Imidazolium ionic liquid crystals with pendant mesogenic groups

Ionic liquid crystals were obtained by coupling one or two mesogenic units (cholesterol or cyanobiphenyl) to an imidazolium cation. Anions are bromide, bis(trifluoromethylsulfonyl)imide, and tetrakis(2-thenoyltrifluoroacetonato)europate(III). The mesomorphism of the compounds depends on the type and number of mesogenic units and on the type of anion. In general, the most stable mesophases are observed for the bis(trifluoromethylsulfonyl)imide salts. Most of the compounds containing cholesterol moieties show enantiotropic SmA* phases over a broad temperature range, and some of them are room temperature liquid crystals. Modeling of the small-angle X-ray scattering patterns revealed the molecular arrangement in these mesophases. On the contrary, most of the compounds containing cyanobiphenyl groups exhibit monotropic lamellar or nematic mesophases, depending on the number of mesogenic units. The imidazolium salts containing the tetrakis(2-thenoyltrifluoroacetonato)europate(III) anion show an intense red photoluminescence.

Pyrrolidinium Ionic Liquid Crystals

N-Alkyl-N-methylpyrrolidinium cations have been used for the design of ionic liquid crystals, including a new type of uranium-containing metallomesogen. Pyrrolidinium salts with bromide, bis(trifluoromethylsulfonyl)-imide, tetrafluoroborate, hexafluorophosphate, thiocyanate, tetrakis(2-thenoyltrifluoroacetonato)europate(III) and tetrabromouranyl] counteranions were prepared. For the bromide salts and tetrabromouranyl compounds, the chain length of the alkyl group CnH2n+1 was varied from eight to twenty carbon atoms (n =8. 10-20). The compounds show rich mesomorphic behaviour: highly ordered smectic phases (the crystal smectic E phase and the uncommon crystal smectic T phase), smectic A phases, and hexagonal. columnar phases were observed, depending on chain length and anion. This work gives better insight into the nature and formation of the crystal smectic T phase, and the Molecular requirements for the appearance of this highly ordered phase. This uncommon tetragonal mesophase is thoroughly discussed on the basis of detailed powder X-ray diffraction experiments and in relation to the existing literature. Structural models are proposed for self-assembly of the molecules within the smectic layers. In addition, the photophysical properties of the compounds containing a metal complex anion were investigated. For the uranium-containing mesogens, luminescence can be induced by dissolving them in an ionic: liquid matrix. The europium-containing compound shows intense red photoluminescence with high colour Purity.

Pyrrolidinium Ionic Liquid Crystals with Pendant Mesogenic Groups

New ionic liquid crystals (including ionic metallomesogens) based oil the pyrrolidinium core are presented. N-Methylpyrrolidine was quaternized with different mesogenic groups connected to a flexible, omega-bromosubstituted alkyl spacer. The length of the flexible alkyl spacer between the cationic head group and the rigid mesogenic group was varied. The substituted pyrrolidinium cations were combined with bromide, bis(trifluoromethylsulfonyl)imide, tetrakis (2-thenoyltrifluoroacetonato)europate(III), and tetrabromouranyl anions. The influence of the type of mesogenic unit, the lengths of the flexible spacer and terminal alkyl chain, the size of the mesogenic group, and the type of anion oil the thermotropic mesomorphic behavior was investigated. Furthermore, the phase behavior was thoroughly compared with the previously reported mesomorphism of N-alkyl-N-methylpyrrolidinium salts. Low-ordered smectic A phases of the de Vries type, smectic C phases, higher-ordered smectic F/I phases, as well its crystal smectic phases (E and G, J, H, or K) were observed and investigated by polarizing optical microscopy, differential scanning calorimetry, and powder X-ray diffraction.

