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Ionic liquids (ILs) are a unique class of solvents with potential applications in advanced separation technologies relevant to the nuclear industry. ILs are salts with low melting points and a wide range of tunable physical properties, such as viscosity, hydrophobiciy, conductivity, and liquidus range. ILs have negligible vapor pressure, are often non-flammable, and can have high thermal stability and a wide electrochemical window, making them attractive for use in separations processes relevant to the nuclear industry. Metal salts generally have a low solubility in ILs; however, by incorporating new functional groups into the IL cation or anion that promote complexation with the metal, the solubility can be greatly increased. One such task-specific ionic liquid (TSIL) is 1-carboxy-N, N, N-trimethylglycine bis(trifluoromethylsulfonyl)imide ([Hbet][Tf2N]) [Nockemann et al., J. Phys. Chem. B 110, 20978–20992 (2006)]. Water, which is detrimental for electrochemical separations, is a common impurity in ILs and can coordinate with actinyl cations, particularly in ILs containing only weakly coordinating components. Understanding the behavior of actinides in TSIL/water mixtures on a molecular level is vital for designing improved separations processes. Classical molecular dynamics simulations of uranyl(VI) and plutonyl(VI) in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][Tf2N]) with deprotonated Hbet (betaine) and water have been performed to understand the coordination and dynamics of the actinyl cations. We find that betaine is a much stronger ligand than water and prefers to coordinate the metal in a bidentate manner. Potential of mean force simulations yield a relative free energy for betaine coordination of approximately −120 to −90 kJ/mol in mixtures with water. As the amount of betaine coordinated to the actinide increases, the diffusion coefficient of the actinyl cation decreases. Moreover, the betaine ligand is able to bridge between two metal centers, resulting in dimeric complexes with actinide–actinide distances of ∼5 Å. Potential of mean force simulations show that these structures are stable, with relative free energies of up to −40 kJ/mol. The crystal structure for [(UO2)2(bet)6(H2O)2][Tf2N]4 shows that the betaine bridges between two uranium atoms to form dimeric complexes similar to those found in our simulations [Nockemann et al. Inorg. Chem. 49, 3351–33601 (2010)]. [ABSTRACT FROM AUTHOR]

The spectroscopic characterization and thermodynamic stability of the mixed-ligand complex, U[O.sub.2]([O.sub.2])[(C[O.sub.3]).sub.2.sup.4-], is described in both solution and solid state. The studies have shown that the stable solution species is U[O.sub.2]([O.sub.2])[(C[O.sub.3]).sub.2.sup.4-], which has a formation constant that is relative to the tris-carbonato complex.

The structural determination of the ionic liquid, caesium bis­[(tri­fluoro­meth­yl)sulfon­yl]imide or poly[[μ4-bis­[(tri­fluoro­meth­yl)sulfon­yl]imido]caesium(I)], Cs[N(SO2CF3)2] or Cs[Tf2N], reveals a second polymorph that also crystallizes in a layer structure possessing monoclinic P21/c symmetry at 120 K instead of C2/c for the known polymorph [Xue et al. (2002). Solid State Sci. 4, 1535–1545]. The caesium ions in the cationic layers are coordinated by the sulfonyl groups of the bis­triflimide mol­ecules from anion layers while the tri­fluoro­methyl groups are oriented in the opposite direction, forming a non-polar surface separating the layers. The layer direction is (100). [ABSTRACT FROM AUTHOR]

Intra- and intermolecular force field parameters for the interaction of actinyl ions (AnO2n+, where, An = U, Np, Pu, Am and n = 1, 2) with water have been developed using quantum mechanical calculations. Water was modeled with the extended simple point charge potential (SPC/E). The resulting force field consists of a simple form in which intermolecular interactions are modeled with pairwise Lennard-Jones functions plus partial charge terms. Intramolecular bond stretching and angle bending are treated with harmonic functions. The new potentials were used to carry out extensive molecular dynamics simulations for each hydrated ion. Computed bond lengths, bond angles and coordination numbers agree well with known values and previous simulations. Hydration free energies, computed from molecular dynamics simulations as well as from quantum simulations with a solvation model, were in reasonable agreement with estimated experimental values. [ABSTRACT FROM AUTHOR]

