Imidazolium‐based polymerized ionic liquid crystals containing fluorinated cholesteryl mesogens

A series of polymerized ionic liquid crystals (PILCs) bearing fluorinated cholesteryl mesogens were synthesized in this work, which include polymerized imidazolium bromides (PIBs) and polymerized imidazolium hexafluorophosphates (PIHs). The PIBs were synthesized using alkyl bromine‐containing polysiloxanes and 1‐butyl‐1H‐imidazole, and the PIHs were synthesized by anion metathesis reaction using the corresponding PIBs and KPF₆. The chemical structures, liquid crystalline (LC) properties, and electrorheological (ER) effect of these PILCs were characterized by use of various experimental techniques. All the PILCs showed smectic A mesophase on heating and cooling cycles. The smectic layer structure of these PILCs are originated from the rigid fluorinated cholesteryl mesogens and the flexible moieties in the LC phase, but the ion pairs (imidazolium cations–PF₆^?, Im⁺–PF₆^?; or imidazolium cations–Br^?, Im⁺–Br^?) can disperse in the polysiloxane matrix and expand the d‐spacing in the smectic layers. The PIHs show lower T_g and T_i than the corresponding precursor PIBs, which is due to the larger ion volume of Im⁺–PF₆^? for PIHs than that of Im⁺–Br^? for PIBs. A series of 40 V% ER fluids were prepared by mixing the PILCs with polydimethylsiloxane (PDMS), and the ER behaviors were studied. All the PILC/PDMS fluids showed ER effect, and the PIH/PDMS fluids show a little greater ER effect than the PIB/PDMS fluids. The PILC droplets in the ER fluids become deformed owing to both the orientation of fluorinated cholesteryl mesogens and the suppression of ionic migration when a DC electric field was applied, resulting in the occurrence of ER effect. Copyright © 2015 John Wiley & Sons, Ltd.     

Raman Spectroscopic Study on Alkyl Chain Conformation in 1‐Butyl‐3‐methylimidazolium Ionic Liquids and their Aqueous Mixtures

Ionic liquids of 1‐butyl‐3‐methylimidazolium ([BMIM]) cation with different anions (Cl^?, Br^?, I^?, and BF₄^?), and their aqueous mixtures were investigated by using Raman spectroscopy and dispersion‐included density functional theory (DFT). The characteristic Raman bands at 600 and 624 cm^?1 for two isomers of the butyl chain in the imidazolium cation showed significant changes in intensity for different anions as well as in aqueous solutions. The area ratio of these two bands followed the order I^?>Br^?>Cl^?>BF₄^? (in terms of the anion X in [BMIM]X), indicating that the butyl chain of [BMIM]I tends to adopt the trans conformation. The butyl chain was found to adopt the gauche conformation upon dilution, irrespective of the anion type. The Raman bands in the butyl C?H stretch region for [BMIM]X (X=Cl^?, Br^?, and I^?) blueshifted significantly with the increase in the water concentration, whereas that for [BMIM]BF₄ changed very little upon dilution. The blueshift in the C?H stretch region upon dilution also followed the order: [BMIM]I>[BMIM]Br>[BMIM]Cl>[BMIM]BF₄, the same order as the above trans conformation preference of the butyl chain in pure imidazolium ionic liquids, which suggested that the cation‐anion interaction plays a role in determining the conformation of the chain.     

Theoretical study of interactions between 1-alkyl-3-methyimidazolium tetrafluoroborate and dibenzothiophene: DFT,NBO, and AIM analysis