Understanding the Effects of Ionicity in Salts, Solvates, Co-Crystals, Ionic Co-Crystals, and Ionic Liquids, Rather than Nomenclature, Is Critical to Understanding Their Behavior

The incorporation of active pharmaceutical ingredients (APIs) into multicomponent solid forms (such as salts and co-crystals) or liquid forms (such as ionic liquids (ILs) or deep eutectic mixtures) is important in optimizing the efficacy and delivery of APIs. However, there is a current debate regarding the classification of these multicomponent systems based on their ionicity which could interfere with their consideration in important applications. Multicomponent systems of intermediate ionicity can show a combination of properties, leading to behavior that is neither strictly typical of either purely ionic or purely neutral compounds, nor easily described as intermediate between the two. In this perspective, we attempt to illustrate the problems in classifying multicomponent APIs based on one of two categories by discussing selected literature regarding solid and liquid multicomponent APIs and presenting the crystal structures of some relevant systems as case studies. It is clear that a focus on restrictive nomenclature carries with it the risk that a thorough examination of the physicochemical properties of the compounds will be overlooked.

The phase behaviour of 1-alkyl-3-methylimidazolium tetrafluoroborates; ionic liquids and ionic liquid crystals

Air- and water-stable 1-alkyl-3-methylimidazolium tetrafluoroborate salts with the general formula [C-mim][BF] (n = 0-18) have been prepared by metathesis from the corresponding chloride or bromide salts. The salts have been characterised by H NMR and IR spectroscopy, microanalysis, polarising optical microscopy and differential scanning calorimetry. Those with short alkyl chains (n = 2-10) are isotropic ionic liquids at room temperature and exhibit a wide liquid range, whereas the longer chain analogues are low melting mesomorphic crystalline solids which display an enantiotropic smectic A mesophase. The thermal range of the mesophase increases with increasing chain length and in the case of the longest chain salt prepared, [C-mim][BF], the mesophase range is ca. 150°C.

Ab initio molecular dynamics simulation of a room temperature ionic liquid

Ab initio molecular dynamics simulations have been performed for the first time on the room-temperature organic ionic liquid dimethyl imidazolium chloride [DMIM][Cl] using density functional theory. The aim is to compare the local liquid structure with both that obtained from two different classical force fields and from neutron scattering experiments. The local structure around the cation shows significant differences compared to both the classical calculations and the neutron results. In particular, and unlike in the gas-phase ion pair, chloride ions tend to be located near a ring C-H proton in a position suggesting hydrogen bonding. The results are used to suggest ways in which the classical potentials may be improved.

Small angle neutron scattering from 1-alkyl-3-methylimidazolium hexafluorophosphate ionic liquids ([C(n)mim][PF6], n=4, 6, and 8)

The presence of local anisotropy in the bulk, isotropic, and ionic liquid phases-leading to local mesoscopic inhomogeneity-with nanoscale segregation and expanding nonpolar domains on increasing the length of the cation alkyl-substituents has been proposed on the basis of molecular dynamics (MD) simulations. However, there has been little conclusive experimental evidence for the existence of intermediate mesoscopic structure between the first/second shell correlations shown by neutron scattering on short chain length based materials and the mesophase structure of the long chain length ionic liquid crystals. Herein, small angle neutron scattering measurements have been performed on selectively H/D-isotopically substituted 1-alkyl-3-methylimidazolium hexafluorophosphate ionic liquids with butyl, hexyl, and octyl substituents. The data show the unambiguous existence of a diffraction peak in the low-Q region for all three liquids which moves to longer distances (lower Q), sharpens, and increases in intensity with increasing length of the alkyl substituent. It is notable, however, that this peak occurs at lower values of Q (longer length scale) than predicted in any of the previously published MD simulations of ionic liquids, and that the magnitude of the scattering from this peak is comparable with that from the remainder of the amorphous ionic liquid. This strongly suggests that the peak arises from the second coordination shells of the ions along the vector of alkyl-chain substituents as a consequence of increasing the anisotropy of the cation, and that there is little or no long-range correlated nanostructure in these ionic liquids.

