Crystallization in Ionic Liquids: Synthesis, Properties, and Polymorphs of Uranyl Salts

Abstract

Crystallizations in uranyl-containing ionic liquids yielding crystals {X} a {[UO 2 ] b [Y] c } with selected anions and cations (X = [Bmim] + for Y = Cl − , NO 3 − , and SCN − ; Y = Cl − for X = [Emim] + , [Emmim] + , [Bmim] + , and [Bmmim] + ;Emim = l-ethyl-3-methyl-imidazolium, Emmim = l-ethyl-2,3-dimethylimidazolium, Bmim = l-butyl-3-methylimidazolium, and Bmmim = l-butyl-2,3-dimethylimidazolium) were performed herein. Through standard crystallographic analyses, Hirshfeld surface analyses, and multiple characterization techniques, compounds with common cations/anions were investigated. For compounds [Bmim] 2 [(UO 2 ) 2 (μ-OH) 2 (NO 3 ) 4 ] (1), [Bmim] 3 [UO 2 (NCS) 5 ] (2), and [Bmim] 2 [UO 2 Cl 4 ] (3TT and 3TG), common [Bmim] + cations with different conformations were studied with respect to packing and interactions (for 1). The coordinated [(UO 2 ) 2 (μ-OH) 2 (NO 3 ) 4 ] 2− , [UO 2 (NCS) 5 ] 3− , and [UO 2 Cl 4 ] 2− anions that have historically been related to nuclear fuel cycles were demonstrated with respect to geometry and distortion. For compounds with common [UO 2 Cl 4 ] 2− anions [Emim] 2 [UO 2 Cl 4 ] (4), [Emmim] 2 [UO 2 Cl 4 ] (5), [Bmmim] 2 [UO 2 Cl 4 ] (6), 3TT, and 3TG, observed interionic interactions that have been previously impeded by limited structural information were discussed fully in relation to different cations and temperatures. Moreover, multistep phase transformations of 2, which have been undefined in solution studies, have been identified through differential scanning calorimetry analyses and polarizing optical microscopy. The polymorph transformations between 3TT and 3TG in solution, as controlled by uranyl concentration, were studied using optical microscopy and powder X-ray diffraction. The thermal stability, IR/Raman, and UV−vis/luminescence spectra of these compounds were also investigated. ■ INTRODUCTIONIonic liquids (ILs) are attractive to investigators due to their unique physical and chemical properties and have thus been widely examined in many areas. 1,2 Among their usages, crystallization in ILs is a complex and fascinating field of research. 3−5 Both the unique coordination features that cannot generally be observed using molecular solvents and the interaction specifics that are difficult to obtain in the liquid state of ILs can be investigated. 6,7 However, the crystallography data that have immensely promoted our understanding of intermolecular interactions 8 have not been fully explored regarding the crystallographic potential in IL systems.A special interest in f metal-containing ILs has recently arisen in various fields, resulting in many high-quality investigations involving crystallographic studies. 9−12 Specifically, promising applications of ILs in nuclear fuel cycles 13−17 have encouraged extensive studies on uranium-based IL systems, including the relatively common crystallization of uranium salts in ILs and novel explorations of crystallization methods in such complex systems. [3][4][5][6]13,18,19 Using the widely studied uranyl-imidazolium structures as...

Detection and identification of solids, surfaces, and solutions of uranium using vibrational spectroscopy

“…Schnaars and Wilson [125] hypothesized that the 15 cm −1 difference in the symmetric stretching band arose from either 1) additional hydrogen bonding to the uranyl oxo in the monoclinic form or 2) subtle differences in the UACl bond lengths that would lead to an increased electrostatic effect and uranyl bond destabilization. Qu et al demonstrated similar effects by crystallizing the uranyl tetrachloro species with imidazolium cations [126]. An 8 cm −1 difference was observed between [Emim] 2 UO 2 Cl 4 (Emim = 1-ethyl-3-methyl-imidazolium; 827 cm −1 ) and [Emmim] 2 UO 2 Cl 4 (Emmim = 1-ethyl-2,3-dimethylimidazolium; 835 cm −1 ).…”

Uranyl Nitrates: By-Products of the Synthetic Experiments or Key Indicators of the Reaction Progress?

“…There is no information available on the presence of such complexes in the pure inorganic systems. Another distinctive feature of this topology is that the common edge between Ur hexagonal bipyramids is commonly performed by the OH groups (e.g., [32,33]), while lower amount of structures hydroxyl groups are replaced by H 2 O molecules (e.g., [34,35]).…”

Salting‐Out Approach (SOAP) for the Synthesis of Nickel‐Based Coordination Polymer Nanorods from a Dicyanamide Ionic Liquid

“…The constituents of some ILs have ligand binding characteristics. Engineering CPs with ILs expands the range of functional properties that may be readily accessed for emergent applications [8–10] . The negligible volatility of ILs can make it challenging to use solvent evaporation strategies to synthesize IL‐containing CPs.…”

“…Engineering CPs with ILs expands the range of functional properties that may be readily accessed for emergent applications. [8][9][10] The negligible volatility of ILs can make it challenging to use solvent evaporation strategies to synthesize IL-containing CPs. The solvation capacity of certain ILs for metal salts would require the development of strategies to force CP precipitation from the stable metal salt-IL solution.…”