Density functional theory is employed to study the interaction energies between dibenzothiophene (DBT) and 1-alkyl-3-methylimidazolium tetrafluoroborate ([C _n mim]⁺[BF₄]^?). The structures of DBT, 1-ethyl-3-methylimidazolium tetrafluoroborate ([C₂mim]⁺[BF₄]^?), 1-butyl-3-methylimidazolium tetrafluoroborate ([C4mim]+[BF₄]?), 1-hexyl-3-methylimidazolium tetrafluoroborate ([C₆mim]⁺[BF₄]^?), 1-octyl-3-methylimidazolium tetrafluoroborate ([C₈mim]⁺[BF₄]^?), [C₂mim]⁺[BF₄]^?–DBT, [C₄mim]⁺[BF₄]^?–DBT, [C₆mim]⁺[BF₄]^?–DBT and [C₈mim]⁺[BF₄]^?–DBT systems are optimized systematically at the B3LYP/6-31G(d,p) level, and the most stable geometries are obtained by NBO and AIM analyses. The results indicate that DBT and imidazolium rings of ionic liquids are parallel to each other. It is found that the [BF₄]^? anion prefers to be located close to a C1–H9 proton ring in the vicinity of the imidazolium ring and the most stable gas-phase structure of [C _n mim]⁺[BF₄]^? has four hydrogen bonds between [C _n mim]+ and [BF₄]?. There are hydrogen bonding interactions, π–π and C–H–π interactions between [C₈mim]⁺[BF₄]^? and DBT, which is confirmed by NBO and AIM analyses. The calculated interaction energies for the studied ionic liquids can be used to interpret a better extracting ability of [C₈mim]⁺[BF₄]^? to remove DBT, due to stronger interactions between [C₈mim]⁺[BF₄]^? and DBT, in agreement with the experimental results of dibenzothiophene extraction by [C _n mim]⁺[BF₄]^?.     

A Rapid and Efficient Stereoselective Synthesis of (Z)‐ and (E)‐Allyl Bromides from Baylis–Hillman Adducts Using Bromo(dimethyl)sulfonium Bromide

Treatment of Baylis–Hillman adducts 1 with bromo(dimethyl)sulfonium bromide, Br(Me₂)S⁺Br^?, in MeCN was found to stereoselectively afford (Z)‐ and (E)‐allyl bromides 2 . The reaction is rapid at room temperature, high‐yielding, and highly stereoselective.     

Effect of counter-ion on the thermotropic liquid crystal behaviour of bis(alkyl)-tris(imidazolium salt) compounds

Recently, new thermotropic ionic liquid crystals (LCs) with a hexyl-linked tris(imidazolium bromide) core and two terminal alkyl chains were synthesised and characterised. To explore the effect of different counter-ions on the LC behaviour of this system, derivatives with BF₄^? and Tf₂N^? counter-ions were prepared and analysed. Five of the BF₄^? derivatives were found to exhibit thermotropic LC behaviour. The 12-, 14- and 16-carbon tail BF₄^? compounds form SmA phases. The 18- and 20-carbon tail homologues form what appears to be a smectic phase but are weakly mesogenic and harder to characterise. Only two of the Tf₂N^? derivatives exhibited mesogenic behaviour. The 18-carbon tail Tf₂N^? compound forms an as-yet unidentified, highly periodic smectic phase with positional order while the 20-carbon tail homologue forms a periodic SmA phase. The Tf₂N^? mesogens have much lower clearing points even though their LC phases have more order than the Br^? and BF₄^? mesogens. X-ray diffraction showed that these mesogens have different amounts of tail interdigitation between the smectic layers depending on the counter-ion present. Atomistic molecular dynamics simulations indicated that counter-ion size plays an important role in defining the density of the ionic region, which in turn affects the amount of interdigitation in the smectic phases.     

Use of Ionic liquids as additives in ion exchange chromatography for the analysis of cations

The behavior of acids (citric acid, nitric acid, oxalic acid, tartaric acid) as a mobile phase and imidazolium ionic liquids (the bromides, tetrafluoroborates and hexafluorophosphates of 1‐ethyl, 1‐butyl, and 1‐hexyl‐3‐methylimidazolium) as additives in ion exchange chromatography for cations (Na⁺, K⁺, Mg²⁺, Ca²⁺) separation were studied. The results showed that nitric acid and 1‐hexyl‐3‐methyl‐imidazolium hexafluorophosphate offered the most interesting features in the separation of cations, such as lower retention time and better resolution. The selected optimal conditions were achieved by adding 0.10 mM 1‐hexyl‐3‐methyl‐imidazolium hexafluorophosphate in 4.0 mM HNO₃ mobile phase for the separation of four cations with the flow rate of 0.9 mL/min at room temperature (25°C). The linear regression equations of Na⁺, K⁺, Mg²⁺, Ca²⁺ were S  = 4.4763c  + 0.0209, S  = 3.8903c  – 0.0087, S  = 6.3974c  – 0.0173, and S  = 7.601c  – 0.0339 and the limits of detection of Na⁺, K⁺, Mg²⁺, Ca²⁺ were 0.296, 4.98, 0.0970, and 1.22 μg/L, respectively. In this work, four cations in samples were successfully detected.     

