Ionic Liquids Based on the Concept of Melting Point Lowering Due to Ethoxylation

Most of the commonly used Ionic Liquids (ILs) contain bulky organic cations with suitable anions. With our COMPLET (Concept of Melting Point Lowering due to Ethoxylation), we follow a different approach. We use simple, low-toxic, cheap, and commercially available anions of the type C_x(EO)_yCH₂COO^– to liquefy presumably any simple metal ion, independently of its charge. In the simplest case, the cation can be sodium or lithium, but synthesis of Ionic Liquids is also possible with cations of higher valences such as transition or rare earth metals. Anions with longer alkyl chains are surface active and form surface active ionic liquids (SAILs), which combine properties of ionic and nonionic surfactants at room temperature. They show significant structuring even in their pure state, i.e., in the absence of water or any other added solvent. This approach offers new application domains that go far beyond the common real or hypothetical use of classical Ionic Liquids. Possible applications include the separation of rare earth metals, the use as interesting media for metal catalysis, or the synthesis of completely new materials (for example, in analogy to metal organic frameworks).     

Synthesis of New Lipid‐Inspired Ionic Liquids by Thiol‐ene Chemistry: Profound Solvent Effect on Reaction Pathway

The synthesis of a series of new lipid‐inspired ionic liquids through thiol‐ene “click” reaction with a single‐step process. This synthesis offers considerable promise as an efficient and orthogonal method to construct structurally diverse imidazolium‐type ionic liquids with linear and branched cationic tails, as well as versatility in the placement of the sulfur heteroatom. Profound solvent effect in this ene reaction regioselectivity has been observed.     

Understanding the Effect Models of Ionic Liquids in the Synthesis of NH4‐Dw and γ‐AlOOH Nanostructures and Their Conversion into Porous γ‐Al2O3

Well‐dispersed ammonium aluminum carbonate hydroxide (NH₄‐Dw) and γ‐AlOOH nanostructures with controlled morphologies have been synthesized by employing an ionic‐liquid‐assisted hydrothermal process. The basic strategies that were used in this work were: 1) A controllable phase transition from NH₄‐Dw to γ‐AlOOH could be realized by increasing the reaction temperature and 2) the morphological evolution of NH₄‐Dw and γ‐AlOOH nanostructures could be influenced by the concentration of the ionic liquid. Based on these experimental results, the main objective of this work was to clarify the effect models of the ionic liquids on the synthesis of NH₄‐Dw and γ‐AlOOH nanostructures, which could be divided into cationic‐ or anionic‐dominant effect models, as determined by the different surface structures of the targets. Specifically, under the cationic‐dominant regime, the ionic liquids mainly showed dispersion effects for the NH₄‐Dw nanostructures, whereas the anionic‐dominant model could induce the self‐assembly of the γ‐AlOOH particles to form hierarchical structures. Under the guidance of the proposed models, the effect of the ionic liquids would be optimized by an appropriate choice of cations or anions, as well as by considering the different effect models with the substrate surface. We expect that such effect models between ionic liquids and the target products will be helpful for understanding and designing rational ionic liquids that contain specific functional groups, thus open up new opportunities for the synthesis of inorganic nanomaterials with new morphologies and improved properties. In addition, these as‐prepared NH₄‐Dw and γ‐AlOOH nanostructures were converted into porous γ‐Al₂O₃ nanostructures by thermal decomposition, whilst preserving the same morphology. By using HRTEM and nitrogen‐adsorption analysis, the obtained γ‐Al₂O₃ samples were found to have excellent porous properties and, hence, may have applications in catalysis and adsorption.     

Applying the Inductive Effect for Synthesizing Low‐Melting and Low‐Viscosity Imidazolium‐Based Ionic Liquids

Fluidizing ionic liquids: By applying the inductive effect, a synthesis strategy to introduce strong, directional and localized H‐bonds into imidazolium‐based ionic liquids is proposed. In opposite to H‐bonded molecular liquids these strong H‐bonds could reduce the melting points and decrease the viscosities of the ILs (see figure).

