The physicochemical properties of some imidazolium-based ionic liquids and their binary mixtures

The density, viscosity and conductivity of ionic liquids (ILs), 1-octyl-3-methylimidazolium tetrafluoroborate ([omim][BF4]), 1-octyl-3-methylimidazolium chloride ([omim][Cl]), 1-hexyl-3-methylimidazolium tetrafluoroborate ([hmim] BF4]), 1-hexyl- 3-methylimidazolium chloride ([hmim][Cl]), 1-hexyl-3-methylimidazolium hexafluorophosphate ([hmim][PF6]), and the [omim][BF4] + [omim][Cl], [hmim][BF4] + [hmim][Cl], and [hmim][PF6] + [hmim][Cl] binary mixtures were studied at dif- ferent temperatures. It was demonstrated that the densities of both the neat ILs and their mixtures varied linearly with temper- ature. The density sensitivity of a binary mixture is between those of the two components. The excess molar volumes (VE) of [hmim][BF4] + [hmim][Cl] and [hmim][PF6] + [hmim][Cl] mixtures are positive in the whole composition range. For [omim][BF4] + [omim][Cl], the VE is also positive in the [omim][Cl]-rich region, but is negative in the [omim][BF4]-rich re- gion. The viscosity or conductivity of a mixture is in the intermediate of those of the two neat ILs. For all the neat ILs and the binary mixtures studied, the order of conductivity is opposite to that of the viscosity. The Vogel-Tammann-Fulcher (VTF) equations can be used to fit the viscosity and conductivity of all the neat ILs and the binary mixtures. The neat ILs and their mixtures obey the Fractional Walden Rule very well, and the values of the Walden slopes are all smaller than unit, indicating obvious ion associations in the neat ILs and the binary mixtures.     

Palladium‐Catalyzed Enyne Cyclization of 2′‐Alkenyl 2‐Alkynoates in Imidazolium‐Type Ionic Liquids

The use of [bmim][BF₄], [bmim][PF₆], and [bmim][Cl] ILs as the solvents in Pd(II)‐catalyzed enyne cyclization of 2′‐alkenyl 2‐alkynoates in the presence of cupric chloride has been investigated. The Z/E stereoselectivity of the reaction could range from 90:10 to 4:96 by tuning the amount of LiCl in ILs. After the separation of the product, the IL–catalyst mixture could be recovered by treatment with hydrochloric acid and recycled several times without an obvious loss of catalytic activity.     

Structural Aspects of Copper‐Mediated Atom Transfer Radical Polymerization with a Novel Tetradentate Bisguanidine Ligand

This contribution reports the synthesis of the novel tetradentate bisguanidine ligand 2′,2′‐[ethane‐1, 2‐diylbis(methylazanediyl)]bis(ethane‐2, 1‐diyl)bis(1, 1, 3, 3‐tetramethylguanidine) ( L1 , TMG₂dmtrien), which combines two weak amine and two strong guanidine donor functions. Two new copper(II) complexes were isolated and structurally characterized as complexes [Cu(TMG₂dmtrien)][Br]₂ · 3MeCN ( C1 [Br]₂ · 3MeCN) and [Cu(TMG₂dmtrien)][Cl]₂ · 3MeCN ( C2 [Cl]₂ · 3MeCN). The cations C1 and C2 [Cu(TMG₂dmtrien)]²⁺ show a square‐planar coordination environment and are chiral with both enantiomers being observed in the unit cell. We investigated the application of L1 in copper‐mediated styrene ATRP. L1 shows with CuBr and PEBr as initiator a high polymerization activity according to the polymerization rate. First order kinetics confirm the living character of the polymerization. However, the deviation of molecular weights from theoretical molecular weights and the broad molecular weight distributions hint for a low controlled ATRP. The ATRP with further copper(I) salts {CuCl, [Cu(MeCN)₄]BF₄ and [Cu(MeCN)₄]PF₆} and PECl and PEBr as initiators were investigated as well. Herein the use of [Cu(MeCN)₄]PF₆ with PECl led to promising results.     