Synthesis and characterization of anhydrous conducting polyimide/ionic liquid complex membranes via a new route for high‐temperature fuel cells

The paper deals with the synthesis and characterization of a new series of anhydrous conducting acid‐doped complex membranes based on polyimide (PI) and ionic liquid (IL) for high‐temperature fuel cells via a new route. For this purpose, three imidazolium‐based ILs (RIm⁺BF₄^?) with different alkyl chain lengths (R=methyl, ethyl, and butyl) are added into polyamic acid (PAA) intermediate prepared from the reaction of benzophenonetetracarboxylic dianhydride and diaminodiphenylsulfone in different –COOH/imidazolium molar ratios (n = 0.5, 1, and 2). Then, the thermally imidized complex membrane was doped with H₂SO₄. The conductivities of acid‐doped PI/IL complex membranes prepared by taking n of 1 are found to be in the range of 10^?4?10^?5 S cm^?1 at 180°C, whereas the acid‐free PI/IL complex membranes show the conductivity at around 10^?9?10^?10 S cm^?1. Thermogravimetric analysis results reveal that the acid‐doped PI/IL complex membranes are thermally stable up to 250°C. Dynamic mechanical analysis results of the acid‐doped ionically interacted complex membrane show that the mechanical strengths of the PI/IL complex membranes including 1‐methyl imidazolium tetrafluoroborate (MeIm‐BF₄) and 1‐ethyl 3‐methyl imidazolium tetrafluoroborate (EtIm‐BF₄) are comparable with those of pristine PI until 200°C. Furthermore, it can be clearly emphasized that the ionic interaction between carboxylic acid groups of PAA's and IL's cations offers a positive role in long‐term conductivity stability by preventing the IL migration at high temperatures. On the other hand, preliminary methanol permeability tests of the acid‐doped membranes show that they can also be considered as an alternative for direct methanol fuel cells. Copyright © 2011 John Wiley & Sons, Ltd.     

Ionic Association of the Ionic Liquids [C4mim][BF4], [C4mim][PF6], and [Cnmim]Br in Molecular Solvents

Considering the ionic nature of ionic liquids (ILs), ionic association is expected to be essential in solutions of ILs and to have an important influence on their applications. Although numerous studies have been reported for the ionic association behavior of ILs in solution, quantitative results are quite scarce. Herein, the conductivities of the ILs [C_nmim]Br (n=4, 6, 8, 10, 12), [C₄mim][BF₄], and [C₄mim][PF₆] in various molecular solvents (water, methanol, 1‐propanol, 1‐pentanol, acetonitrile, and acetone) are determined at 298.15 K as a function of IL concentration. The conductance data are analyzed by the Lee–Wheaton conductivity equation in terms of the ionic association constant (K_A) and the limiting molar conductance (Λ_m⁰). Combined with the values for the Br^? anion reported in the literature, the limiting molar conductivities and the transference numbers of the cations and [BF₄]^? and [PF₆]^? anions are calculated in the molecular solvents. It is shown that the alkyl chain length of the cations and type of anion affect the ionic association constants and limiting molar conductivities of the ILs. For a given anion (Br^?), the Λ_m⁰ values decrease with increasing alkyl chain length of the cations in all the molecular solvents, whereas the K_A values of the ILs decrease in organic solvents but increase in water as the alkyl chain length of the cations increases. For the [C₄mim]⁺ cation, the limiting molar conductivities of the ILs decrease in the order Br^?>[BF₄]^?>[PF₆]^?, and their ionic association constants follow the order [BF₄]^?>[PF₆]^?>Br^? in water, acetone, and acetonitrile. Furthermore, and similar to the classical electrolytes, a linear relationship is observed between ln K_A of the ILs and the reciprocal of the dielectric constants of the molecular solvents. The ILs are solvated to a different extent by the molecular solvents, and ionic association is affected significantly by ionic solvation. This information is expected to be useful for the modulation of the IL conductance by the alkyl chain length of the cations, type of anion, and physical properties of the molecular solvents.     

