Acid-base property of N-methylimidazolium-based protic ionic liquids depending on anion.

Proton-donating and ionization properties of several protic ionic liquids (PILs) made from N-methylimidazole (Mim) and a series of acids (HA) have been assessed by means of potentiometric and calorimetric titrations. With regard to strong acids, bis(trifluoromethanesulfonyl) amide (Tf(2)NH) and trifluoromethanesulfonic acid (TfOH), it was elucidated that the two equimolar mixtures with Mim almost consist of ionic species, HMim(+) and A(-), and the proton transfer equilibrium corresponding to autoprotolysis in ordinary molecular liquids was established. The respective autoprotolysis constants were successfully evaluated, which indicate the proton-donating abilities of TfOH and Tf(2)NH in the respective PILs are similar.

Surface analysis of ionic liquids with and without lithium salt using X-ray photoelectron spectroscopy.

X-ray photoelectron spectroscopy (XPS) was applied to a neat ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [EMI(+)][Tf(2)N(-)] and its lithium salt solution at room temperature to clarify the composition and structure of its near-surface region. Core level peaks were recorded for Li 1s, N 1s, C 1s, F 1s, O 1s, S 2s, and S 2p. Valence band XPS spectra (0-40 eV binding energy) were also studied.

Physicochemical and acid-base properties of a series of 2-hydroxyethylammonium-based protic ionic liquids.

Physicochemical properties such as a thermal behavior, ionic conductivity, viscosity and density, and acid-base properties of a new class of 2-hydroxyethylammonium-based protic ionic liquids (PILs) have been investigated. Thirty-six potential PILs were surveyed to find 32 salts with a melting point below 373 K. Among them, [(EtOH)(n)Et((3-n))NH(+)][TFS(-)] (Et, C(2)H(5); n = 0 - 3) and [(EtOH)(2)EtNH(+)][X(-)] (X = TFS, trifluoromethanesulfonate; TFSA, bis(trifluoromethanesulfonyl)amide; NO(3)) were studied in terms of the Walden plots, molar volume and auto-protolysis reaction for effect of the number of 2-hydroxyethyl groups introduced in the cations and for dependence of the anion nature, respectively.

Free-energy and structural analysis of ion solvation and contact ion-pair formation of Li(+) with BF4(-) and PF6(-) in water and carbonate solvents.

Free energy of contact ion-pair (CIP) formation of lithium ion with BF(4)(-) and PF(6)(-) in water, propylene carbonate (PC), dimethyl carbonate (DMC) are quantitatively analyzed using MD simulations combined with the energy representation method. The relative stabilities of the mono-, bi-, and tridentate coordination structures are assessed with and without solvent, and water, PC, and DMC are found to favor the CIP-solvent contact. The monodentate structure is typically most stable in these solvents, whereas the configuration is multidentate in vacuum.

Structural heterogeneity and unique distorted hydrogen bonding in primary ammonium nitrate ionic liquids studied by high-energy X-ray diffraction experiments and MD simulations.

Liquid structure and the closest ion-ion interactions in a series of primary alkylammonium nitrate ionic liquids [C(n)Am(+)][NO(3)(-)] (n = 2, 3, and 4) were studied by means of high-energy X-ray diffraction (HEXRD) experiments with the aid of molecular dynamics (MD) simulations. Experimental density and X-ray structure factors are in good accordance with those evaluated with MD simulations. With regard to liquid structure, characteristic peaks appeared in the low Q (Q: a scattering vector) region of X-ray structure factors S(Q)'s for all ionic liquids studied here, and they increased in intensity with a peak position shift toward the lower Q side by increasing the alkyl chain length.

Experimental evidences for molecular origin of low-Q peak in neutron/x-ray scattering of 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ionic liquids.

