Tatsuya Umecky

Ionization Condition of Lithium Ionic Liquid Electrolytes under the Solvation Effect of Liquid and Solid Solvents

Ionization condition and ionic structures of the lithium ionic liquid electrolytes, LiTFSI/EMI-TFSI/(PEG or silica), were investigated through the measurements of ionic conductivity and diffusion coefficient. The size of the hydrodynamic lithium species (rLi) evaluated from the Stokes-Einstein equation was 0.90 nm before gelation with the PEG or silica. This reveals that the TFSI- anions from the solvent are coordinated on Li+ for solvation, forming, for example, Li(TFSI)4(3-) and Li(TFSI)2- in the electrolyte solution. By the dispersion of PEG for gelation, rLi increased up to 1.8 nm with the 10 wt % of PEG. This indicates that the lithium species is directly interacted with the oxygen sites on the polymer chains and the lithium species migrate, reflecting the polymer by hopping from site to site. In case of the silica dispersion, rLi decreased to 0.7 nm at 10 wt % silica. Although the silica surface with silanol groups fundamentally attracts Li+, the lithium does not migrate from site to site on the silica surface as in the gel of the polymer and follows random walk behavior in the network of the liquid-phase pathways in the two-phase gel. In the process, that solvated TFSI- anions are partially removed may be due to the attractive effect of H+, which was dissociated from the silanol group. It is concluded that the dispersed silica is effective to modify the hydrodynamic lithium species to be appropriate for charge transport as reducing the size and anionic charge of Li(TFSI)4(3-) by removing one or two TFSI- anions.

Direct measurements of ionic mobility of ionic liquids using the electric field applying pulsed gradient spin-echo NMR.

Ionic mobilities of the ionic liquids, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)amide,1-ethyl-3-methylimidazolium fluorosulfonyl-(trifluoromethylsulfonyl)amide, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) -amide, were measured using the electric field applying pulsed gradient spin-echo NMR technique. Observed mobilities were more than 1 order of magnitude greater than the values estimated from the diffusion coefficients measured under the equilibrium state without the electric field. Electric field dependence of the ionic mobility showed that the high mobility appeared above the threshold of the field strength with keeping the constant values. This indicates that the ions are orientated by the application of the electric field may be due to the dielectric polarization.

Alkoxy chains in ionic liquid anions; effect of introducing ether oxygen into perfluoroalkylborate on physical and thermal properties.

The melting point and viscosity of [CF(3)OCF(2)CF(2)BF(3)](-) based ionic liquids are significantly lower than those of [CF(3)CF(2)CF(2)CF(2)BF(3)](-) based ionic liquids, indicating that the oxygen atom plays a key role in the preparation of low-melting and low-viscosity ionic liquids.

Interactions of Perfluoroalkyltrifluoroborate Anions with Li Ion and Imidazolium Cation: Effects of Perfluoroalkyl Chain on Motion of Ions in Ionic Liquids

The stabilization energies (E(form)) for the formation of the perfluoroalkyltrifluoroborate complexes with Li(+) and 1-ethyl-3-methylimidazolium cation (emim(+)) were calculated at the MP2/6-311G** level. The E(form) values calculated for the Li[BF(4)], Li[BF(3)CF(3)], Li[BF(3)C(2)F(5)], Li[BF(3)C(3)F(7)], and Li[BF(3)C(4)F(9)] complexes were -144.1, -139.3, -137.4, -136.3, and -135.4 kcal/mol, respectively. The E(form) values calculated for the [emim][BF(4)], [emim][BF(3)CF(3)], [emim][BF(3)C(2)F(5)], [emim][BF(3)C(3)F(7)], and [emim][BF(3)C(4)F(9)] complexes were -85.2, -81.2, -79.7, -79.7, and -79.2 kcal/mol, respectively. The electrostatic interactions are the major source of the attraction in the complexes, whereas the contribution of the induction interactions to the attraction is not negligible. The interactions of the perfluoroalkyltrifluoroborate anions with Li(+) and emim(+) are substantially weaker than those of the BF(4)(-) because of the weaker electrostatic interactions. The analysis of the interactions suggests that the weaker interactions between the BF(3)CF(3)(-) and emim(+) compared with those between the BF(4)(-) and emim(+) are the cause of the lower viscosity of the [emim][BF(3)CF(3)] ionic liquid compared with the [emim][BF(4)] ionic liquid. The order of experimental self-diffusion coefficients of the cations and anions in the ionic liquids is BF(4)(-) < BF(3)CF(3)(-) approximately BF(3)C(2)F(5)(-) > BF(3)C(3)F(7)(-) > BF(3)C(4)F(9)(-), which is well reproduced by the molecular dynamic simulations. The analysis of the rotational relaxation of emim(+) suggests that the translational diffusion of cations and anions is associated with the rotational diffusion of emim(+).

Effects of dissolved water on Li+ solvation in 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ionic liquid studied by NMR.