Template‐free anion‐controlled synthesis of Pd (II) nano‐aggregates for the antifouling polymerization of CO and ethylene

The reaction of [(domppp) Pd (OAc)₂] [domppp = 1,3‐bis (di‐o‐methoxyphenylphosphino)propane] and imidazolium‐functionalized carboxylic acids containing various anions (Br^?, PF₆^?, SbF₆^? and BF₄^?) resulted in the formation of nano‐sized Pd (II) aggregates under template‐free conditions. The rate of formation of aggregates can be modulated by changing the anion, affecting the rate of polymerization of CO and olefins without fouling. Herein, we describe the analysis of Pd (II) catalysts by dynamic light scattering, atomic force microscopy, X‐ray photoelectron spectroscopy and X‐ray crystallography, and co‐ and terpolymerization results including the catalytic activity, and bulk density and molecular weight of polymers.     

Effect of imidazolium salts on the catalytic reaction of 1,3-dioxolanes with methyl diazoacetate

Effect of imidazolium salts, [bmim]⁺Cl^?, [bmim]⁺BF₄ ^?, and [bmim]⁺PF₆ ^?, on the reaction of 1,3-dioxolanes with methyl diazoacetate in the presence of copper-containing catalysts was studied. The product composition was found to depend on the reaction conditions and the nature and ratio of components of the catalytic system.     

Mechanism of Dissolution of a Lithium Salt in an Electrolytic Solvent in a Lithium Ion Secondary Battery: A Direct Ab Initio Molecular Dynamics (AIMD) Study

The mechanism of dissolution of the Li⁺ ion in an electrolytic solvent is investigated by the direct ab initio molecular dynamics (AIMD) method. Lithium fluoroborate (Li⁺BF₄^?) and ethylene carbonate (EC) are examined as the origin of the Li⁺ ion and the solvent molecule, respectively. This salt is widely utilized as the electrolyte in the lithium ion secondary battery. The binding of EC to the Li⁺ moiety of the Li⁺BF₄^? salt is exothermic, and the binding energies at the CAM–B3LYP/6‐311++G(d,p) level for n=1, 2, 3, and 4, where n is the number of EC molecules binding to the Li⁺ ion, (EC)_n(Li⁺BF₄^?), are calculated to be 91.5, 89.8, 87.2, and 84.0 kcal mol^?1 (per EC molecule), respectively. The intermolecular distances between Li⁺ and the F atom of BF₄^? are elongated: 1.773 Å (n=0), 1.820 Å (n=1), 1.974 Å (n=2), 1.942 Å (n=3), and 4.156 Å (n=4). The atomic bond populations between Li⁺ and the F atom for n=0, 1, 2, 3, and 4 are 0.202, 0.186, 0.150, 0.038, and 0.0, respectively. These results indicate that the interaction of Li⁺ with BF₄^? becomes weaker as the number of EC molecules is increased. The direct AIMD calculation for n=4 shows that EC reacts spontaneously with (EC)₃(Li⁺BF₄^?) and the Li⁺ ion is stripped from the salt. The following substitution reaction takes place: EC+(EC)₃(Li⁺BF₄^?)→(EC)₄Li⁺?(BF₄^?). The reaction mechanism is discussed on the basis of the theoretical results.     

Theoretical study on interactions between thiophene/dibenzothiophene/cyclohexane/toluene and 1-methyl-3-octylimidazolium tetrafluoroborate