Short- and long-range liquid structures of [C(n)mIm(+)][TFSA(-)] with n = 2, 4, 6, 8, 10, and 12 have been studied by high-energy x-ray diffraction (HEXRD) and small-angle neutron scattering (SANS) experiments with the aid of MD simulations. Observed x-ray structure factor, S(Q), for the ionic liquids with the alkyl-chain length n > 6 exhibited a characteristic peak in the low-Q range of 0.2-0.

Dependence of the conformational isomerism in 1-n-butyl-3-methylimidazolium ionic liquids on the nature of the halide anion.

The conformational isomerism of the 1-n-butyl-3-methylimidazolium cation, [C(4)mim](+), in halide-based ionic liquids--[C(4)mim]Cl, [C(4)mim]Br, and [C(4)mim]I--was explored by Raman spectroscopy. The [C(4)mim](+) cation exhibits trans-gauche conformational isomerism with respect to the N1-C7-C8-C9 dihedral angle of its butyl chain. The thermodynamics of trans-gauche conversion were analyzed through the successful evaluation of the corresponding Gibbs free energy, Δ(iso)G°, enthalpy, Δ(iso)H°, and entropy, Δ(iso)S°, of conformational isomerization.

Raman spectroscopic studies and ab initio calculations on conformational isomerism of 1-butyl-3-methylimidazolium bis-(trifluoromethanesulfonyl)amide solvated to a lithium ion in ionic liquids: effects of the second solvation sphere of the lithium ion.

Raman spectra of the ionic liquid, 1-butyl-3-methylimidazolium bis-(trifluoromethanesulfonyl)amide [C(4)mIm][TFSA] containing a LiTFSA salt were measured for the lithium salt mole fractions x(Li) = 0.000, 0.053, 0.

Solvation and microscopic properties of ionic liquid/acetonitrile mixtures probed by high-pressure infrared spectroscopy.

The microscopic features of binary mixtures formed by an ionic liquid (EMI(+)TFSA(-) or EMI(+)FSA(-)) and a molecular liquid (acetonitrile or methanol) have been investigated by high-pressure infrared spectroscopy. On the basis of its responses to changes in pressure and concentration, the imidazolium C-H appears to exist at least in two different forms, i.e.

Relationships between center atom species (N, P) and ionic conductivity, viscosity, density, self-diffusion coefficient of quaternary cation room-temperature ionic liquids.

The physicochemical properties (ionic conductivity, viscosity, density, and self-diffusion coefficient) of tri-n-ethylpentylphosphonium bis(trifluoromethanesulfonyl)amide (TEPP-TFSA) ionic liquid were compared with those of tri-n-ethylpentylammonium bis(trifluoromethanesulfonyl)amide (TEPA-TFSA). Compared with the TEPA-TFSA ionic liquid, the density and viscosity of the phosphorus ionic liquid are lower, although the ionic conductivity and self-diffusion coefficient are higher. The molar conductivities were compared for the values obtained by the electrochemical impedance method (electrochemical conductivity) and the calculated from the pulsed-gradient spin-echo nuclear magnetic resonance method (diffusive conductivity).

Structural change of ionic association in ionic liquid/water mixtures: a high-pressure infrared spectroscopic study.

High-pressure infrared measurements were carried out to observe the microscopic structures of two imidazolium-based ionic liquids, i.e., 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide [EMI(+)(CF(3)SO(2))(2)N(-), EMI(+)TFSA(-)] and 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)amide [EMI(+)(FSO(2))(2)N(-), EMI(+)FSA(-)].

Raman spectroscopic study, DFT calculations and MD simulations on the conformational isomerism of N-alkyl-N-methylpyrrolidinium bis-(trifluoromethanesulfonyl) amide ionic liquids.

