Richard A. Bartsch

Influence of Structural Variations in 1‐Alkyl(aralkyl)‐3‐Methylimidazolium Hexafluorophosphates and Bis(trifluoromethylsulfonyl)imides on Physical Properties of the Ionic Liquids

A series of twenty four 1-alkyl(aralkyl)-3-methylimidazolium hexafluorophosphates and bis(trifluoromethyl-sulfonyl)imides are prepared and the influence of structural variations in the imidazolium cation and the identity of the anion on physical properties (phase transition, density, viscosity, and surface tension) of the ionic liquids is determined.

Effect of Cation Symmetry and Alkyl Chain Length on the Structure and Intermolecular Dynamics of 1,3-Dialkylimidazolium Bis(trifluoromethanesulfonyl)amide Ionic Liquids

In this article, the structure and intermolecular dynamics of 1,3-alkylmethylimidazolium bis(trifluoromethanesulfonyl)amides [C(n)mim][NTf(2)] with n = 2-5 are compared to those of 1,3-dialkylimidazolium bis(trifluoromethanesulfonyl)amides [(C(n))(2)im][NTf(2)] with n = 2-5. The structures of these room-temperature ionic liquids (RTILs) were studied by small-wide-angle X-ray scattering (SWAXS), and their intermolecular dynamics were studied by optical Kerr effect (OKE) spectroscopy. The SWAXS measurements indicate that, on a microscopic scale, the liquid structure of RTILs with symmetric cations is similar to that of RTILs with asymmetric cations. The OKE measurements indicate that the intermolecular dynamics of RTILs with symmetric cations are higher in frequency than those of RTILs with asymmetric cations. These results suggest that the local structure of RTILs with symmetric cations is more solid-like than that of RTILs with asymmetric cations. Further evidence for this difference in local structure on a mesoscopic spatial scale is that the width of the low-Q peak in the SWAXS data is narrower for [(C(5))(2)im][NTf(2)] than for [C(5)mim][NTf(2)]. Moreover, the structure and intermolecular dynamics of the RTILs with ethyl-substituted cations appear to be quite different from those of other RTILs within a given series. This difference is evidenced by a clear change in the dependence of the spectral parameters of the intermolecular part of the OKE spectrum on the alkyl chain length in going from n = 2 to n = 3. The dependence of the SWAXS and OKE data on alkyl chain length is discussed within the context of the nanoscale heterogeneities of RTILs.

Expanding the polarity range of ionic liquids

Abstract The polarity of several [X-mim]NTf 2 ionic liquids, as measured with solvatochromic dyes, Reichardts dye and Nile Red, may be varied over a wide range by attachment of functional group-containing substituents (X) to the imidazolium cation.

Effect of Cation Symmetry on the Morphology and Physicochemical Properties of Imidazolium Ionic Liquids

In this paper, the morphology and bulk physical properties of 1,3-dialkylimidazolium bis{(trifluoromethane)sulfonyl}amide ([(C(N/2))(2)im][NTf(2)]) are compared to that of 1-alkyl-3-methylimidazolium bis{(trifluoromethane)sulfonyl}amide ([C(N-1)C(1)im][NTf(2)]) for N = 4, 6, 8, and 10. For a given pair of ionic liquids (ILs) with the same N, the ILs differ only in the symmetry of the alkyl substitution on the imidazolium ring of the cation. Small-wide-angle X-ray scattering measurements indicate that, for a given symmetric/asymmetric IL pair, the structural heterogeneities are larger in the asymmetric IL than in the symmetric IL. The correlation length of structural heterogeneities for the symmetric and asymmetric salts, however, is described by the same linear equation when plotted versus the single alkyl chain length. Symmetric ILs with N = 4 and 6 easily crystallize, whereas longer alkyl chains and asymmetry hinder crystallization. Interestingly, the glass transition temperature is found to vary inversely with the correlation length of structural heterogeneities and with the length of the longest alkyl chain. Whereas the densities for a symmetric/asymmetric IL pair with a given N are nearly the same, the viscosity of the asymmetric IL is greater than that of the symmetric IL. Also, an even-odd effect previously observed in molecular dynamics simulations is confirmed by viscosity measurements. We discuss in this paper how the structural heterogeneities and physical properties of these ILs are consistent with alkyl tail segregation.

A Calixarene-Based Fluorogenic Reagent for Selective Mercury(II) Recognition.

The first calixarene-based fluorogenic Hg(II)-selective extractant, 5,11,17,23-tetrakis(1,1-dimethylethyl)-25,27-bis(N-(5-dimethylaminonaphthalene-1-sulfonyl)carbamoylmethoxy)-26,28-dimethoxycalix[4]arene (2), is reported. In solvent extraction from aqueous acidic solutions (HNO(3)), 2 exhibits excellent selectivity for Hg(II) over a wide range of transition, alkali, and alkaline earth metal cations. Quenching of its fluorescence due to Hg(II) coordination is unaffected by the presence of 100-fold excesses of alkali metal cations, alkaline earth metal cations, Ag(I), Tl(I), Cd(II), Co(II), Cu(II), Ni(II), Pb(II), Pd(II), Zn(II), or Fe(III).