It is critically important to understand the interactions between thiophene/dibenzothiophene/cyclohexane/toluene and 1-methyl-3-octylimidazolium tetrafluoroborate ([C8MIM]⁺[BF₄]^?) due to desulfurization by ionic liquids. In this work, the structures of thiophene, dibenzothiophene, cyclohexane, toluene, [C8MIM]⁺[BF₄]^?, [C8MIM]⁺[BF₄]^?-thiophene, [C8MIM]⁺[BF₄]^?-dibenzothiophene, [C8MIM]⁺[BF₄]^?-cyclohexane, and [C8MIM]⁺[BF₄]^?-toluene were optimized systematically at the GGA/PW91/DNP level, and the most stable geometries were performed by NBO and AIM analyses. It was found that [BF₄]^? anion tends to locate near C2–H2 and four hydrogen bonds between [C8MIM]⁺ and [BF₄]^? form in [C8MIM]⁺[BF₄]^?. There exist hydrogen bonds and C–H···π interactions between [C8MIM]⁺[BF₄]^? and thiophene/cyclohexane/toluene, while the hydrogen bonding interactions, π···π and C–H···π interactions occur between [C8MIM]⁺[BF₄]^? and dibenzothiophene confirmed by NBO and AIM analyses. The interaction energies between [C8MIM]⁺[BF₄]^? and thiophene, dibenzothiophene, cyclohexane, toluene are 18.83, 20.93, 6.83, 12.99 kcal/mol, showing the preferential adsorption of dibenzothiophene and thiophene by ionic liquid, in agreement with the experimental results of dibenzothiophene and thiophene extraction by [C8MIM]⁺[BF₄]^?.     

Ion‐Pairing of Phosphonium Salts in Solution: C?H⋅⋅⋅Halogen and C?H⋅⋅⋅π Hydrogen Bonds

The ¹H NMR chemical shifts of the C(α)? H protons of arylmethyl triphenylphosphonium ions in CD₂Cl₂ solution strongly depend on the counteranions X^?. The values for the benzhydryl derivatives Ph₂CH? PPh₃⁺ X^?, for example, range from δ_H=8.25 (X^?=Cl^?) over 6.23 (X^?=BF₄^?) to 5.72 ppm (X^?=BPh₄^?). Similar, albeit weaker, counterion‐induced shifts are observed for the ortho‐protons of all aryl groups. Concentration‐dependent NMR studies show that the large shifts result from the deshielding of the protons by the anions, which decreases in the order Cl^? > Br^? ? BF₄^? > SbF₆^?. For the less bulky derivatives PhCH₂? PPh₃⁺ X^?, we also find C? H???Ph interactions between C(α)? H and a phenyl group of the BPh₄^? anion, which result in upfield NMR chemical shifts of the C(α)? H protons. These interactions could also be observed in crystals of (p‐CF₃‐C₆H₄)CH₂? PPh₃⁺ BPh₄^?. However, the dominant effects causing the counterion‐induced shifts in the NMR spectra are the C? H???X^? hydrogen bonds between the phosphonium ion and anions, in particular Cl^? or Br^?. This observation contradicts earlier interpretations which assigned these shifts predominantly to the ring current of the BPh₄^? anions. The concentration dependence of the ¹H NMR chemical shifts allowed us to determine the dissociation constants of the phosphonium salts in CD₂Cl₂ solution. The cation–anion interactions increase with the acidity of the C(α)? H protons and the basicity of the anion. The existence of C? H???X^? hydrogen bonds between the cations and anions is confirmed by quantum chemical calculations of the ion pair structures, as well as by X‐ray analyses of the crystals. The IR spectra of the Cl^? and Br^? salts in CD₂Cl₂ solution show strong red‐shifts of the C? H stretch bands. The C? H stretch bands of the tetrafluoroborate salt PhCH₂? PPh₃⁺ BF₄^? in CD₂Cl₂, however, show a blue‐shift compared to the corresponding BPh₄^? salt.     

Facile preparation of organic-inorganic hybrid polymeric ionic liquid monolithic column with a one-pot process for protein separation in capillary electrochromatography

An organic-inorganic hybrid monolithic column based on 1-vinyl-3-dodecylimidazolium bromide (VC₁₂Im⁺Br^?) has been prepared in a single step by combining radical copolymerization with a non-hydrolytic sol-gel (NHSG) process. The NHSG process was significantly shortened to 6 h by using formic acid as catalyst. For comparison, we also prepared polymeric ionic liquid (PIL) monolithic columns by hydrolytic sol-gel and organic polymeric process, respectively. The resulting monolithic columns were characterized by Fourier transform infrared spectra, scanning electron microscopy, and Brunauer-Emmett-Teller. Under the capillary electrochromatography mode, these columns were applied to separate alkylbenzenes, anilines, and proteins, respectively. The results indicated that the NHSG-based hybrid PIL monolithic column exhibited the highest column efficiency among the three types of columns; organic solvent, commonly required by the traditional columns to achieve satisfactory separation efficiency for proteins, was absent in the NHSG-based hybrid PIL monolithic column because of the biocompatibility of the VC₁₂Im⁺Br^?, which was beneficial to analysis of protein containing samples. In order to demonstrate its application potential, the developed NHSG-based hybrid PIL monolithic column was also employed to separate egg white sample.     