Isobaric vapor–liquid equilibria for ethanol–water system containing different ionic liquids at atmospheric pressure

Isobaric vapor–liquid equilibrium (VLE) data for ethanol–water systems containing ionic liquids (ILs) 1-methyl-3-methylimidazolium dimethylphosphate ([MMIM][DMP]), 1-ethyl-3-methylimidazolium diethylphosphate ([EMIM][DEP]), 1-butyl-3-methylimidazolium bromide ([BMIM][Br]), 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]) and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF₆]) at atmospheric pressure (101.32 kPa) were measured with a circulation still. The results showed that the VLE of ethanol–water systems in the presence of different ILs was obviously different from that of the IL-free system. All ILs studied showed a salting-out effect, which gave rise to a change of the relative volatility of ethanol, and even to an elimination of the azeotropic point. It was found that the salting-out effect followed the order of [BMIM][Cl] > [BMIM][Br] > [BMIM][PF₆] and [MMIM][DMP] > [EMIM][DEP], which was ascribed to the preferential solvation ability of the ions resulting from the dissociation of the IL.     

Synthesis of TiO2 hollow spheres using binary ionic liquids as an electrocatalyst

Titanium dioxide (TiO₂ titania) hollow sphere was simply synthesized using various ionic liquids (ILs). The shape and size of TiO₂ particles were significantly different with the composition of ILs. This is mainly attributed to the interaction between organic solvent and IL at the interface leading to the formation of sphere. Among the binary ILs, [Bmim][BF₄] + [Omim][PF₆], [Bmim][BF₄] + [Omim][PF₆], and [Bmim][PF₆] + [Hmim][PF₆] were useful to prepare TiO₂ nanostructures with high surface area and anatase phase. Especially, [Bmim][BF₄] + [Omim][PF₆] was the most effective IL to synthesize an anatase TiO₂ hollow sphere.

     

烷基咪唑离子液体对脂肪酶催化酯水解反应活性的影响

考察了1-烷基-3-甲基咪唑类离子液体对柱状假丝酵母脂肪酶(CRL)催化橄榄油水解反应活性的影响,利用电导法确定了磷酸盐缓冲液中Br^-,Cl^-,[BF₄]^-系列咪唑离子液体的临界胶束浓度(CMC)和[PF₆]^-系列咪唑离子液体的溶解度.结果显示,离子液体的阴、阳离子对酶活性的影响规律与离子液体的Kosmotropicity性质无明显关联,但与离子液体在体系中的含量密切相关,在最适离子液体含量时,酶活性达到最高;阳离子[C_nMIM]⁺中的n越大,可促进酶活性的离子液体适宜含量越低;Br^-,[BF₄]^-系列离子液体的浓度超过CMC时则抑制酶活;阴离子对酶活性的最大促进作用顺序为Br^->Cl^->[BF₄]^->[PF₆]^-.离子液体对酶活性的影响随体系pH和温度的不同而改变,在最适离子液体浓度时的最适pH均为7.000.在pH 7.000,30 ^oC以及[C₈MIM]Br离子液体浓度为47.6 mmol/L的最佳条件下,最高相对酶活力和比活力分别达到1734%和54.4 U/mg protein.     

Anion-templated assembly of half-sandwich rhodium-based multinuclear metallamacrocycles

A series of half‐sandwich rhodium‐based metallamacrocycles with tetra‐ and hexanuclearities have been synthesized. They are assembled by linking the deprotonated 2,4‐diacetyl‐5‐hydroxy‐5‐methyl‐3‐(3‐pyridinyl)cyclohexanone (HL) ligand in the presence of counteranions. When the counteranion was the tetrahedral BF₄^? ion, tetranuclear metallamacrocycle [(Cp*RhL)₄][BF₄]₄ ( 1 d ) was formed. However, the larger OTf^?, PF₆^?, and SbF₆^? counterions favored the formation of hexanuclear metallamacrocycles [(Cp*RhL)₆?2OTf][OTf]₄ ( 1 a ), [(Cp*RhL)₆?2PF₆][PF₆]₄ ( 1 b ), and [(Cp*RhL)₆?2SbF₆][SbF₆]₄ ? 6CH₃CN ( 1 c ) when the reactions were performed under the same conditions. Single‐crystal X‐ray analysis indicated that, in the solid state, two counteranions were encapsulated in each belt‐like host molecule of hexanuclear metallamacrocycles 1 a , b , and c . Based on the results of ¹H NMR analysis in methanol, the nuclearities of 1 a – c and the two encapsulated anions in each molecular cavity were maintained in solution. In addition, tetranuclear metallamacrocycle 1 d was converted into the hexanuclear metallamacrocycles 1 a′ , b , and c after addition of the appropriate anion as its [NBu₄]⁺ salt. The compound 1 a′ was characterized by single‐crystal X‐ray diffraction to have the formula [(Cp*RhL)₆?2OTf][BF₄]₄ ? 2M eOH ? 2H₂O. From the interconversion of the hexanuclear metallamacrocycles, we have concluded that the hexanuclear belt‐like host in 1 a – c has an clear selectivity for larger anions, in the sequence SbF₆^?≈PF₆^?>OTf^?>BF₄^?>Cl^?.     