     

X‐ray Photoelectron Spectroscopy of Pyridinium‐Based Ionic Liquids: Comparison to Imidazolium‐ and Pyrrolidinium‐Based Analogues

We investigate eight 1‐alkylpyridinium‐based ionic liquids of the form [C_nPy][A] by using X‐ray photoelectron spectroscopy (XPS). The electronic environment of each element of the ionic liquids is analyzed. In particular, a reliable fitting model is developed for the C 1s region that applies to each of the ionic liquids. This model allows the accurate charge correction of binding energies and the determination of reliable and reproducible binding energies for each ionic liquid. Shake‐up/off phenomena are determinedfor both C 1s and N 1s spectra. The electronic interaction between cations and anions is investigated for both simple ionic liquids and an example of an ionic‐liquid mixture; the effect of the anion on the electronic environment of the cation is also explored. Throughout the study, a detailed comparison is made between [C₈Py][A] and analogues including 1‐octyl‐1‐methylpyrrolidinium‐ ([C₈C₁Pyrr][A]), and 1‐octyl‐3‐methylimidazolium‐ ([C₈C₁Im][A]) based samples, where X is common to all ionic liquids.     

Self‐Assembly of Imidazolium‐Based Surfactants in Magnetic Room‐Temperature Ionic Liquids: Binary Mixtures

The phase behaviour of binary mixtures of ionic surfactants (1‐alkyl‐3‐imidazolium chloride, C_nmimCl with n=14, 16 and 18) and imidazolium‐based ionic liquids (1‐alkyl‐3‐methylimidazolium tetrachloroferrate, C_nmimFeCl₄, with n=2 and 4) over a broad temperature range and the complete range of compositions is described. By using many complementary methods including differential scanning calorimetry (DSC), polarised microscopy, small‐angle neutron and X‐ray scattering (SANS/SAXS), and surface tension, the ability of this model system to support self‐assembly is described quantitatively and this behaviour is compared with common water systems. The existence of micelles swollen by the solvent can be deduced from SANS experiments and represent a possible model for aggregates, which has barely been considered for ionic‐liquid systems until now, and can be ascribed to the rather low solvophobicity of the surfactants. Our investigation shows that, in general, C_nmimCl is a rather weak amphiphile in these ionic liquids. The amphiphilic strength increases systematically with the length of the alkyl chain, as seen from the phase behaviour, the critical micelle concentration, and also the level of definition of the aggregates formed.     

Coupling‐Reagent‐Free Synthesis of Dipeptides and Tripeptides Using Amino Acid Ionic Liquids

A general method for the synthesis of dipeptides has been developed, which does not require any coupling reagents. This method is based on the reaction of readily available HCl salts of amino acid methyl esters with tetrabutylphosphonium amino acid ionic liquids. The isolation procedure of stepwise treatment with AcOH is easy to carry out. The method was extended to the synthesis of tripeptide, tyrosyl‐glycyl‐glycine, present in IMREG‐1, also.     

Synthesizing 2D and 3D Selenidostannates in Ionic Liquids: The Synergistic Structure‐Directing Effects of Ionic Liquids and Metal–Amine Complexes

Presented are the ionothermal syntheses, characterizations, and properties of a series of two‐ and three‐dimensional selenidostannate compounds synergistically directed by metal–amine complex (MAC) cations and ionic liquids (ILs) of [Bmmim]Cl (Bmmim=1‐butyl‐2,3‐dimethylimidazolium). Four selenidostannates, namely, 2D‐(Bmmim)₃[Ni(en)₃]₂[Sn₉Se₂₁]Cl ( 1 , en=ethylenediamine), 2D‐(Bmmim)₈[Ni₂(teta)₂(μ‐teta)]Sn₁₈Se₄₂ ( 2 , teta=triethylenetetramine), 2D‐(Bmmim)₄[Ni(tepa)Cl]₂[Ni(tepa)Sn₁₂Se₂₈] ( 3 , tepa=tetraethylenepentamine), and 3D‐(Bmmim)₂[Ni(1,2‐pda)₃]Sn₈Se₁₈ ( 4 , 1,2‐pda=1,2‐diaminopropane), were obtained. Single‐crystal X‐ray diffraction analyses revealed that compounds 1 and 2 possess a lamellar anionic [Sn₃Se₇]_n^2n? structure comprising distinct eight‐membered ring units, whereas 3 features a MAC‐decorated anionic [Ni(tepa)Sn₁₂Se₂₈]_n^6n? layered structure. In contrast to 1 – 3 , compound 4 exhibits a 3D open framework of anionic [Sn₄Se₉]_n^2n?. The structural variation from 1 to 4 clearly indicates that on the basis of the synergistic structure‐directing ability of the MACs and ILs, variation of the organic polyamine ligand has a significant impact on the formation of selenidostannates.     

