Designing Ionic Liquids: 1-Butyl-3-Methylimidazolium Cations with Substituted Tetraphenylborate Counterions

Anion influences on reactivity and NMR spectroscopic features of NHC precursors

A series of 16 benzimidazolium salts of the type ⁱPr₂-bimyH⁺X⁻ with various anions X were synthesized and characterized by various spectroscopic and spectrometric methods. Significant anion and solvent effects on the chemical shifts of the C2–H protons were found, which allows for a ranking of the anions in terms of their hydrogen-bond acceptor properties. Stronger acceptors could increase the acidity of their respective salts leading to a faster H/D exchange. Similar but less pronounced anion influences were detected for the ¹³C_C2 NMR resonances, while ¹J_C2–H coupling constants appear to be anion and solvent independent.

The influences of 16 different counteranions on hydrogen-bondings, C–H acidities and ¹J_C2–H coupling constants of azolium salts have been studied.

Imidazolium-based ionic liquids with large weakly coordinating anions

An investigation into the intramolecular interactions in a series of imidazolium salts with weakly coordinating anions reveals that it is possible to control the strength and location of hydrogen bonding by varying the substituents on the imidazolium cation.

Novel diol functionalized dicationic ionic liquids: synthesis, characterization and DFT calculations on H-bonding influence on thermophysical properties

DFT was used to investigate the roles of H-bonding on the thermophysical properties of two novel diol functionalized dicationic ionic liquids.

Ionic liquids as a potential tool for drug delivery systems

The pharmaceutical industries face a series of challenges in the delivery of many newly developed drug molecules because of their low solubility, bioavailability, stability and polymorphic conversion.

Physico-chemical properties and phase behavior of the ionic liquid-β-cyclodextrin complexes

The solubility of β-cyclodextrin (β-CD) in ionic liquids (ILs) and the activity coefficients at infinite dilution (γ13(∞)) of more than 20 solutes (alkanes, aromatic hydrocarbons, alcohols) were measured in four chosen ionic liquids, their mixtures with β-CD, and in the β-CD at high temperatures from 338 to 398 K using the inverse gas chromatography. The intermolecular interactions, inclusion complexes and the possible increasing of the solubility of β-CD in water using the IL are presented. The solubility of β-CD in ten chosen hydrophobic ILs at the temperature T = 423 K was detected. The solid-liquid phase diagrams (SLE) of {IL (1) + β-CD (2)} binary systems at the high mole fraction of the IL were measured for three systems (1-ethyl-3-methylimidazolium chloride, [EMIM][Cl], 1-ethyl-3-methylimidazolium bromide, [EMIM][Br]; and for 1-butyl-3-methylimidazolium chloride, [BMIM][Cl]). The eutectic points were determined at the high IL concentration for all binary systems. The intermolecular interaction and the possibility of inclusion complexes of the IL and/or solvents with β-CD were discussed. The infrared spectroscopy, IR was used for the description of the intermolecular interactions in the (β-CD + IL) systems. It was shown via the activity coefficients at infinite dilution results that the inclusion complexes are dependent on the temperature. The addition of β-CD to the IL does not improve the selectivity of the separation of the aliphatics from aromatics.

Synthesis and reactions of N-heterocyclic carbene boranes

Boranes are widely used Lewis acids and N-heterocyclic carbenes (NHCs) are popular Lewis bases, so it is remarkable how little was known about their derived complexes until recently. NHC-boranes are typically readily accessible and many are so stable that they can be treated like organic compounds rather than complexes. They do not exhibit "borane chemistry", but instead are proving to have a rich chemistry of their own as reactants, as reagents, as initiators, and as catalysts. They have significant potential for use in organic synthesis and in polymer chemistry. They can be used to easily make unusual complexes with a broad spectrum of functional groups not usually seen in organoboron chemistry. Many of their reactions occur through new classes of reactive intermediates including borenium cations, boryl radicals, and even boryl anions. This Review provides comprehensive coverage of the synthesis, characterization, and reactions of NHC-boranes.