Thermotropic Ruthenium(II)-Containing Metallomesogens Based on Substituted 1,10-Phenanthroline Ligands

Imidazo[4,5-f]-1,10-phenanthroline and pyrazino[2,3-f]-1,10-phenanthroline substituted with long alkyl chains are versatile ligands for the design of metallomesogens because of the ease of ligand substitution. Whereas the ligands and the corresponding rhenium(I) complexes were not liquid-crystalline, mesomorphism was observed for the corresponding ionic ruthenium(II) complexes with chloride, hexafluorophosphate, and bistriflimide counterions. The mesophases were identified as smectic A phases by high-temperature small-angle X-ray scattering (SAXS) using synchrotron radiation. The transition temperatures depend on the anion, the highest temperatures being observed for the chloride salts and the lowest for the bistriflimide salts. The ruthenium(II) complexes are examples of luminescent ionic liquid crystals.

The electrochemical oxidation and reduction of nitrate ions in the room temperature ionic liquid [C(2)mim][NTf2]; the latter behaves as a 'melt' rather than an 'organic solvent'

The electrochemical oxidation of 1-butyl-3-methylimidazolium nitrate [C(4)mim][NO3] was studied by cyclic voltammetry in the room temperature ionic liquid (RTIL) 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide [C(2)mim][NTf2]. A sharp peak was observed on a Pt microelectrode (d = 10 mu m), and a diffusion coefficient at infinite dilution of ca. 2.0 x 10(-11) m(2) s(-1) was obtained. Next, the cyclic voltammetry of sodium nitrate (NaNO3) and potassium nitrate (KNO3) was studied, by dissolving small amounts of solid into the RTIL [ C2mim][ NTf2]. Similar oxidation peaks were observed, revealing diffusion coefficients of ca. 8.8 and 9.0 x 10(-12) m(2) s(-1) and solubilities of 11.9 and 10.8 mM for NaNO3 and KNO3, respectively. The smaller diffusion coefficients for NaNO3 and KNO3 (compared to [C(4)mim][NO3]) may indicate that NO3- is ion-paired with Na+ or K+. This work may have applications in the electroanalytical determination of nitrate in RTIL solutions. Furthermore, a reduction feature was observed for both NaNO3 and KNO3, with additional anodic peaks indicating the formation of oxides, peroxides, superoxides and nitrites. This behaviour is surprisingly similar to that obtained from melts of NaNO3 and KNO3 at high temperatures ( ca. 350 - 500 degrees C), and this observation could significantly simplify experimental conditions required to investigate these compounds. We then used X-ray photoelectron spectroscopy (XPS) to suggest that disodium( I) oxide (Na2O), which has found use as a storage compound for hydrogen, was deposited on a Pt electrode surface following the reduction of NaNO3.

Extended electrochemical windows made accessible by room temperature ionic liquid/organic solvent electrolyte systems

The electrochemical windows of acetonitrile solutions doped with 0.1 m concentrations of several ionic liquids were examined by cyclic voltammetry at gold and platinum microelectrodes. These results were compared with those observed in the commonly used 0.1 m tetrabutylammonium perchlorate/acetonitrile system as well as with neat ionic liquids. The use of a trifluorotris(pentofluoroethyl)phosphate-based ionic liquid, specifically, as supporting electrolyte in acetonitrile solutions affords a wider anodic window, which is attributed to the high stability of the anionic component of these intrinsically conductive and thermally robust compounds.

Room-temperature ionic liquids as replacements for organic solvents in multiphase bioprocess operations