Synthesis and Properties of Alkoxy‐ and Alkenyl‐Substituted Peralkylated Imidazolium Ionic Liquids

Novel peralkylated imidazolium ionic liquids bearing alkoxy and/or alkenyl side chains have been synthesized and studied. Different synthetic routes towards the imidazoles and the ionic liquids comprising bromide, iodide, methanesulfonate, bis(trifluoromethylsulfonyl)imide ([NTf₂]^?), and dicyanamide {[N(CN)₂]^?} as the anion were evaluated, and this led to a library of analogues, for which the melting points, viscosities, and electrochemical windows were determined. Incorporation of alkenyl moieties hindered solidification, except for cations with high symmetry. The alkoxy‐derivatized ionic liquids are often crystalline; however, room‐temperature ionic liquids (RTILs) were obtained with the weakly coordinating anions [NTf₂]^? and [N(CN)₂]^?. For the viscosities of the peralkylated RTILs, an opposite trend was found, that is, the alkoxy derivatives are less viscous than their alkenyl‐substituted analogues. Of the crystalline compounds, X‐ray diffraction data were recorded and related to their molecular properties. Upon alkoxy substitution, the electrochemical cathodic limit potential was found to be more positive, whereas the complete electrochemical window of the alkenyl‐substituted imidazolium salts was shifted to somewhat more positive potentials.     

Thermomorphic Behavior of the Ionic Liquids [C4mim][FeCl4] and [C12mim][FeCl4]

The iron‐containing ionic liquids 1‐butyl‐3‐methylimidazolium tetrachloroferrate(III) [C₄mim][FeCl₄] and 1‐dodecyl‐3‐methylimidazolium tetrachloroferrate(III) [C₁₂mim][FeCl₄] exhibit a thermally induced demixing with water (thermomorphism). The phase separation temperature varies with IL weight fraction in water and can be tuned between 100 °C and room temperature. The reversible lower critical solution temperature (LCST) is only observed at IL weight fractions below ca. 35 % in water. UV/Vis, IR, and Raman spectroscopy along with elemental analysis prove that the yellow‐brown liquid phase recovered after phase separation is the starting IL [C₄mim][FeCl₄] and [C₁₂mim][FeCl₄], respectively. Photometry and ICP‐OES show that about 40 % of iron remains in the water phase upon phase separation. Although the process is thus not very efficient at the moment, the current approach is the first example of an LCST behavior of a metal‐containing IL and therefore, although still inefficient, a prototype for catalyst removal or metal extraction.     

Novel Biocompatible and Self‐buffering Ionic Liquids for Biopharmaceutical Applications

Antibodies obtained from egg yolk of immunized hens, immunoglobulin Y (IgY), are an alternative to the most focused mammal antibodies, because they can be obtained in higher titers by less invasive approaches. However, the production cost of high‐quality IgY for large‐scale applications remains higher than that of other drug therapies due to the lack of efficient purification methods. The search for new purification platforms is thus vital. The solution could be liquid–liquid extraction by using aqueous biphasic systems (ABS). Herein, we report the extraction and attempted purification of IgY from chicken egg yolk by using a new ABS composed of polymers and Good’s buffer ionic liquids (GB‐ILs). New self‐buffering and biocompatible ILs based on the cholinium cation and anions derived from Good’s buffers were synthesized and the self‐buffering characteristics and toxicity were characterized. Moreover, when these GB‐ILs are combined with PPG 400 (poly(propylene) glycol with a molecular weight of 400 g mol^‐1) to form ABS, extraction efficiencies, of the water‐soluble fraction of proteins, ranging between 79 and 94 % were achieved in a single step. Based on computational investigations, we also demonstrate that the preferential partitioning of IgY for the GB‐IL‐rich phase is dominated by hydrogen‐bonding and van der Waals interactions.     

