AlCl<Subscript>3</Subscript>/amide ionic liquids for electrodeposition of aluminum

AlCl₃/amide (acetamide, propionamide, butyramide) ionic liquids were used as the electrolytes to study the electrodeposition behavior of aluminum on a tungsten electrode. Cyclic voltammograms on the tungsten electrode indicate that Al(III) ions can be reduced to aluminum only within the molar ratio range of 1.1 to 1.5 and the reduction potentials of Al(III) ions strongly depend on the molar ratio of AlCl₃/amide. Raman spectra results reveal that the electroactive specie of AlCl₃/amide ionic liquids is Al₂Cl₇ ^?. Aluminum coatings were prepared at ?0.25 V (vs. Al/Al³⁺) and at 313 K in AlCl₃/amide ionic liquids with the molar ratio of 1.3. The SEM and cross-sectional SEM images show that all the obtained aluminum films are silver-colored, thick, and adherent. The EDS and XRD analysis confirm that the obtained deposits are pure aluminum. The present results can provide a new route for aluminum electrodeposition under ambient conditions.     

Polymerised ionic liquid crystals bearing imidazolium and bipyridinium groups

Novel kinds of polymerised ionic liquid crystals (PILCs) bearing imidazolium and bipyridinium groups were synthesised and characterised in this work. Some bromo-polyesters were synthesised in an esterification chain reaction using 2,3-dibromosuccinyl dichloride, isophthaloyl chloride and 4,4′-biphenol. The polyester imidazolium bromides (PIBs) and polyester dipyridinium bromides (PDBs) were obtained by a quaternisation reaction between the bromo-polyesters, N-methylimidazole and 4-4′-bipyridine, respectively. The polyester imidazolium tetrafluoroborates (PITs) and polyester dipyridinium tetrafluoroborates (PDTs) were synthesised using the corresponding PIBs and PDBs in an anion-exchange reaction. The chemical structures, liquid crystalline properties and molecular weights of these polymers were characterised by multiple experimental techniques. All the PILCs including PIBs, PDBs, PITs and PDTs display smectic A phase on heating and cooling cycles. The liquid-crystalline properties of bromo-polyesters are influenced by the length of flexible spacer and composition of polyester backbones, while those of PILCs are determined by the ionic groups as additional important influent factors. In comparison with those of the mother bromo-polyesters, the d-spacing of PILCs reduced slightly due to Im⁺–Br^?, Dp⁺–Br^?, Im⁺–BF₄^? and Dp⁺–BF₄^? ion pairs in the polymer systems. Monocationic imidazolium salts display weaker interionic and intermolecular interaction, higher mobility and lower viscosity than dicationic dipyridinium salts.     

Hydroformylation of Oct‐1‐ene in Novel Ionic Liquid Crystals

Hydroformylation of oct‐1‐ene leading to nonanal (denoted by n) and 2‐methyloctanal (denoted by iso), in a novel series of caprolactam‐based and common imidazolium‐based ionic liquid crystals (ILCs; see Fig. 1) carried out for the first time (caprolactam=hexahydro‐2H‐azepin‐2‐one) (Scheme). Variation of the chain length (n) of the alkyl substituent (C_n) at the caprolactam cation (CP⁺) from n=12 to 18 caused the n/iso ratios to vary from 1.7 to 2.9. Meanwhile, the TOF (turnover frequency) decreased from 148 to 122 mol mol⁻¹ h⁻¹. Hydroformylation in the imidazolium‐based ILCs revealed that [C₁₆MIm]⋅BF₄ (n/iso 5.2, TOF 969 mol mol⁻¹ h⁻¹) was more favorable than [C₁₆MIm]⋅MsO (n/iso 3.7, TOF 969 mol mol⁻¹ h⁻¹) for the formation of the unbranched aldehyde. Although the n/iso ratio in caprolactam‐based ILCs was lower than that in imidazolium‐based ILCs, the conversions are higher in the former ILCs on the whole. It should be noted that the lamellar mesophase has a strong effect on the regioselectivity and TOF of the hydroformylation. Also, it is evident that the influences of different ILCs on the hydroformylation under the various reaction conditions are greatly different. The identification of the reaction products was established by GC and GC/MS analyses.     

