authors.forename: Mark
authors.initials: M
authors.lastname: Richter
authors.forename: Bert
authors.initials: B
authors.lastname: Mallick
authors.forename: Axel
authors.initials: A
authors.lastname: Klein
authors.forename: Anja-Verena
authors.initials: AV
authors.lastname: Mudring
keywords: IR spectroscopy; crystal structure; density functional calculations; ionic liquids; uranium