Studies on the Solvation Dynamics of Coumarin 153 in 1‐Ethyl‐3‐Methylimidazolium Alkylsulfate Ionic Liquids: Dependence on Alkyl Chain Length

Steady‐state and time‐resolved fluorescence behavior of coumarin 153 (C153) is investigated in a series of 1‐ethyl‐3‐methylimidazolium alkylsulfate ([C₂mim][C_nOSO₃]) ionic liquids differing only in the length of the linear alkyl chain (n=4, 6, and 8) in the anion. The aim of the present study is to understand the role of alkyl chain length in solute rotation and solvation dynamics of C153 in these ionic liquids. The blueshift observed in the steady‐state absorption and emission maxima of C153 on going from the C₄OSO₃ to the C₈OSO₃ system indicates increasing nonpolar character of the microenvironment of the solute with increasing length of the alkyl side chain of the anion of the ionic liquids. The average solvation time is also found to increase on changing the substituent from butyl to octyl, and this is attributed to the increase in the bulk viscosity of the ILs. A steady blueshift of the time‐zero maximum of the fluorescence spectrum with increasing alkyl chain length also indicates that the probe molecule experiences a less polar environment in the early part of the dynamics. Rotational dynamics of C153 are also analyzed by using the Stokes–Einstein–Debye (SED), Gierer–Wirtz (GW), and Dote–Kivelson–Schwartz (DKS) theories. Analyses of the results seem to suggest decoupling of the rotational motion of the probe from solvent viscosity.     

Novel Cyclic Sulfonium‐Based Ionic Liquids: Synthesis,Characterization, and Physicochemical Properties

A new series of ionic liquids composed of three cyclic sulfonium cations and four anions has been synthesized and characterized. Their physicochemical properties, including their spectroscopic characteristics, ion cluster behavior, surface properties, phase transitions, thermal stability, density, viscosity, refractive index, tribological properties, ion conductivity, and electrochemical window have been comprehensively studied. Eight of these salts are liquids at room temperature, at which some salts based on [NO₃]^? and [NTf₂]^? ions exhibit organic plastic crystal behaviors, and all the saccharin‐based salts display relatively high refractive indices (1.442–1.594). In addition, some ionic liquids with the [NTf₂]^? ion exhibit peculiar spectroscopic characteristics in FTIR and UV/Vis regions, whilst those salts based on the [DCA]^? ion show lower viscosities (34.2–62.6 mPa s at 20 °C) and much higher conductivities (7.6–17.6 mS cm^?1 at 20 °C) than most traditional 1,3‐dialkylimidazolium salts.     

Charge‐Scaling Effect in Ionic Liquids from the Charge‐Density Analysis of N,N′‐Dimethylimidazolium Methylsulfate

The charge scaling effect in ionic liquids was explored on the basis of experimental and theoretical charge‐density analyses of [C₁MIM][C₁SO₄] employing the quantum theory of atoms in molecules (QTAIM) approach. Integrated QTAIM charges of the experimental (calculated) charge density of the cation and anion resulted in non‐integer values of ±0.90 (±0.87) e. Efficient charge transfer along the bond paths of the hydrogen bonds between the imidazolium ring and the anion was considered as the origin of these reduced charges. In addition, a detailed QTAIM analysis of the bonding situation in the [C₁SO₄]^? anion revealed the presence of negative π_O→σ*_S‐O hyperconjugation.     

Highly Efficient Diglycolamide‐Based Task‐Specific Ionic Liquids: Synthesis,Unusual Extraction Behaviour,Irradiation, and Fluorescence Studies

Two new diglycolamide‐based task‐specific ionic liquids (DGA? TSILs) were evaluated for the extraction of actinides and lanthanides from acidic feed solutions. These DGA? TSILs were capable of exceptionally high extraction of trivalent actinide ions, such as Am³⁺, and even higher extraction of the lanthanide ion, Eu³⁺ (about 5–10 fold). Dilution of the DGA? TSILs in an ionic liquid, C₄mim⁺ ? NTf₂^?, afforded reasonably high extraction ability, faster mass transfer, and more efficient stripping of the metal ion. The nature of the extracted species was studied by slope analysis, which showed that the extracted species contained one NO₃^? anion, along with the participation of two DGA? TSIL molecules. Time‐resolved laser fluorescence spectroscopy (TRLFS) analysis showed a strong complexation with no inner‐sphere water molecule in the Eu^III? DGA? TSIL complexes in the presence and absence of C₄mim⁺ ? NTf₂^? as the diluent. The very high radiolytic stability of DGA? TSIL 6 makes it one of the most‐efficient solvent systems for the extraction of actinides under acidic feed conditions.     