Multi-arm ionic liquid crystals formed by cholesteric mesophase and pyridinium groups

ABSTRACT

A series of novel star-shaped ionic liquid crystals (ILCs) compounds with various counterions (derived from HBF₄, HPF₆, CF₃COOH, d-MH-SO₃H, H₃PO₄, p-Toluenesulfonic acid) were designed and synthesised starting from precursors of pyridines and liquid crystalline monomer cholesteryl 4-bromobutanoate. Inducing various counterions by use of ionic self-assembly due to electrostatic attraction of various ion clusters was one of the most essential factors for intermolecular separation. The chemical structures, liquid crystalline properties, self-assembly behaviour and ionic conductivity of these compounds were researched during multiple experimental techniques. The star-shaped ILCs showed a smectic A (SmA) mesophase. The d-spacing of star-shaped ILCs increased slightly due to the increase volume of anion. The clearing temperatures of the pyridinium salts suggested that the effect of the stabilisation on the SmA structures was in the order H₂PO₄^?>BF₄^?>T_S^?>D-MH-SO₃^?>CF₃COO^?>PF₆^?. All these star-shaped ILCs displayed ionic conductivity in mesophase. It was noted that the conductivity (σ) increased with the increase of the anion size and temperature.     

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.     

Tunable Aryl Alkyl Ionic Liquids with Weakly Coordinating Tetrakis((1,1,1,3,3,3‐hexafluoropropan‐2‐yl)oxy)borate [B(hfip)4] Anions

Weakly coordinating borate or aluminate anions have recently been shown to yield interesting properties of the resulting ionic liquids (ILs). The same is true for large phenyl‐substituted imidazolium cations, which can be tuned by the choice, position, or number of substituents on the aromatic ring. We were therefore interested to combine these aryl alkyl imidazolium cations with the weakly coordinating tetrakis((1,1,1,3,3,3‐hexafluoropropan‐2‐yl)oxy)borate [B(hfip)₄]^? anions to study the physical properties and viscosities of these ionic liquids. Despite the large size and high molecular weight of these readily available ILs, they are liquid at room temperature and show remarkably low glass transition points and relatively high decomposition temperatures.     

Ionic Liquids: Dissecting the Enthalpies of Vaporization

We calculate the heats of vaporisation for imidazolium‐based ionic liquids [C_nmim][NTf₂] with n=1, 2, 4, 6, 8 by means of molecular dynamics (MD) simulations and discuss their behavior with respect to temperature and the alkyl chain length. We use a force field developed recently. The different cohesive energies contributing to the overall heats of vaporisations are discussed in detail. With increasing alkyl chain length, the Coulomb contribution to the heat of vaporisation remains constant at around 80 kJ mol^?1, whereas the van der Waals interaction increases continuously. The calculated increase of about 4.7 kJ mol^?1 per CH₂‐group of the van der Waals contribution in the ionic liquid exactly coincides with the increase in the heats of vaporisation for n‐alcohols and n‐alkanes, respectively. The results support the importance of van der Waals interactions even in systems completely composed of ions.     

Grignard allylic substitution catalyzed by imidazol-2-ylidene- and imidazol-4-ylidene-magnesium complexes

In the presence of a catalytic amount of 1,2-disubstituted or 1,2,3-trisubstituted imidazolium salts, γ-substituted allyl chlorides reacted with alkyl Grignard reagents to undergo substitution reactions in an S_N2′-selective fashion, where the magnesium ate complexes [(N-heterocyclic carbene-MgR₃)⁻(MgX)⁺] of imidazol-2-ylidenes or imidazol-4-ylidenes, generated in situ, were postulated as the active species. It was observed that the reactions with imidazol-4-ylidene catalysts were faster than those with imidazol-2-ylidenes. Enantioselective catalysis using a chiral imidazolium salt was preliminarily investigated.     

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.     

Synthesis and Structure of Ionic Liquids Containing the ­[Al(OC6H4CN)4]– Anion

The synthesis, structure, and physical properties of ionic liquids (IL) bearing the novel [Al(O–C₆H₄–CN)₄]^– ion as counterion to the commonly used [NR₄]⁺, [PR₄]⁺ and imidazolium ions are reported. Both the influence of the alkyl chain length as well as the functionalization with cyano groups is studied. These ILs are easily obtained by reaction of Ag[Al(O–C₆H₄–CN)₄] with the corresponding ammonium, phosphonium, and imidazolium halides. The stability towards electrophilic cations was investigated. All prepared salts have a window for the liquid phase of ca. 200 °C and are thermally stable up to 450 °C. The solid‐state structures reveal only weak cation ··· anion and anion ··· anion interactions in accord with the observed low melting points (glass transition points).     