Organic solvents are widely used in a range of multiphase bioprocess operations including the liquid-liquid extraction of antibiotics and two-phase biotransformation reactions. There are, however, considerable problems associated with the safe handling of these solvents which relate to their toxic and flammable nature. In this work we have shown for the first time that room-temperature ionic liquids, such as 1-butyl-3-methylimidazolium hexafluorophosphate, [bmim][PF6], can be successfully used in place of conventional solvents for the liquid-liquid extraction of erythromycin-A and for the Rhodococcus R312 catalyzed biotransformation of 1,3-dicyanobenzene (1,3-DCB) in a liquid-liquid, two-phase system. Extraction of erythromycin with either butyl acetate or [bmim][PF6] showed that values of the equilibrium partition coefficient, K, up to 20-25 could be obtained for both extractants. The variation of K with the extraction pH was also similar in the pH range 5-9 though differed significantly at higher pH values. Biotransformation of 1,3-DCB in both water-toluene and water-[bmim][PF6] systems showed similar profiles for the conversion of 1,3-DCB initially to 3-cyanobenzamide and then 3-cyanobenzoic acid. The initial rate of 3-cyanobenzamide production in the water-[bmim][PF6] system was somewhat lower, however, due to the reduced rate of 1,3-DCB mass transfer from the more viscous [bmim] [PF,] phase. it was also shown that the specific activity of the biocatalyst in the water-[bmim][PF6] system was almost an order of magnitude greater than in the water-toluene system which suggests that the rate of 3-cyanobenzamide production was limited by substrate mass transfer rather than the activity of the biocatalyst. (C) 2000 John Wiley & Sons, Inc.

Crystal structures of imidazolium bis(trifluoromethanesulfonyl)imide 'ionic liquid' salts: the first organic salt with a cis-TFSI anion conformation

Crystal structures of two examples of an important class of ionic liquids, 1,3-dimethylimidazolium and 1,2,3-triethylimidazolium bis(trifluoromethanesulfonyl)imide have been characterized by single crystal X-ray diffraction. The anion in the 1,3-dimethylimidazolium example (mp 22 degreesC), adopts an unusual cis-geometry constrained by bifurcated cation-anion C-H...O hydrogen-bonds from the imidazolium cation to the anion resulting in the formation of fluorous layers within the solid-state structure. In contrast, in the 1,2,3-triethylimidazolium salt (mp 57 degreesC), the ions are discretely packed with only weak C-H...O contacts between the ions close to the van der Waals separation distances, and with the anion adopting the twisted conformation observed for all other examples from the limited set of organic bis( trifluoromethanesulfonyl) imide crystal structures. The structures are discussed in terms of the favorable physical properties that bis(trifluoromethanesulfonyl) imide anions impart in ionic liquids.

Lead(II) chloride ionic liquids and organic/inorganic hybrid materials - a study of chloroplumbate(II) speciation

A range of chloroplumbate(II) organic salts, based on the two cations, 1-ethyl-3-methylimidazolium and trihexyl(tetradecyl) phosphonium, was prepared by ionothermal synthesis. Depending on the structure of the organic cation and on the molar ratio of PbCl2 in the product,.PbCl2, the salts were room-temperature ionic liquids or crystalline organic/inorganic hybrid materials. The solids were studied using Raman spectroscopy; the crystal structure of [C(2)mim]{PbCl3} was determined and shown to contain 1D infinite chloroplumbate(II) strands formed by edge-sharing tetragonal pyramids of pentacoordinate (PbCl5) units. The liquids were analysed using Pb-207 NMR and Raman spectroscopies, as well as viscometry. Phase diagrams were constructed based on differential scanning calorimetry (DSC) measurements. Discrete anions: [PbCl4](2-) and [PbCl3](-), were detected in the liquid state. The trichloroplumbate(II) anion was shown to have a flexible structure due to the presence of a stereochemically-active lone pair. The relationship between the liquid phase anionic speciation and the structure of the corresponding crystalline products of ionothermal syntheses was discussed, and the data were compared with analogous tin(II) systems.

Alkylated organic cages: from porous crystals to neat liquids

Rigid organic iminospherand cages are rendered meltable by multiple alkylation; below their melting points they can take the form of permanently porous crystals, crystals unstable to desolvation or nonporous glassy solids depending on chain length and branching; melting points as low as 50 degrees C are observed and a fully Newtonian liquid phase is obtained above 80 degrees C. Thin glassy fibres can be drawn out from a molten phase.