Nuclear magnetic resonance spectroscopic study on ionic liquids of 1-alkyl-3-methylimidazolium salts

Chemical shifts of ¹H and ¹³C NMR of series of methylimidazolium salts (MIM⁺, X=Br⁻, BF₄⁻ and PF₆⁻) function on the length of alkyl groups on the ring, type of solvents and the concentration. The bromides series demonstrate more chemical shift variation on H2 upon the change of solvents and concentration. Unexpected H-D exchange reactions were also observed in the MIM⁺Br⁻ by using CD₃OD and D₂O. The exchange rates strongly depend on the length of the alkyl group, which could cause more steric factor to reduce the interaction between deuterium atom from solvent and C2 of the ring.     

Two Distinct Thermal Stabilities of DNA and Enzymatic Activities of DNase I in a Multistep Assembly with Carbazole Ligands: Different Binding Characteristics for Duplex and Quadruplex DNA

A partially hydrophobic carbazole ligand ((Im⁺)₂Cz: 2,2′‐(9‐ethyl‐9 H‐carbazole‐3,6‐diyl)bis(ethyne‐2,1‐diyl)bis(1,3‐dimethyl‐1 H‐imidazol‐3‐ium)) adopts two different binding states (binding states I and II) in its interactions with calf‐thymus (ct‐) DNA. Two distinct binding states were identified by biphasic UV/Vis and circular dichroism (CD) spectral changes during the titration of DNA into the carbazole ligand. At low concentrations of ct‐DNA, (Im⁺)₂Cz binds to nearly every part of ct‐DNA (binding state I). By contrast, an increased concentration of ct‐DNA results in a switch in the DNA‐binding state, so that the ligands are bound per five DNA base pairs. Similarly, a monocationic carbazole ligand (Im⁺Cz: 2‐((6‐bromo‐9‐ethyl‐9 H‐carbazol‐3‐yl)ethynyl)‐1,3‐dimethyl‐1 H‐imidazol‐3‐ium) also shows biphasic UV/Vis spectral changes during the titration of ct‐DNA into Im⁺Cz, which suggests two different binding states of the Im⁺Cz ligand with ct‐DNA. The stepwise equilibrium of the ligand–DNA‐complex formation is capable of switching the thermal stability of ct‐DNA, as well as the enzymatic activity of deoxyribonuclease (DNase I). In binding state I, the (Im⁺)₂Cz ligands interact with nearly every base pair in ct‐DNA and stabilize the double‐helix structure, which results in a larger increase in the melting temperature of the ct‐DNA than that observed with binding state II. On the other hand, the (Im⁺)₂Cz ligand significantly reduces the enzymatic activity of DNase I in binding state I, although the enzymatic activity is recovered once the binding state of the ligand–DNA complex is changed to binding state II. The (Im⁺)₂Cz ligand was also employed as a binder for G‐quadruplex DNA. In contrast to the stepwise complex formation between (Im⁺)₂Cz and ct‐DNA, (Im⁺)₂Cz shows a monotonous UV/Vis spectral response during the titration of G‐quadruplex DNA into (Im⁺)₂Cz, which suggests a single binding state for (Im⁺)₂Cz with G‐quadruplex DNA.     

Synthesis and evaluation of neutral anion receptors based on acylhydrazide-appended calix[4]arenes

A new class of neutral receptors based upon acylhydrazide-appended calix[4]arenes was synthesised and evaluated for recognition of anions. Detailed NMR and single-crystal X-ray analyses of one of the synthesised compounds reveal that anion recognition in such derivatives is achieved through cooperative hydrogen bond interactions. The presence of three centred NH–O and two OH–O hydrogen bonds at the lower rim of the synthesised calixarene architecture apparently helps the molecular scaffold to retain cone conformation to enable deployment of intermolecular hydrogen bonds for selective recognition of HSO₄ ^? ion in preference to F^?, Cl^?, Br^?, I^?, ClO₄ ^?, AcO^? and PF₆ ^? ions.     