A fast atom bombardment mass spectrometric study of room-temperature 1-ethyl-3-methylimidazolium chloroaluminate(III) ionic liquids. Evidence for the existence of the decachlorotrialuminate(III) anion

Previous studies of 1-ethyl-3-methylimidazolium chloride–aluminium(III) chloride ([emim]Cl–AlCl₃) ionic liquids have been hampered by significant contamination of these liquids by oxide impurities. Treatment of these liquids with phosgene removes the oxide impurities, and the use of a specially constructed sample inlet system for air-sensitive materials permitted them to be studied by fast atom bombardment mass spectrometry. The ions Cl^?, [Cl₂]^?, [AlCl₄]^?, [Al₂Cl₇]^?, [emim]⁺ and [(emim)₂X]⁺ (X = Cl or AlCl₄) were observed for the basic ionic liquid. In addition, the anion [Al₃Cl₁₀]^? was observed for the acidic composition. Within the mass spectrometer, the hydrolyses of [Al₃Cl₁₀]^? to produce [Al₃C_l8O]^? and of [Al₂Cl₇]^? to produce [Al₂Cl₅O]^? were observed. Comparison of these results with published ¹⁷O NMR data suggests that the primary hydrolysis products in acidic ionic liquids are [Al₃Cl₈O]^? and [Al₂Cl₅O]^? and that the principal secondary hydrolysis product is [Al₂Cl₆(OH)]^?.     

Nuclear magnetic resonance study of aluminum chloride-n-Butylpyridinium chloride melts

High resolution proton and ¹³C-NMR measurements were used to follow the variation of the n-butylpyridinium (BP⁺) cation spectra in BP⁺Cl^?AlCl₃ molten mixtures. The mole fraction of AlCl₃ was varied between 0.45 and 0.60. It was found that chemical shifts and proton coupling constants are significantly affected by the BP⁺-Cl^? and BP⁺ -AlCl^?₄ associations. Analysis of the NMR results shows that in the melts the ionic association into ion pairs is essentially quantitative. Lithium-7 NMR of BPCl-AlCl₃-LiCl melt shows that when the mole-fraction of AlCl₃ is < 0.50 (basic melt) LiCl₂^? ion is formed, while in the acidic melts the Li⁺ ion probably interacts with two AlCl₄^? ions to form LiAl₂Cl^?₈ ion.     

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.     

Effect of cations on polyaniline morphology

Nanostructured polyanilines of different morphologies were prepared by chemical polymerization of aniline with ammonium peroxodisulfate in aqueous HCl using various inorganic and organic chlorides as additives with the aim to determine the effect of cations of the added electrolyte on the morphology, spectroscopic characteristics, and conductivity of formed polyanilines. Chlorides of basic metals: NaCl and CaCl₂ did not show any significant effect while AlCl₃ and organic electrolytes were found to influence the morphology of polyanilines. The effect of organic-electrolyte additives, which actually are ionic liquids, is explained by the organization of their molecules to micellar structures that act as soft templates for emerging polyaniline nanoparticles. The effect of AlCl₃ is ascribed to the transformation of its molecules to [AlCl₄]^? anions.     

Tyrosine‐Based Ionic Liquid Crystals: Switching from a Smectic A to a Columnar Mesophase by Exchange of the Spherical Counterion

Synthetic strategies were developed to prepare l ‐tyrosine‐based ionic liquid crystals with structural variations at the carboxylic and phenolic OH groups as well as the amino functionality. Salt metathesis additionally led to counterion variation. The liquid‐crystalline properties were investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and X‐ray diffraction (WAXS, SAXS). The symmetrical ILC chlorides bearing the same alkyl chain at both the ester and ether but either an acyclic or cyclic guanidinium group displayed enantiotropic SmA₂ mesophases with phase widths of 31–88 K irrespective of the head group. It was particularly the replacement of chloride in the acyclic guanidinium ILC by hexafluorophosphate that induced a phase change from SmA₂ to Col_r. This phase change was attributed to a higher curvature of the interface due to the larger anion, which increased the effective head group cross‐sectional area of the amphiphilic ILC. The unsymmetrical acyclic guanidinium chlorides, bearing a constant C₁₄ ester and variable alkyl chains on the phenolic position, formed enantiotropic SmA₂ phases. The derivative with the largest difference in chain lengths, however, displayed a Col_r phase, resulting from discoid aggregates of the cone‐shaped guanidinium chloride. The results are discussed in terms of the packing parameters, which indicate that the phase behaviour of the thermotropic tyrosine‐based ILCs shows analogies to those of lyotropic liquid crystals.     

Star-shaped supramolecular ionic liquid crystals based on pyridinium salts

Series of novel star-shaped liquid crystals containing [1,1?-biphenyl]-4,4?-diyl diisonicotinate mesogens with various counterions (Br^?, B-SO₃^?,C-SO₃^?,H₂PO₄^?, BF₄^?) have been synthesized and characterized, which display a nematic phase. The molecular structures of the liquid crystals, thereof consisting of rod-like mesogens linked together by different long alkyl spacers to a small disc-like core of central benzene-1,3,5-triyl triisonicotinate, have been fully characterized by ¹H NMR. Their thermal and supramolecular organization behaviours have been studied by combining polarized optical microscopy, differential scanning calorimetry and small-angle X-ray scattering. These investigations showed that the mesophase temperature range increased with increasing alkyl chain length and the clearing point decreased with increase of anion size. These star-shaped liquid crystals have a long and ordered molecular structure, the electron delocalization of the π-π stacking conjugation effect and the electrostatic attraction of ionic make them have good ferroelectric properties and ionic conductivity properties. The interest in preparing ionic liquid crystal with a nematic phase lies in the technological applications as it is well known that the nematic phase has the highest fluidity of all liquid crystalline phases and hence the possibility to align it by applying an external electric/magnetic field, commonly used in electro-optical devices.     

