Synthesis of Anhydrous Acetates for the Components of Nuclear Fuel Recycling in Dialkylimidazolium Acetate Ionic Liquids

Formation of Uranyl Peroxide Compounds via Dissolution of Studtite, [(UO2)(O2)(H2O)2](H2O)2, in Ionic Liquids

Four uranyl peroxide compounds with novel structures were formed following the dissolution of studtite, [(UO2)(O2)(H2O)2](H2O)2, in imidazolium-based ionic liquids. The compounds were characterized using single crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD), Raman and infrared (IR) spectroscopy, and scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS). The ionic liquids used in the experiments were 1-ethyl-3-methylimidazolium (EMIm) diethyl phosphate, EMIm ethyl sulfate, and EMIm acetate. Each of the four uranyl peroxide compounds contain components from the ionic liquids as terminal ligands on uranyl peroxide molecular units, bridging ligands in uranyl peroxide sheet structures, or charge balancing cations located in the interstitial space. The studtite dissolved in and reacted with the ionic liquids, producing unique crystal structures depending on the anionic component of the ionic liquid, the temperature at which the synthesis was performed, and the introduction of additional ionic species into the solution. This is the first report of studtite dissolving in and reacting with ionic liquids to form uranyl peroxide compounds, which has the potential to vastly increase the number of synthetic routes for the formation of uranyl peroxide clusters and uranyl peroxide cage clusters.

Fast and non-destructive determination of water content in ionic liquids at varying temperatures by Raman spectroscopy and multivariate regression analysis

Imidazolium acetate ionic liquids (ILs) have been utilized as promising solvents in many applications that involve varying water content and temperature. These experimental variables affect the anion-cation intermolecular interactions, which in turn influence the performance of the ILs in these applications. This paper shows Raman spectroscopy can be used as an operando method to measure water content in IL solvents when simultaneous temperature changes may occur. The Raman spectra of 1-alkyl-3-methylimidazolium acetate ILs (alkyl chain length n = 2, 4, 6, 8) with varying water content (from 0.028 to 0.899 water mole fraction) and temperature (from 78.1 K to 423.1 K) were measured. Increasing the water content or decreasing the temperature of the tested ILs weakens the anion-cation intermolecular interactions. The water content of these ILs can be quantified even in conditions when the temperature is changing using Raman spectroscopy combined with multivariate regression analysis, including principal component regression (PCR), partial-least-squares regression (PLSR), and artificial neural networks (ANNs). The ANN model combined with partial-least-squares (PLS) achieved the highest prediction accuracy of water content in ILs at varying temperatures (RMSECV = 0.017, R²_CV = 99.1%, RMSEP = 0.019, R²_P = 98.8%, RPD = 8.93). Raman spectroscopy provides a potential fast non-destructive operando method to monitor the water content of ILs even in applications when the temperature may be simultaneously altered; this information can lead to the optimized use of these ILs in many applications.

Ready Access to Anhydrous Anionic Lanthanide Acetates by Using Imidazolium Acetate Ionic Liquids as the Reaction Medium

Access to lanthanide acetate coordination compounds is challenged by the tendency of lanthanides to coordinate water and the plethora of acetate coordination modes. A straightforward, reproducible synthetic procedure by treating lanthanide chloride hydrates with defined ratios of the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([C2 mim][OAc]) has been developed. This reaction pathway leads to two isostructural crystalline anhydrous coordination complexes, the polymeric [C2 mim]n [{Ln2 (OAc)7 }n ] and the dimeric [C2 mim]2 [Ln2 (OAc)8 ], based on the ion size and the ratio of IL used. A reaction with an IL : Ln-salt ratio of 5 : 1, where Ln=Nd, Sm, and Gd, led exclusively to the polymer, whilst for the heaviest lanthanides (Dy-Lu) the dimer was observed. Reaction with Eu and Tb resulted in a mixture of both polymeric and dimeric forms. When the amount of IL and/or the size of the cation was increased, the reaction led to only the dimeric compound for all the lanthanide series. Crystallographic analyses of the resulting salts revealed three different types of metal-acetate coordination modes where η2 μκ2 is the most represented in both structure types.

