Nonstoichiometric, Protic Azolium Azolate Ionic Liquids Provide Unique Environments for N-Donor Coordination Chemistry

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

A series of anhydrous acetate salts with uranium {[C₂C₁im][UO₂(OAc)₃] (1), [C₂C₂im][UO₂(OAc)₃] (2), and [C₄C₁im][UO₂(OAc)₃] (3)}, lanthanides {[C₂C₂im]₂[La(OAc)₅] (4) and [C₂C₁im]₂[Nd(OAc)₅] (5)}, and strontium {[C₂C₁im]_n[Sr(OAc)₃]_n (6)} (where C₂C₁im = 1-ethyl-3-methylimidazolium, C₂C₂im = 1,3-diethylimidazolium, C₄C₁im = 1-butyl-3-methylimidazolium, and OAc = acetate) have been prepared and structurally characterized. Both lanthanides and strontium are common components of the nuclear fuel waste, and their separation from uranium is an important but still challenging task. A new synthetic approach with dialkylimidazolium acetate ionic liquids (ILs) as the solvent has been developed for the direct synthesis of homoleptic acetates from the corresponding hydrates and, unexpectedly, hardly soluble f-element oxides. Although the group of characterized compounds shows perfect structural variability, all actinide and lanthanide metal ions form monomeric complex anions where the metal cation coordinates to five ligands including two oxygen atoms in the case of uranium, as is commonly observed for uranyl compounds. Crystallographic analyses revealed that the complex [UO₂(OAc)₃]^- anions possess rather standard D_3h symmetry featuring a hexagonal-bipyramidal coordination environment, while the lanthanide anions [Ln(OAc)₅]^2- are fully asymmetric and the Ln³⁺ cations are 10-coordinated in the form of a distorted bicapped tetragonal antiprism. This is the first report of lanthanide ions coordinated in this fashion. For Sr²⁺, 9-fold coordination through oxygen atoms in the form of a strongly distorted tricapped trigonal prism is observed. The crystallization of anhydrous, homoleptic, anionic acetate complexes from such a large variety of different metal salts appears to be due to the properties of dialkylimidazolium acetate ILs themselves, including enhanced basicity from the high concentration of free anions and their greater affinity for hydrogen-bonding solutes relative to metal cations.

The crystal structure of hexakis(1-isopropyl-1H-imidazole-κ1N)copper(II) dichloride, C36H58Cl2CuN12

C36H58Cl2CuN12, monoclinic, P21/c (no. 14), a = 8.1490(8) Å, b = 17.0301(15) Å, c = 16.8649(14) Å, β = 101.629(3)°, Z = 2, V = 2292.4(4) Å3, Rgt(F) = 0.0419, wRref(F2) = 0.1121, T = 298(2) K.

Activation of the Cyano Group at Imidazole via Copper Stimulated Alcoholysis

Reactions of 4,5-dicyano-1-methylimidazole with CuX2 (X = Cl, Br) in alcohol solvents (ethanol and methanol) resulted in the formation of Cu(II) carboximidate complexes [CuCl2(5- cyano-4-C(OEt)N-1-methylimidazole)(EtOH)] (1), [Cu2(µ-Cl)2Cl2(5-cyano-4-C(OMe)N-1-methylimidazole)2] (2), [Cu2(µ-Br)2Br2(5-cyano-4-C(OMe)N-1-methylimidazole)2] (3), and [Cu2(µ-Br)2Br2(5-cyano-4-C(OEt)N-1-methylimidazole)2] (4). The structures were determined by the X-ray crystallographic method, and further spectroscopic and computational methods were employed to explain the structural features. The solvent contributed to the alcoholysis reaction of the cyano group, as the result of which the ligand coordinated to the metal center in bidentate mode forming a five-membered chelating ring. In 1, the solvent also acts as an additional ligand, which coordinates to the metal center of a monomeric complex. In compounds 2–4, two halogen ligands link the metal atoms forming dihalo-bridged copper dimers. The infrared absorption characteristics were verified by simulation of the infrared spectra at the density functional theory level. In addition, the electronic absorption characteristics were explained by simulation of the UV–Vis spectra using the TD-DFT method. Molecular modelling at the DFT level was performed to study the effects of halogen type and steric hindrance of the alkoxy groups in forming the copper(II) complexes.

Azolate Anions in Ionic Liquids: Promising and Under-Utilized Components of the Ionic Liquid Toolbox

Owing to their ease of synthesis, diffuse positive charge, and chemical stability, 1-alkyl-3-methylimidazolium cations (i.e., [C_n mim]⁺ ) are one of the most routinely utilized and historically important components in ionic liquid (IL) chemistry. However, while this is a routinely encountered member of the IL family as cations, relatively few workers have explored the versatile chemistry of azoles to allow their use as an anionic component in ILs, as azolates. Azolate anions possess many of the desired properties for IL formation, including a diffuse ionic charge, tailorable asymmetry, and synthetic flexibility, with the added advantages of not relying on halogen atoms for electron-withdrawing effects, as is commonly encountered with IL anions such as hexafluorophosphate. This review explores the 122 azolate-containing ILs known in the literature (prepared from only 39 disparate azolate anions), with a view to highlighting not only their demonstrated utility as an IL component, but the ways in which the larger scientific community may utilize their advantageous properties for new tailored materials.

Structure-property relationships in protic ionic liquids: a study of solvent-solvent and solvent-solute interactions

The ionic nature of a functionalized protic ionic liquid cannot be rationalized simply through the differences in aqueous proton dissociation constants between the acid precursor and the conjugate acid of the base precursor. The extent of proton transfer, i.e. the equilibrium ionicity, of a tertiary ammonium acetate protic ionic liquid can be significantly increased by introducing an hydroxyl functional group on the cation, compared to the alkyl or amino-functionalized analogues. This increase in apparent ionic nature correlates well with variations in solvent-solute and solvent-solvent interaction parameters, as well as with physicochemical properties such as viscosity.

Formation of ionic co-crystals of amphoteric azoles directed by the ionic liquid co-former 1-ethyl-3-methylimidazolium acetate

The ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate was utilized as a liquid-state crystallization agent to form ionic co-crystals using amphoteric azoles selected as model compounds for active pharmaceutical ingredients. Weakly acidic azoles crystallize the IL relatively quickly, while stronger acidic azoles undergo slower ion exchange with the IL to form salts.