Synthesis and Characterization of 5‐Cyanotetrazolide‐Based Ionic Liquids

New salts based on imidazolium, pyrrolidinium, phosphonium, guanidinium, and ammonium cations together with the 5‐cyanotetrazolide anion [C₂N₅]^? are reported. Depending on the nature of cation–anion interactions, characterized by XRD, the ionic liquids (ILs) have a low viscosity and are liquid at room temperature or have higher melting temperatures. Thermogravimetric analysis, cyclic voltammetry, viscosimetry, and impedance spectroscopy display a thermal stability up to 230 °C, an electrochemical window of 4.5 V, a viscosity of 25 mPa s at 20 °C, and an ionic conductivity of 5.4 mS cm^?1 at 20 °C for the IL 1‐butyl‐1‐methylpyrrolidinium 5‐cyanotetrazolide [BMPyr][C₂N₅]. On the basis of these results, the synthesized compounds are promising electrolytes for lithium‐ion batteries.     

Liquid chromatography and characterization of ether-functionalized imidazolium ionic liquids on mixed-mode reversed-phase/cation exchange stationary phase

A new series [C_nO_mmim]Cl of imidazolium cation-based ionic liquids (ILs), with an ether functional group on the alkyl side-chain, has been prepared. The possibility of analyzing the ionic liquids by high performance liquid chromatography (HPLC) was investigated on mixed-mode reversed/cation exchange stationary phase with the aqueous-acetonitrile mobile phase. Elution parameters, such as retention factor, selectivity and column efficiency, were studied as functions of mobile phase composition and pH. The ILs were characterized by elemental analysis, and infrared, UV and ¹H, ¹³C NMR spectroscopy.     

Direct transition from the SmA phase to the tilted hexatic phase in liquid crystals with several lactate units

Compounds with differing numbers of lactate units in the chiral part were synthesized. For all materials, at least two smectic phases were found. In addition to the SmA, the SmC* and/or the tilted hexatic SmI*(F*) phase appear according to the length of the non-chiral alkyl chain. For the shortest non-chiral chain, a direct transition from the SmA phase to the SmI*(F*) phase has been discovered and studied. For compounds with the 2-(S)-methylbutyl alkyl chain and two lactate units in the chiral part the antiferroelectric SmC*_A phase occurs. The ferroelectric character of the hexatic phase has been confirmed even just below the SmC*_A phase.     

A Novel Room Temperature Ionic Liquid Extraction Spectrophotometric Determination of Trace Germanium in Natural Water with Methybenzeneazosalicylfluorone

Abstract

This paper describes a highly sensitive and selective extraction spectrophotometric method for determination of trace germanium in natural water with new a chromogenic reagent methybenzeneazosalicylfluorone abbreviated as MBASF, in which a typical room temperature ionic liquid, 1‐butyl‐3‐methylimidazolium hexafluorophosphate abbreviated as [C₄mim][PF₆] was used as novel medium for liquid/liquid extraction of germanium(IV). In the presence of TritonX‐100, MBASF reacted with germanium(IV) to form a red complex rapidly, the complex was then extracted into the [C₄mim][PF₆] phase, the absorbance of the complex in ionic liquid at 496 nm was recorded and used to determine trace germanium(IV). The apparent molar absorptivity of the complex and the detection limit for the real sample were found to be 3.12×10⁶ L mol^?1 cm^?1 and 0.2 ng mL^?1, respectively. The absorbance of the complex at 496 nm increases linearly with the concentration up to 4 µg of germanium (IV) in 250 mL of aqueous solution. The interference study show the determination of germanium is free from the interference of almost all positive and negative ions found in the natural water samples. The determination of germanium in natural water was carried out by the present method and electrothermal atomic absorption spectrometry (AAS). The results were satisfactorily comparable so that the applicability of the proposed method was confirmed using the real samples. Moreover, the extraction mechanism with the ionic liquid system was also investigated. We think the extraction performance of the ionic liquid system is a combination of ion‐pairing effect between imidazolium cation and basic solute in the aqueous phase with the dissolution of polar molecule in ionic liquid phase. A wise choice of the appropriate combination of anion with imidazolium cation hydrophobicity allows playing with solute selectivity.