The conformational behaviors of N-alkyl-N-methylpyrrolidinium bis-(trifluoromethanesulfonyl) amide ionic liquids (alkyl; propyl and butyl, [P(1n)][TFSA]; n = 3 and 4) were studied by Raman spectroscopy in the frequency range of 200-1700 cm(-1) at different temperatures. Observed Raman spectra in the frequency range 870-960 cm(-1) for [P(13)][TFSA] and at 860-950 cm(-1) for [P(14)][TFSA] depend on the temperature, indicating that pseudo rotational isomerization of the pyrrolidinium ring exists in the ionic liquids. DFT calculations revealed that the pseudo rotational potential energy surfaces for P(13)(+) and P(14)(+) ions were similar to each other, i.

Phase transition and conductive acceleration of phosphonium-cation-based room-temperature ionic liquid.

An unusual ionic conduction phenomenon related to the phase transition of a novel phosphonium-cation-based room-temperature ionic liquid (RTIL) is reported; we found that in the phase change upon cooling, a clear increase in ionic conductivity was seen as the temperature was lowered, which differs from widely known conventional RTILs; clearly, our finding of abnormality of the correlation between temperature change and ionic conduction is the first observation in the electrolyte field.

Solvation structures of some transition metal(II) ions in a room-temperature ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide.

Solvation structures of manganese(II), cobalt(II), nickel(II) and zinc(II) ions in 1-ethyl-3-methylimidazolium bis(trifluoro-methanesulfonyl) amide (EMI(+)TFSA(-)) have been studied by UV-Vis, FT-IR and FT-Raman spectra. The ionic liquid involves TFSA(-) conformers with C(1) (cis) and C(2) (trans) symmetries, and both conformers coexist in equilibrium in the liquid state. The results showed that these metal(II) ions are all six-coordinated with three TFSA(-) ions, i.

Acidity and basicity of aqueous mixtures of a protic ionic liquid, ethylammonium nitrate.

Ethylammonium nitrate (EAN) is composed of C(2)H(5)NH(3)(+) and NO(3)(-) ions, which behave as an acid and a base, respectively. The ionic liquid thus involves small amounts of C(2)H(5)NH(2) and HNO(3) molecules owing to proton transfer from C(2)H(5)NH(3)(+) to NO(3)(-). The equilibrium constant K(s) (= [C(2)H(5)NH(2)][HNO(3)]), which corresponds to the autoprotolysis constant of water, was obtained to be ca.

Raman spectroscopic study on alkaline metal ion solvation in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ionic liquid.

The Raman spectra for 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide [BMI][TFSA] containing alkaline metal salts of TFSA(-), MTFSA (M = Li, Na, K and Cs), were recorded in the frequency range of 200-1800 cm(-1), with varying salt concentrations at 298 K. With Li(+) and Na(+) ions, at the frequency range of 730-760 cm(-1), new Raman bands ascribable to the anion bound to the ions appeared at higher frequency relative to that found in the neat ionic liquid. On the other hand, with K(+) and Cs(+) ions, single Raman bands were solely observed.

Solvation of lithium ion in N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)-amide using Raman and multinuclear NMR spectroscopy.

The solvation structure of the Li(I) species in N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethane-sulfonyl) amide (DEMETFSA) was studied by measuring the Raman and multinuclear NMR spectra of DEMETFSA solutions containing LiTFSA of various concentrations (0.12-1.92 mol kg(-1), [TFSA(-)]/[Li(I)] = 20.

Potential energy landscape of bis(fluorosulfonyl)amide.

The conformational landscape of the bis(fluorosulfonyl)amide, [FSI]-, anion was analyzed using data obtained from Raman spectroscopy, molecular dynamics (MD), and ab initio studies. The plotting of three-dimensional potential energy surfaces and the corresponding MD simulation conformer-population histograms show the existence of two stable isomers, C2 (trans) and C1 (cis) conformers, and confirm the nature of the anion as a flexible molecule capable of interconversion between conformers in the liquid state. In ionic liquids, the two [FSI]- conformers coexist in equilibrium, a result confirmed by the Raman data.