Thermodynamic study on the interaction of imidazolium salts and POE-type nonionic surfactant in the adsorbed film

The composition of the adsorbed film and the excess Gibbs energy of adsorption $ {\widehat{g}}^{\mathrm{H},\mathrm{E}} $ were evaluated from thermodynamic analysis of surface tensions for the 1-decyl-3-methylimidazoulium bromide (C₁₀mimBr)–tetraethylene glycol monooctyl ether (C₈E₄) and 1-decyl-3-methyl-imidazolium tetrafluorobrorate (C₁₀mimBF₄)–C₈E₄ systems, where the counter anion of imidazolium salts is different from each other. The higher miscibility of two components compared to an ideal mixing and thus negative $ {\widehat{g}}^{\mathrm{H},\mathrm{E}} $ were observed in the former, which comes from the ion–dipole interaction between imidazolium cation and the oxyethylene group of C₈E₄. On the other hand, the lower miscibility and thus positive $ {\widehat{g}}^{\mathrm{H},\mathrm{E}} $ were observed for the latter. Such differences were attributed to that BF₄ ^? forms two hydrogen bonds and has stronger affinity with the cationic head group of C₁₀mim⁺ than Br^?. This results in that the ion–dipole interaction between C₈E₄ and C₁₀mim⁺ cation is diminished in the C₁₀mimBF₄–C₈E₄ system.     

Solvation environment of lithium ion in a LiBF<Subscript>4</Subscript>–propylene carbonate system in the presence of 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid studied by NMR and quantum chemical modeling

Solutions of lithium and 1-ethyl-3-methylimidazolium tetrafluoroborates ([emim][BF₄]) in propylene carbonate (PC) were studied by the high-resolution NMR method on ¹H, ⁷Li, ¹¹B, ¹³C, and ¹⁹F nuclei. The degree of solvation of lithium ions was determined by measuring selfdiffusion coefficients by pulse-field-gradient spin echo NMR method on ¹H, ⁷Li, and ¹⁹F nuclei. The hydrodynamic radii of solvated Li⁺ cations were estimated by the Stokes–Einstein equation. The model structures of the solvation complexes of Li⁺ ion with propylene carbonate molecules and BF ₄ ^– anion and their associates with ionic liquid components were calculated in terms of the density function theory. The calculated values of the chemical shifts were compared with the experimental data. PC molecules were predominantly bound to the Li⁺ cation, while LiBF₄–[emim][BF₄]–PC (1: 4: 4) electrolyte had a maximum conductivity of 9.5 mS cm^–1 at 24 °С compared to the compositions of a lower content of the solvent.     

Study on surface adsorption from cationic surfactant–electrolyte mixed aqueous solution including BF 4 − ion

The surface tension of aqueous mixtures of dodecyltrimethylammonium tetrafluoroborate (DTABF₄) and sodium tetrafluoroborate (NaBF₄) was measured as a function of total molality and composition of DTABF₄ at 298.15 K. The results were analyzed by originally developed thermodynamic equations and compared with those of dodecyltrimethylammonium bromide (DTAB)–sodium bromide (NaBr) mixed system. It was indicated that BF₄⁻ ions reduce the repulsion between DTA⁺ ions more effectively than Br⁻ ions in the adsorbed film. To investigate this difference more closely, the surface tension of DTAB–NaBF₄ and DTABF₄–NaBr mixed system was also measured. The data analysis revealed that BF₄⁻ ions are adsorbed positively even for the pure NaBF₄ system and preferentially to Br⁻ ions in these mixtures. Furthermore, it was concluded that the side-by-side arrangement suggested in the adsorbed film of 1-hexyl-3-methylimidazolium tetrafluoroborate (HMIMBF₄) is due to not only the positive adsorption of BF₄⁻ ions but also the capability of hydrogen bond formation between imidazolium ion and BF₄⁻ ions.