Evaluation of Spectroscopic and Morphological Properties of PMMA Modified with ILs

Summary: In recent years, an important class of new compounds, ionic liquids (ILs), has been investigated as additives for polymers. In this work, we carried out the synthesis of 4 different ILs: 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM.BF₄), 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM.PF₆), and the chiral ILs acetyl-(−)menthol-1-buthylimidazole tetrafluoroborate ([amebim]BF₄) and acetyl-(−)menthol-1-buthylimidazole hexafluorophosphate ([amebim]PF₆). These ILs were added to poly(methyl methacrylate) (PMMA) in 10, 20 and 30% ratios by weight and the ILs, PMMA and the obtained materials (PMMA:ILs) were characterized by infrared, visible spectroscopy and atomic force microscope. The ILs added to PMMA did not provide significant changes in the infrared spectra, compared to pure PMMA. However, the absorption spectra in the visible region of the PMMA:ILs materials showed differences, compared to the spectrum of pure PMMA.     

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.     

Rapid Preparation of Silsesquioxane‐Based Ionic Liquids

Three new hybrid ionic liquids (ILs) based on cage silsesquioxane (SQ) were rapidly prepared in high yields from octa(mercaptopropyl)silsesquioxane and 1‐allyl‐3‐methylimidazolium salts (Br^?, BF₄^?, PF₆^?) through the photochemical thiol–ene reaction. These SQ‐based ILs exhibited low glass transition temperatures and good thermal stability. The unique amphiphilic nature of these hybrid ILs cause them to self‐assemble into perfect vesicles with “yolk–shell” structures, in which cages formed the “yolk” due to their aggregation and outer anions formed the “shell”.     

Tuning the Optical Properties of 2‐Thienylpyridyl Iridium Complexes through Carboranes and Anions

2‐Thienylpyridyl iridium(III) complexes containing an o‐, m‐, or p‐carboranylvinyl‐2,2′‐bipyridine ligand and various counteranions (denoted o ‐ PF₆ , m ‐ BF₄ , m ‐ PF₆ , m ‐ SbF₆ , m ‐ ClO₄ , m ‐ OTf , m ‐ NO₃ , m ‐ BPh₄ , m ‐ F , m ‐ Cl , and p ‐ PF₆ ) were synthesized by using C‐formyl carboranes as starting materials. The solid‐state structures of o ‐ PF₆ , m ‐ PF₆ , m ‐ ClO₄ , and m ‐ BF₄ showed that the cations form twisted cavities in which the anions are fixed by multiple hydrogen bonds. Anion–hydrogen interactions were investigated for nine m‐carborane‐based complexes with different counteranions. All carborane‐based iridium(III) complexes show similar phosphorescence yields in solution but significantly different emission in the solid state. Anion‐exchange titration and theoretical calculations revealed the relationships between structures and optical properties. The size of the anion and C?H ??? X anion–hydrogen bonds strongly influence the phosphorescence quantum yield in the solid state. In particular, the C_car?H ??? X hydrogen bonds between the carboranyl unit and the anion play an important role in solid‐state phosphorescence. Complex p ‐ PF₆ was successfully applied in phosphorescence‐lifetime bioimaging owing to its low toxicity and near‐infrared emission.     

Measurement and Correlation of the Ionic Conductivity of Ionic Liauid-Molecular Solvent Solutions

The ionic conductivity of the solutions formed from 1-n-butyl-3-methylimidazolium tetrafluoroborate （[Bmim][BF4]） or 1-n-butyl-3-methylimidazolium hexafluorophosphate （[Bmim][PF6]） and different molecular solvents （MSs） were measured at 298.15 K. The molar conductivity of the ionic liquids （ILs） increased dramatically with increasing concentration of the MSs. It was found that the molar conductivity of the IL in the solutions studied in this work could be well correlated by the molar conductivity of the neat ILs and the dielectric constant and molar volume of the MSs.     