Chromofluorescent Indicator for Intracellular Zn2+/Hg2+ Dynamic Exchange

The fluorescence of NABQ increases remarkably in the presence of Zn(2+) and is quenched by Hg(2+). As shown by confocal imaging, NABQ-Zn(2+) can penetrate cells, where the bound Zn(2+) is exchanged for Hg(2+). This results in the concomitant export of Hg(2+) from the cells, showing that NABQ can act as a Zn(2+) carrier and as a Hg(2+) extracting agent in living cells.

Nanostructural Organization in Acetonitrile/Ionic Liquid Mixtures: Molecular Dynamics Simulations and Optical Kerr Effect Spectroscopy

The nanostructural organization and subpicosecond intermolecular dynamics in mixtures of acetonitrile and the ionic liquid (IL) 1-pentyl-3-methylimidazolium bis{(trifluoromethane)sulfonyl}amide ([C(5)mim][NTf(2)]) are studied as a function of concentration using molecular dynamics (MD) simulations and optical heterodyne-detected Raman-induced Kerr effect spectroscopy. The MD simulations show the IL to be nanostructurally organized into an ionic network and nonpolar domains, with CH(3)CN molecules localized in the interfacial region between the ionic network and nonpolar domains, as found previously by other researchers. The MD simulations indicate strong interactions between CH(3)CN and the hydrogen atoms on the imidazolium ring of the cation. The low-frequency (0-200 cm(-1)) intermolecular part of the reduced spectral densities (RSDs) of the mixtures narrows and shifts to lower frequency as the concentration of CH(3)CN increases. These spectral changes can be partly attributed to the increasing contribution of the low-frequency intermolecular modes of CH(3)CN to the RSD. At a given composition, the RSD of a mixture is found to be broader and higher in frequency than the corresponding ideal RSD given by the volume-fraction-weighted sum of the RSDs of the neat liquids. This difference is rationalized in terms of the competition between CH(3)CN-cation interactions and solute-induced disruption of the ionic networks.

Intermolecular Vibrational Motions of Solute Molecules Confined in Nonpolar Domains of Ionic Liquids

In this study, we address the following question about the dynamics of solute molecules in ionic liquids (ILs). Are the intermolecular vibrational motions of nonpolar molecules confined in the nonpolar domains formed by tail aggregation in ILs the same as those in an alkane solvent? To address this question, the optical Kerr effect (OKE) spectrum of CS(2) in the IL 1-pentyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([C(5)mim][NTf(2)]) was studied as a function of concentration at 295 K by the use of optical heterodyne-detected Raman-induced Kerr effect spectroscopy. The OKE spectrum broadens and shifts to higher frequency as the CS(2) concentration is decreased from 20 to 10 mol %; at lower concentrations, no further change in the width of the OKE spectrum is observed. Multicomponent line shape analysis of the OKE spectrum of 5 mol % CS(2) in [C(5)mim][NTf(2)] reveals that the CS(2) and [C(5)mim][NTf(2)] contributions to the spectrum are separable and that the CS(2) contribution is similar to the OKE spectrum of 5 mol % CS(2) in n-pentane with the spectrum being lower in frequency and narrower than that of neat CS(2). These results suggest that, at this concentration, CS(2) molecules are isolated from each other and mainly localized in the nonpolar domains of the IL.

Transport of alkali metal cations across liquid membranes by crown ether carboxylic acids

Abstract Competitive alkali metal transport from an alkaline aqueous source phase through a chloroform phase to an acidic aqueous receiving phase facilitated by nine crown ethers with pendant carboxylic acid groups has been investigated. Transport selectivity is controlled by the size of the polyether cavity of the carrier. Increasing the lipophilicity of the carrier, while maintaining a constant polyether cavity size, enhances the total transport rate but does not affect the selectivity. There is poor agreement between the results of competitive transport and the behavior anticipated on the basis of single cation transport studies.

Nanostructural organization in carbon disulfide/ionic liquid mixtures: Molecular dynamics simulations and optical Kerr effect spectroscopy

In this paper, the nanostructural organization and subpicosecond intermolecular dynamics in the mixtures of CS(2) and the room temperature ionic liquid (IL) 1-pentyl-3-methylimidazolium bis{(trifluoromethane)sulfonyl}amide ([C(5)mim][NTf(2)]) were studied as a function of concentration using molecular dynamics (MD) simulations and optical heterodyne-detected Raman-induced Kerr effect spectroscopy. At low CS(2) concentrations (<10 mol.% CS(2)/IL), the MD simulations indicate that the CS(2) molecules are localized in the nonpolar domains. In contrast, at higher concentrations (≥10 mol.% CS(2)/IL), the MD simulations show aggregation of the CS(2) molecules. The optical Kerr effect (OKE) spectra of the mixtures are interpreted in terms of an additivity model with the components arising from the subpicosecond dynamics of CS(2) and the IL. Comparison of the CS(2)-component with the OKE spectra of CS(2) in alkane solvents is consistent with CS(2) mainly being localized in the nonpolar domains, even at high CS(2) concentrations, and the local CS(2) concentration being higher than the bulk CS(2) concentration.