Speciation of Ionic Uranyl-Containing Complexes in in Situ Formed Dicyanonitrosomethanide-Based Ionic Liquids

A series of ionic uranyl-containing complexes, namely [C₂mim]₂[UO₂(ccnm)₄] (1), [C₄mim]₂[UO₂(ccnm)₄] (2), [N₁₁₁₁]₂[UO₂(ccnm)₄][H₂O]₂ (3), and [P₂₄₄₄]₂[UO₂(dcnm)₂(ccnm)₂] (4) [(ccnm)^- = carbamoylcyanonitrosomethanide; dcnm = dicyanonitrosomethanide; (C₂mim)⁺ = 1-ethyl-3-methylimidazolium; (C₄mim)⁺ = 1-butyl-3-methylimidazolium; (N₁₁₁₁)⁺ = tetramethylammonium; (P₂₄₄₄)⁺ = tributyl(ethyl)phosphonium)], were isolated from in situ formed dcnm-based ionic liquids and characterized systematically. It was found that the dcnm anions transformed into ccnm anions during the reactions. These anions coordinate with the uranyl cations in chelate or terminal monodentate coordination mode, affording negative divalent complex anions which can combine with different organic cations and form ionic uranyl-containing complexes. Plenty of C-H···O, N-H···O, C-H···N, N-H···N, and H···H weak interactions are formed in the crystal structures. The transformation of cyano to amide groups contributes to the crystallinity and leads to higher melting points as well as the luminescence quenching of these compounds.

Reaction of Cu(II) Chelates with Uranyl Nitrate to Form a Coordination Complex or H-Bonded Adduct: Experimental Observations and Rationalization by Theoretical Calculations

Four new heterometallic Cu(II)-U(VI) species, [{(CuL¹)(CH₃CN)}UO₂(NO₃)₂] (1), [{(CuL²)(CH₃CN)}UO₂(NO₃)₂] (2), [{(CuL³)(H₂O)}UO₂(NO₃)₂] (3), and [UO₂(NO₃)₂(H₂O)₂]·2[CuL⁴]·H₂O (4), were synthesized using four different metalloligands ([CuL¹], [CuL²], [CuL³], and [CuL⁴], respectively) derived from four unsymmetrically dicondensed N,O-donor Schiff bases. Single-crystal structural analyses revealed that complexes 1, 2, and 3 have a discrete dinuclear [Cu-UO₂] core in which one metalloligand, [CuL], is connected to the uranyl moiety via a double phenoxido bridge. Two chelating nitrate ions complete the octa-coordination around uranium. Species 4 is a cocrystal, where a uranyl nitrate dihydrate is sandwiched between two metalloligands [CuL⁴] by the formation of strong hydrogen bonds between the H atoms of the coordinated water molecules to U(VI) and the O atoms of [CuL⁴]. Spectrophotometric titrations of these four metalloligands with uranyl nitrate dihydrate in acetonitrile showed a well-anchored isosbestic point between 300 and 500 nm in all cases, conforming with the coordination of [CuL¹], [CuL²], [CuL³], and the H-bonding interaction of [CuL⁴] with UO₂(NO₃)₂. This behavior of [CuL⁴] was utilized to selectively bind metal ions (e.g., Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, and La³⁺) in the presence of UO₂(NO₃)₂·2H₂O in acetonitrile. The formation of these Cu(II)-U(VI) species in solution was also evaluated by steady-state fluorescence quenching experiments. The difference in the coordination behavior of these metalloligands toward [UO₂(NO₃)₂(H₂O)₂] was studied by density functional theory calculations. The lower flexibility of the ethylenediamine ring and a large negative binding energy obtained from the evaluation of H bonds and supramolecular interactions between [CuL⁴] and [UO₂(NO₃)₂(H₂O)₂] corroborate the formation of cocrystal 4. A very good linear correlation (r² = 0.9949) was observed between the experimental U═O stretching frequencies and the strength of the equatorial bonds that connect the U atom to the metalloligand.

The presence of mixed-valent silver in the uranyl phenylenediphosphonate framework

A 2-D silver uranyl phosphonate presents both Ag⁺ and Ag⁰ atoms in the free space between the adjacent layers and the incorporation of the mixed-valent silver sites results in the quenching of the fluorescent emission.