Transport,Electrochemical and Thermophysical Properties of Two N‐Donor‐Functionalised Ionic Liquids

Two N‐donor‐functionalised ionic liquids (ILs), 1‐ethyl‐1,4‐dimethylpiperazinium bis(trifluoromethylsulfonyl)amide ( 1 ) and 1‐(2‐dimethylaminoethyl)‐dimethylethylammonium bis(trifluoromethylsulfonyl)amide ( 2 ), were synthesised and their electrochemical and transport properties measured. The data were compared with the benchmark system, N‐butyl‐N‐methylpyrrolidinium bis(trifluoromethylsulfonyl)amide ( 3 ). Marked differences in thermal and electrochemical stability were observed between the two tertiary‐amine‐functionalised salts and the non‐functionalised benchmark. The former are up to 170 K and 2 V less stable than the structural counterpart lacking a tertiary amine function. The ion self‐diffusion coefficients (D_i) and molar conductivities (Λ) are higher for the IL with an open‐chain cation ( 2 ) than that with a cyclic cation ( 1 ), but less than that with a non‐functionalised, heterocyclic cation ( 3 ). The viscosities (η) show the opposite behaviour. The Walden [Λ∝(1/η)^t] and Stokes–Einstein [D_i/T)∝(1/η)^t] exponents, t, are very similar for the three salts, 0.93–0.98 (±0.05); that is, the self‐diffusion coefficients and conductivity are set by η. The D_i for 1 and 2 are the same, within experimental error, at the same viscosity, whereas Λ for 1 is approximately 13 % higher than that of 2 . The diffusion and molar conductivity data are consistent, with a slope of 0.98±0.05 for a plot of ln(ΛT) against ln(D₊+D_?). The Nernst–Einstein deviation parameters (Δ) are such that the mean of the two like‐ion VCCs is greater than that of the unlike ions. The values of Δ are 0.31, 0.36 and 0.42 for 3 , 1 and 2 , respectively, as is typical for ILs, but there is some subtlety in the ion interactions given 2 has the largest value. The distinct diffusion coefficients (DDC) follow the order ${D{{{\rm d}\hfill \atop - - \hfill}}}$ <${D{{{\rm d}\hfill \atop ++\hfill}}}$ <${D{{{\rm d}\hfill \atop +- \hfill}}}$ , as is common for [Tf₂N]^? salts. The ion motions are not correlated as in an electrolyte solution: instead, there is greater anti‐correlation between the velocities of a given anion and the overall ensemble of anions in comparison to those for the cationic analogue, the anti‐correlation for the velocities of which is in turn greater than that for a given ion and the ensemble of oppositely charged ions, an observation that is due to the requirement for the conservation of momentum in the system. The DDC also show fractional SE behaviour with t～0.95.     

Click Ionic Liquids: A Family of Promising Tunable Solvents and Application in Suzuki–Miyaura Cross‐Coupling

A series of click ionic salts 4 a – 4 n was prepared through click reaction of organic azides with alkyne‐functionalized imidazolium or 2‐methylimidazolium salts, followed by metathesis with lithium bis(trifluoromethanesulfonyl)amide or potassium hexafluorophosphate. All salts were characterized by IR, NMR, TGA, and DSC, and most of them can be classified as ionic liquids. Their steric and electronic properties can be easily tuned and modified through variation of the aromatic or aliphatic substituents at the imidazolium and/or triazolyl rings. The effect of anions and substituents at the two rings on the physicochemical properties was investigated. The charge and orbital distributions based on the optimized structures of cations in the salts were calculated. Reaction of 4 a with PdCl₂ produced mononuclear click complex 4 a‐Pd , the structure of which was confirmed by single‐crystal X‐ray diffraction analysis. Suzuki–Miyaura cross‐coupling shows good catalytic stability and high recyclability in the presence of PdCl₂ in 4 a . TEM and XPS analyses show formation of palladium nanoparticles after the reaction. The palladium NPs in 4 a are immobilized by the synergetic effect of coordination and electrostatic interactions with 1,2,3‐triazolyl and imidazolium, respectively.