[CuCln]2−n Ion-Pair Species in 1-Ethyl-3-methylimidazolium Chloride Ionic Liquid−Water Mixtures: Ultraviolet−Visible, X-ray Absorption Fine Structure, and Density Functional Theory Characterization

Concentrated Ionic Fluids: Is There a Difference Between Chloride-Based Brines and Deep Eutectic Solvents?

Deep Eutectic Solvents (DESs) have been lauded as novel solvents, but is there really a difference between them and concentrated aqueous brines? They provide a method of adjusting the activity of water and chloride ions which can affect mass transport, speciation and reactivity. This study proposes a continuum of properties across concentrated ionic fluids and uses metal processing as an example. Charge transport is shown to be governed by fluidity and there is no discontinuity between molar conductivity and fluidity irrespective of cation, charge density or ionic radius. Diffusion coefficients of iron(III) and copper(II) chloride in numerous concentrated ionic fluids show the same linear correlation between diffusion coefficient and fluidity. These oxidising agents were used to etch copper, silver and nickel and while the etching rate increased with fluidity for copper, etching of silver and nickel only occurred at high chloride and low water activity as passivation occurred when water activity increased. Overall, brines provide a high chloride content at a lower viscosity than DESs, but unlike DESs, brines are unable to prevent passivation due to their high water content. The results show how selective etching of mixed metal waste streams can be achieved by tuning chloride and water activity.

Anion effect on the redox properties of copper ions in ionic liquids and deep eutectic solvents

It has long been claimed that the anion of the DES or IL is critical for controlling the redox properties of metal ions. In this study we investigate the effect of different salt anions on the copper redox properties and speciation, and compare that with the effect of the different solvent anions, when a single copper salt is used in a range of solvents. It is shown that the effect of the solvent anion is much more significant than that of the salt anion on the redox properties. It is also found that copper species remain the same copper tetrachloride species despite the starting salt. An exception is seen for the copper(I) salt, which makes linear dichloride species, as well as the copper(II) acetate system, which displays concentration dependence. When the anion of the ionic liquid is changed, the copper species change correspondingly with the coordinating strength of the solvent anion, leading to a greater difference in redox response, which is due to the different species present. Thus, these speciation differences can be used to modify the redox potentials in the solution.

Evolution of catalytically active species in paired PdCl2-CuCl2/[BMim]Cl for hydrolysis of β-1,4-glycosidic bonds

In this work, we identified the prevailing catalytically active species evolved from paired PdCl2-CuCl2 in 1-butyl-3-methylimidazolium chloride ([BMim]Cl) that displayed dramatic synergism between the two metal chlorides in catalyzing the...

Raman Spectroscopic and Theoretical Study of Scandium Fluoride and Oxyfluoride Anions in Molten FLiNaK

The speciation in the FLiNaK-ScF₃ and FLiNaK-ScF₃-Li₂O melts above 873 K was investigated by Raman spectroscopy and density functional theory (DFT) calculations. Binary scandium fluoride anions in the form of ScF₅^2- and ScF₆^3- were identified in molten FLiNaK containing 20 mol % ScF₃, which were not affected by either temperature or alkali cations in molten fluoride. With the addition of Li₂O into the FLiNaK-ScF₃ (20 mol %) melt, ternary scandium oxyfluoride anion Sc₂OF₆^2- was formed and dominated the spectrum, and it was characterized to possess a linear Sc-O-Sc geometry with two ScF₃ moieties bridged by a single oxygen atom. Further increase in Li₂O content to 40 mol % resulted in the formation of the second oxyfluoride anion Sc₂O₂F₆^4- containing a rhombic Sc₂O₂ ring, while the Raman bands due to Sc₂OF₆^2- disappeared. When the Li₂O concentration went beyond 40 mol %, the sample was no longer homogeneous due to the appearance of insoluble scandium oxide on the surface of the melt, suggesting that scandium oxide is formed via the reactions of ScF₅^2- and ScF₆^3- with O^2- in molten FLiNaK mediated by Sc₂OF₆^2- and Sc₂O₂F₆^4-.