Liquid structure of room-temperature ionic liquid, 1-Ethyl-3-methylimidazolium bis-(trifluoromethanesulfonyl) imide.

The liquid structure of 1-ethyl-3-methylimidazolium bis-(trifluoromethanesulfonyl) imide (EMI(+)TFSI(-)) has been studied by means of large-angle X-ray scattering (LAXS), (1)H, (13)C, and (19)F NMR, and molecular dynamics (MD) simulations. LAXS measurements show that the ionic liquid is highly structured with intermolecular interactions at around 6, 9, and 15 A. The intermolecular interactions at around 6, 9, and 15 A are ascribed, on the basis of the MD simulation, to the nearest neighbor EMI(+).

A tale of two ions: the conformational landscapes of bis(trifluoromethanesulfonyl)amide and N,N-dialkylpyrrolidinium.

The conformational landscapes of two commonly used ionic liquid ions, the anion bis(trifluoromethanesulfonyl)amide (Ntf2) and the cations N-propyl- and N-butyl-N-methylpyrrolidinium, were investigated using data obtained from Raman spectroscopy, molecular dynamics, and ab initio techniques. In the case of Ntf2, the plotting of three-dimensional potential energy surfaces (PES) and the corresponding molecular dynamics (MD) simulations confirmed the existence of two stable isomers (each existing as a pair of enantiomers) and evidenced the nature of the anion as a flexible, albeit hindered, molecule capable of interconversion between conformers in the liquid state, a result confirmed by the Raman data. In the case of the N,N-dialkylpyrrolidinium cations, the PES show a much more limited conformational behavior of the pyrrolidinium ring (pseudorotation).

Lithium ion solvation in room-temperature ionic liquids involving bis(trifluoromethanesulfonyl) imide anion studied by Raman spectroscopy and DFT calculations.

The solvation structure of the lithium ion in room-temperature ionic liquids 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide (EMI(+)TFSI(-)) and N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide (BMP(+0TFSI(-)) has been studied by Raman spectroscopy and DFT calculations. Raman spectra of EMI(+)TFSI(-) and BMP(+)TFSI(-) containing Li(+)TFSI(-) over the range 0.144-0.

Anion conformation of low-viscosity room-temperature ionic liquid 1-ethyl-3-methylimidazolium bis(fluorosulfonyl) imide.

Anion conformation of a low-viscosity room-temperature ionic liquid 1-ethyl-3-methylimidazolium bis(fluorosulfonyl) imide (EMI+FSI-) has been studied by Raman spectra and theoretical DFT calculations. Three strong Raman bands were found at 293, 328, and 360 cm(-1), which are ascribed to the FSI- ion. These Raman bands show significant temperature dependence, implying that two FSI- conformers coexist in equilibrium.

Solvation number and conformation of N,N-dimethylacrylamide and N,N-dimethylpropionamide in the coordination sphere of the cobalt(II) ion in solution studied by FT-IR and FT-Raman spectroscopy.

The solvation number and conformation of N,N-dimethylacrylamide (DMAA) in the coordination sphere of the cobalt(II) ion in solution were studied, and compared with those of N,N-dimethylpropionamide (DMPA) by means of FT-Raman and FT-IR spectroscopy. Both solvents are present as either the planar cis or nonplanar staggered conformer in equilibrium, and the former is more stable in the bulk. As these solvents solvate the metal ion through the carbonyl O atom of the acryl (DMAA) or propionyl (DMPA) group, the solvation structure around the metal ion is highly congested to reduce the solvation number and/or to lead to a conformational geometry change of solvent.

Solvation structure of Li+ in concentrated LiPF6-propylene carbonate solutions.

Time-of-flight neutron diffraction measurements were carried out for 6Li/7Li isotopically substituted 10 mol % LiPF6-propylene carbonate-d6 (PC-d6) solutions, in order to obtain structural information on the first solvation shell of Li+. Structural parameters concerning the nearest neighbor Li+..