Near-infrared fluorescent nanoGUMBOS for biomedical imaging

Herein, we report on near-infrared (NIR) fluorescent nanoparticles generated from an emergent class of materials we refer to as a Group of Uniform Materials Based on Organic Salts (GUMBOS). GUMBOS are largely frozen ionic liquids, although the concept is more general and is also easily applied to solid ionic materials with melting points in excess of 100 degrees C. Nanoparticles based on GUMBOS (nanoGUMBOS) derived from a NIR fluorophore are prepared using a reprecipitation method and evaluated for in vivo fluorescence imaging. Due to their uniformity, single-step preparation, and composite nature, nanoGUMBOS help to resolve issues with dye leakage problems innate to alternate cellular stains and unlock a myriad of applications for these materials, highlighting exciting possibilities for multifunctional nanoGUMBOS.

Influence of gamma irradiation on hydrophobic room-temperature ionic liquids [BuMeIm]PF6 and [BuMeIm](CF3SO2)2N

Stability of neat hydrophobic Room-Temperature Ionic Liquids (RTIL) [BuMeIm]X, where [BuMeIm]+ is 1-butyl-3-methylimidazolium and X- is PF6-, and (CF3SO2)2N-, was studied under gamma radiolysis (137Cs) in an argon atmosphere and in air. It was found that the density, surface tension, and refraction index of RTILs are unchanged even by an absorbed dose of approximately 600 kGy. Studied RTILs exhibit considerable darkening when subjected to gamma irradiation. The light absorbance of ionic liquids increases linearly with the irradiation dose. Water has no influence on radiolytic darkening. A comparative study of [BuMeIm]X and [Bu4N][Tf2N] leads to the conclusion that the formation of colored products is related to gamma radiolysis of the [BuMeIm]+ cation. The radiolytic darkening kinetics of RTILs is influenced by the anions as follows: Cl- < (CF3SO2)2N- < PF6-. Electrospray ionization mass spectrometry and NMR analysis reveal the presence of nonvolatile radiolysis products at concentrations below 1 mol% for an absorbed dose exceeding 1200 kGy. Initial step of BuMeIm+ cation radiolysis is the loss of the Bu* group, the H* atom from the 2 position on the imidazolium ring, and the H* atom from the butyl chain. Radiolysis of ionic liquid anions yields F* and CF3* from PF6- and [Tf2N]-, respectively. Recombinations of these primary products of radiolysis lead to various polymeric and acidic species.

Ionic Liquids: The Neglected Issues

There has been an explosion of interest in ionic liquids in the last five years that has resulted in the discovery of a vast number of new ionic liquids with a wide range of interesting applications. Although ionic liquids are invariably described as highly stable green solvents, thorough investigations quantifying their purity, stability, biodegradability, and toxicity have lagged behind the pace of other research in the area. This review addresses these key issues and summarizes the approaches that have been developed for recycling ionic liquids.

Chromatographic and spectroscopic methods for the determination of solvent properties of room temperature ionic liquids

Room temperature ionic liquids are novel solvents with favorable environmental and technical features. Synthetic routes to over 200 room temperature ionic liquids are known but for most ionic liquids physicochemical data are generally lacking or incomplete. Chromatographic and spectroscopic methods afford suitable tools for the study of solvation properties under conditions that approximate infinite dilution. Gas-liquid chromatography is suitable for the determination of gas-liquid partition coefficients and activity coefficients as well as thermodynamic constants derived from either of these parameters and their variation with temperature. The solvation parameter model can be used to define the contribution from individual intermolecular interactions to the gas-liquid partition coefficient. Application of chemometric procedures to a large database of system constants for ionic liquids indicates their unique solvent properties: low cohesion for ionic liquids with weakly associated ions compared with non-ionic liquids of similar polarity; greater hydrogen-bond basicity than typical polar non-ionic solvents; and a range of dipolarity/polarizability that encompasses the same range as occupied by the most polar non-ionic liquids. These properties can be crudely related to ion structures but further work is required to develop a comprehensive approach for the design of ionic liquids for specific applications. Data for liquid-liquid partition coefficients is scarce by comparison with gas-liquid partition coefficients. Preliminary studies indicate the possibility of using the solvation parameter model for interpretation of liquid-liquid partition coefficients determined by shake-flask procedures as well as the feasibility of using liquid-liquid chromatography for the convenient and rapid determination of liquid-liquid partition coefficients. Spectroscopic measurements of solvatochromic and fluorescent probe molecules in room temperature ionic liquids provide insights into solvent intermolecular interactions although interpretation of the different and generally uncorrelated "polarity" scales is sometimes ambiguous. All evidence points to the ionic liquids as a unique class of polar solvents suitable for technical development. In terms of designer solvents, however, further work is needed to fill the gaps in our knowledge of the relationship between ion structures and physicochemical properties.