A fundamental understanding of thebehavior of actinides in ionicliquids is required to develop advanced separation technologies. Spectroscopicmeasurements indicate a change in the coordination of uranyl in thehydrophobic ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide([EMIM][Tf2N]) as water is added to the system. Moleculardynamics simulations of dilute uranyl (UO22+) and plutonyl (PuO22+) solutionsin [EMIM][Tf2N]/water mixtures have been performed in orderto examine the molecular-level coordination and dynamics of the actinylcation (AnO22+); An = U, Pu) as the amount of water in the system changes. Thesimulations show that the actinyl cation has a strong preference fora first solvation shell with five oxygen atoms, although a highercoordination number is possible in mixtures with little or no water.Water is a much stronger ligand for the actinyl cation than Tf2N, with even very small amounts of water displacing Tf2N from the first solvation shell. When enough water is present,the inner coordination sphere of each actinyl cation contains fivewater molecules without any Tf2N. Water also populatesthe second solvation shell, although it does not completely displacethe Tf2N. At high water concentrations, a significant fractionof the water is found in the bulk ionic liquid, where it primarilycoordinates with the Tf2N anion. Potential of mean forcesimulations show that the progressive addition of up to five watermolecules to uranyl is very favorable, with ΔGranging from −52.3 kJ/mol for the addition of the first watermolecule to −37.6 kJ/mol for the addition of the fifth. Uranyland plutonyl dimers formed via bridging Tf2N ligands arefound in [EMIM][Tf2N] and in mixtures with very small amountsof water. Potential of mean force calculations confirm that the dimericcomplexes are stable, with relative free energies of up to −9kJ/mol in pure [EMIM][Tf2N]. We find that the self-diffusioncoefficients for all the components in the mixture increase as thewater content increases, with the largest increase for water and thesmallest increase for the ionic liquid cation and anion. The velocityautocorrelation functions also indicate changes in structure and dynamicsas the water content changes. [ABSTRACT FROM AUTHOR]

As a precursor of carboxyl-functionalized task-specific ionic liquids (TSILs) for f-element separations, (pyrazol-l-yl)acetic add (L) can be deprotonated as a functionalized pyrazolate anion to coordinate with hard metal cations. However, the coordination chemistry of L with f-dements remains unexplored. We reacted L with lanthanides in aqueous solution at pH = S and synthesized four lanthanide complexes of general formula [Ln(L)3(H20)2]-nHi0 (l, Ln = La, n = 2; 2, Ln = Ce, n = 2; 3, Ln = Pr, n = 2; 4, Ln = Nd, n = l). All complexes were characterized by single crystal X-ray diffraction analysis revealing one-dimensional chain formations. Two distinct crystallographic structures are governed by the different coordination modes of carboxylate groups in L: terminal bidentate and bridging tridentate (l-- 3); terminal bidentate, bridging bidentate, and tridentate coordination in 4. Comparison of the solid state UV--vis--NIR diffuse reflectance spectra with solution state UV--vis--NIR spectra suggests a different spedes in solution and solid state. The different coordination in solid state and solution was verified by distinctive, 3C NMR signals of the carboxylate groups in the solid state NMR. [ABSTRACT FROM AUTHOR]

Despite the wide range of applications of ɑ-hydroxyisobutyric acid (HIBA) in biochemical processes, pharmaceutical formulations, and group and elemental separations of lanthanides and actinides, the structures and geometries of lanthanide--HIBA complexes are still not well understood. We reacted HIBA with lanthanides in aqueous solution at pH = 5 and synthesized 14 lanthanide--HIBA complexes of the formula [Ln(HIBA)2(H2O)2](NO3)⋅H2O (Ln = La (1), Ce (2), Pr (3), Nd (4), Sm (5), Eu (6), Gd (7), Tb (8), Dy (9), Ho (10), Er (11), Tm (12), Yb (13), Lu (14)), isolating single crystals (1-7, 10, and 11) and powders (8, 9, and 12-14). Both single-crystal and powder X-ray diffraction studies reveal a two-dimensional extended structure across the entire lanthanide series. The environment around the eight-coordinated Ln(III) atom is best described as a distorted dodecahedron, where HIBA acts as a monoanionic tridentate ligand with one carboxylato oxygen atom and one hydroxyl oxygen atom chelating to one Ln(III) center. The carboxylato oxygen atom from a second HIBA ligand bridges to a neighboring Ln(III) atom to form a two-dimensional extended structure. While the coordination mode for HIBA is identical across the lanthanide series, three different structure types are found for La, Ce--Ho, and Er--Lu. Solution characterization using 13C NMR further confirmed a single solution complex under the crystallization conditions. Raman and UV--vis--NIR absorbance and diffuse reflectance spectra of HIBA--Ln (III) complexes were also measured. [ABSTRACT FROM AUTHOR]