Microwave-assisted ionic liquid-mediated rapid catalytic conversion of non-edible lignocellulosic Sunn hemp fibres to biofuels

Sunn hemp fibre - a cellulose-rich crystalline non-food energy crop, containing 75.6% cellulose, 10.05% hemicellulose, 10.32% lignin, with high crystallinity (80.17%) and degree of polymerization (650) - is identified as a new non-food substrate for lignocellulosic biofuel production. Microwave irradiation is employed to rapidly rupture the cellulose's glycosidic bonds and enhance glucose yield to 78.7% at 160 °C in only 46 min. The reactants - long-chain cellulose, ionic liquid, transition metal catalyst, and water - form a polar supramolecular complex that rotates under the microwave's alternating polarity and rapidly dissipates the electromagnetic energy through molecular collisions, thus accelerating glycosidic bond breakage. In 46 min, 1 kg of Sunn hemp fibres containing 756 g of cellulose produces 595 g of glucose at 160 °C, and 203 g of hydroxymethyl furfural (furanic biofuel precursor) at 180 °C. Yeast mediated glucose fermentation produces 75.6% bioethanol yield at 30 °C, and the ionic liquid is recycled for cost-effectiveness.

Copper(II) Chloro Complex Formation Thermodynamics and Structure in Ionic Liquid, 1-Butyl-3-Methylimidazolium Trifluoromethanesulfonate

Metal ions in ionic liquids are laid under an unprecedented reaction field. In order to assess the reaction thermodynamics of metal ions in such a situation, Cu²⁺-chloro complex formation was examined with spectroscopic and calorimetric titrations in an ionic liquid, 1-buthyl-3-methylimidazolium trifluoromethanesulfonate (C₄mimTfO). In addition, the effect of the structure of the solvated complexes on the complexation mechanism was investigated with the aid of DFT calculations. Chloro complexation successively proceeded and finally provided a [CuCl₄]^2- species, which is also the final product in conventional molecular solvents. Their stability constants were comparable to those in molecular solvents. Interestingly, in spite of the charged solvent in the ionic liquid, the entropy profile of the complexation resembled that in the conventional molecular liquids. This indicates that the entropy gain of the released solvent species from the complexes is the main driving force of the chloro complexation in the ionic liquid. In contrast, unlike the major molecular solvents, the total coordination number of Cu²⁺ is saturated to 4 in the ionic liquid, and the Cl^- complexation tends to be accompanied by a 1:1 exchange of the solvent TfO^- from the complex. In addition, this ligand exchange was almost athermal. This possibly indicates that the coordination number is dominated by the electrostatic hindrance among the ligands including the solvent ions in the primary coordination sphere.

Lewis Acidic Ionic Liquids

Until very recently, the term Lewis acidic ionic liquids (ILs) was nearly synonymous with halometallate ILs, with a strong focus on chloroaluminate(III) systems. The first part of this review covers the historical context in which these were developed, speciation of a range of halometallate ionic liquids, attempts to quantify their Lewis acidity, and selected recent applications: in industrial alkylation processes, in supported systems (SILPs/SCILLs) and in inorganic synthesis. In the last decade, interesting alternatives to halometallate ILs have emerged, which can be divided into two sub-sections: (1) liquid coordination complexes (LCCs), still based on halometallate species, but less expensive and more diverse than halometallate ionic liquids, and (2) ILs with main-group Lewis acidic cations. The two following sections cover these new liquid Lewis acids, also highlighting speciation studies, Lewis acidity measurements, and applications.

An ionic liquid process for mercury removal from natural gas

Efficient ionic liquid based mercury scrubbing technology from gram to ton scale.

Surface state of sacrificial copper electrode by electropolishing in hydrophobic ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

Anodic dissolution of natural surface-oxidized, air-annealed, cathodically reduced, and cathodically deposited copper in hydrophobic ionic liquid 1-buthyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide under galvanostatic conditions by means of gravimetric measurements was studied. The resulting samples were mirror-like oxide-free copper pattern. The mechanism of the electropolishing of oxidized copper surface was considered. The consequent anodic reactions Cu2O - 1e = Cu(+) + CuO, CuO - 2e = Cu(2+) + O, and Cu - 1e = Cu(+) take place. The electropolishing itself occurs over oxygen-free copper surface due to competitive residual water discharge in the pits and copper dissolution on the roughness.