High-pressure infrared spectroscopy of ionic liquids mixed with Tween 80

In this study, the possibility of using Tween 80 to disturb the microstructures of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF₄) and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF₆) was investigated under high pressures. The imidazolioum C H absorptions of pure ionic liquids (ILs) are significantly blue-shifted under high pressures. However, mild changes in imidazolioum C H stretching frequencies were observed for IL/Tween 80 mixtures. Tween 80 may hinder cations of ILs to form network structures with anions under high pressures via pressure-enhanced cation-Tween 80 interactions. Based on the experimental results, Tween 80-[BMIM]PF₆ interactions are more effective in disturbing the local structure of imidazolium C H than Tween 80-[BMIM]BF₄ interactions.     

Columnar Mesophases Controlled by Counterions in Potassium Complexes of Dibenzo[18]crown‐6 Derivatives

Dibenzo[18]crown‐6 derivatives 1 with two lateral tetraalkyloxy o‐terphenyl units were prepared and converted to the corresponding complexes KX ?1 (X=halide, BF₄, PF₆, SCN) and NH₄PF₆ ?1 . Complexation was probed by MALDI‐TOF spectrometry and NMR spectroscopy. Downfield shifts of ¹H NMR signals for complexes with soft anions Br, I, SCN, and PF₆ indicated the presence of tight ion pairs, whereas complexes with hard anions F, Cl, or BF₄ showed no or little shifts. In ¹³C NMR spectra, upfield shifts were detected for soft anions. The character of the anion also influenced the mesomorphic properties of complexes MX ?1 (M=K, NH₄), which were investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and XRD in comparison to neat 1 . Hard anions slightly stabilize or even destabilize the mesophase. Soft anions, however, improve the mesomorphic properties yielding mesophases with up to 70 °C phase widths in the case of KI ?1 , KPF₆ ?1 , and NH₄PF₆ ?1 . For complexes KSCN ?1 with a soft and bridging anion, the balance between mesophase stabilization and high order is shifted in favor of the plastic crystal phase.     

Ionic Liquid-Induced Structural and Activity Changes in Hen Egg White Lysozyme

Lysozyme crystals in the presence of 1-butyl-3-methylimidazolium tetrafluoroborate ([C₄mim]BF₄), 1-butyl-3-methylimidazolium chloride ([C₄mim]Cl), 1-butyl-3-methylimidazolium bromide([C₄mim]Br), and 1,3-dimethylimidazolium iodine([dmim]I) were prepared, and the influence of ionic liquids (ILs) on the structure and activity change of lysozyme was investigated. Fourier transform infrared spectroscopy revealed the major secondary structures of α-helix and β-sheet for lysozyme. It was interesting to note that increases of the band near 2,935 and 1,656 cm^?1 from Raman spectroscopy are attributed to the unfolding of lysozyme molecules. A shift in amide III from 1,230 to 1,270 cm^?1 in adding [dmim]I occurs, indicating a transformation from β-sheet to random coil. With regard to adding [C₄mim]BF₄, [C₄mim]Cl, and [C₄mim]Br, α-helix and β-sheet are the predominant structures for lysozyme. The activity study showed that the ILs used brought a positive effect. Especially, [dmim]I leads to a drastic increase in relative activity, and its value reaches 50 %.     

Study of novel η-cyclopentadienyl and η-arene platinum group metal complexes containing a N4-type ligand and their structural characterization

The mononuclear η⁵-cyclopentadienyl complexes [(η⁵-C₅H₅)Ru(PPh₃)₂Cl], [(η⁵-C₅H₅)Os(PPh₃)₂Br] and pentamethylcyclopentadienyl complex [(η⁵-C₅Me₅)Ru(PPh₃)₂Cl] react in the presence of 1 eq. of the tetradentate N,N′-chelating ligand 3,5-bis(2-pyridyl)pyrazole (bpp-H) and 1 eq. of NH₄PF₆ in methanol to afford the mononuclear complexes [(η⁵-C₅H₅)Ru(PPh₃)(bpp-H)]PF₆ ([1]PF₆), [(η⁵-C₅H₅)Os(PPh₃)(bpp-H)]PF₆ ([2]PF₆) and [(η⁵-C₅Me₅)Ru(PPh₃)(bpp-H)]PF₆ ([3]PF₆), respectively. The dinuclear η⁵-pentamethylcyclopentadienyl complexes [(η⁵-C₅Me₅)Rh(μ-Cl)Cl]₂ and [(η⁵-C₅Me₅)Ir(μ-Cl)Cl]₂ as well as the dinuclear η⁶-arene ruthenium complexes [(η⁶-C₆H₆)Ru(μ-Cl)Cl]₂ and [(η⁶-p-ⁱPrC₆H₄Me)Ru(μ-Cl)Cl]₂ react with 2 eq. of bpp-H in the presence of NH₄PF₆ or NH₄BF₄ to afford the corresponding mononuclear complexes [(η⁵-C₅Me₅)Rh(bpp-H)Cl]PF₆ ([4]PF₆), [(η⁵-C₅Me₅)Ir(bpp-H)Cl]PF₆ ([5]PF₆), [(η⁶-C₆H₆)Ru(bpp-H)Cl]BF₄ ([6]BF₄) and [(η⁶-p-ⁱPrC₆H₄Me)Ru(bpp-H)Cl]BF₄ ([7]BF₄). However, in the presence of 1 eq. of bpp-H and NH₄BF₄ the reaction with the same η⁶-arene ruthenium complexes affords the dinuclear salts [(η⁶-C₆H₆)₂Ru₂(bpp)Cl₂]BF₄ ([8]BF₄) and [(η⁶-p-ⁱPrC₆H₄Me)₂Ru₂(bpp)Cl₂]BF₄ ([9]BF₄), respectively. These compounds have been characterized by IR, NMR and mass spectrometry, as well as by elemental analysis. The molecular structures of [1]PF₆, [5]PF₆ and [8]BF₄ have been established by single crystal X-ray diffraction studies and some representative complexes have been studied by UV–vis spectroscopy.     

Catalytic activity and recyclability of new enantioselective chiral Co-salen complexes in the hydrolytic kinetic resolution of epichlorohydrine

Chiral Co(III) salen catalysts bearing PF₆, BF₄ or Br counterions proved to be reactive and enantioselective in the hydrolytic resolution of terminal epoxides. The catalysts could be recovered and reused several times without further treatment after reaction, showing no loss of activity and enantioselectivity.     

Cationic ring-opening polymerization of 3,3-bis（chloromethyl）oxacyclobutane in ionic liquids

Cationic ring-opening polymerization of 3,3-bis(chloromethyl)oxacyclobutane catalyzed by BF_3·OEt_2 was carried out in ionic liquids [bmim]BF_4 and [bmim]PF_6.The influences of BCMO concentration and molar ratio of BCMO/BF_3·OEt_2 on the molecular weights and yield of PBCMO were investigated.The polymerization in ionic liquids proceed to high conversions,although molecular weights are limited,similar to polymerization in organic solvent such as CH_2Cl_2.Follow a viewpoint of green chemistry, we feel ionic liquid [bmim]BF_4 is superior to [bmim]PF_6.Extracting [bmim]PF_6 from the product using organic solvent as extractant limits its advantage as a green reaction media.     

The Synthesis of Anatase TiO2 Nanoparticles by Solvothermal Method using Ionic Liquid as Additive

The solvothermal reactions of Ti(OiPr)₄ in alcohol using ionic liquid as additive were investigated. In the presence of [BMIM][Cl], [BMIM][Br], [BMIM][NTf₂], [BMIM][SO₃Me], [BMIM][SO₄Me], or [BMIM][OTf] (BMIM = 1‐Butyl‐3‐methylimidazolium), pure anatase nanoparticles were obtained. The controlled hydrolysis of Ti(OiPr)₄ in the presence of ionic liquids to form titanium oxo clusters plays a key role in the formation of anatase nanostructures, and ionic liquids can be repeatedly used to synthesise anatase nanoparticles. However, in the presence of [BMIM][PF₆], [BMIM]₂[Ti(OH)₆] was obtained by an anion exchange reaction.