(1)H and (7)Li NMR chemical shifts of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide-water solutions in the presence and absence of lithium bis(trifluoromethanesulfonyl)amide were determined at 293.2 K over a wide range of water concentrations from 0.0156 to 1.16 mol kg(-1). These results revealed the attractive interaction between water molecule and Li(+) as well as the hydrogen bonding among water molecules. Moreover, self-diffusion coefficients of water, 1-ethyl-3-methylimidazolium cation, Li(+), and bis(trifluoromethanesulfonyl)amide anion in the ionic liquid solutions at various water contents were determined by (1)H, (7)Li, and (19)F NMR techniques. It was found that Li(+) is averagely hydrated by eight water molecules in the ionic liquid solutions. Furthermore, (7)Li longitudinal relaxation times of Li(+) in the ionic liquid solutions at 293.2 K were measured with two different magnetic fields and various water contents. The mean one-jump distances of Li(+) in the ionic liquid solutions were estimated from the correlation times and the self-diffusion coefficients. A comparison between the hydrodynamic radius and the mean one-jump distance of Li(+) suggested the formation of water channels in the ionic liquid solutions.

Determination of anisotropic solvation structure of octafluorotoluene in supercritical carbon dioxide by means of solvent-induced 19F NMR chemical shift

Abstract 19 F NMR chemical shifts of octafluorotoluene and hexafluorobenzene in dilute carbon dioxide solutions were precisely determined at a fixed temperature of 314.4 K over a wide range of pressure from 1 to 35 MPa. We newly present the analytical procedure to determine anisotropic solvation structure by means of a solvent-induced 19 F NMR chemical shift. The anisotropic solvation structure around octafluorotoluene in supercritical carbon dioxide was discussed in comparison with a more symmetric geometry of hexafluorobenzene.

Effects of Tetrafluoroborate and Bis(trifluoromethylsulfonyl)amide Anions on the Microscopic Structures of 1-Methyl-3-octylimidazolium-Based Ionic Liquids and Benzene Mixtures: A Multiple Approach by ATR-IR, NMR, and Femtosecond Raman-Induced Kerr Effect Spectroscopy

The microscopic aspects of the two series of mixtures of 1-methyl-3-octylimidazolium tetrafluoroborate ([MOIm][BF4])-benzene and 1-methyl-3-octylimidazolium bis(trifluoromethylsulfonyl)amide ([MOIm][NTf2])-benzene were investigated by several spectroscopic techniques such as attenuated total reflectance IR (ATR-IR), NMR, and fs-Raman-induced Kerr effect spectroscopy (fs-RIKES). All three different spectroscopic results indicate that the anions more strongly interact with the cations in the [MOIm][BF4]-benzene mixtures than in the [MOIm][NTf2]-benzene mixtures. This also explains the different miscibility features between the two mixture systems well. The xC6H6 dependences of the chemical shifts and the C-H out-of-plane bending mode of benzene are similar: the changes are large in the high benzene concentration (xC6H6 > ∼ 0.6) compared to the low benzene concentration. In contrast, the linear xC6H6 dependences of the first moments of the low-frequency spectra less than 200 cm(-1) were observed in both the [MOIm][BF4]-benzene and [MOIm][NTf2]-benzene systems. The difference in the xC6H6 dependent features between the chemical shifts and intramolecular vibrational mode and the intermolecular/interionic vibrational bands might come from the different probing space scales. The traces of the parallel aromatic ring structure and the T-shape structure were found in the ATR-IR and NMR experiments, but fs-RIKES did not observe a clear trace of the local structure. This might imply that the interactions between the imidazolium and benzene rings are not strong enough to librate the imidazolium and benzene rings together. The bulk properties, such as miscibility, density, viscosity, and surface tension, of the two ionic liquid-benzene mixture series were also compared to the microscopic aspects.

SANS, ATR-IR, and 1D- and 2D-NMR studies of mixing states of imidazolium-based ionic liquid and aryl solvents

The mixing states of imidazolium-based ionic liquid, 1-dodecyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide (C12mim(+)TFSA(-)), and two aryl solvents toluene and α,α,α-trifluorotoluene (TFT) have been clarified on both meso- and microscopic scales using small-angle neutron scattering (SANS) and ATR-IR techniques. To elucidate the interactions between C12mim(+)TFSA(-) and aryl solvent molecules from the change in the electron densities of C12mim(+) and TFSA(-), 1D-NMR measurements for (1)H and (13)C atoms have been conducted on C12mim(+)TFSA(-)-aryl solvent solutions as a function of the aryl solvent mole fraction. In addition, the interactions between the dodecyl chain of C12mim(+) and aryl solvent molecules have been observed using 2D-NMR techniques of (1)H{(1)H} ROESY and (19)F{(1)H} HOESY. These results have been compared with those of benzene solutions previously investigated. The SANS measurements have shown that toluene is heterogeneously mixed with C12mim(+)TFSA(-) as well as benzene. However, the heterogeneity of the toluene solutions is slightly lower than that of the benzene solutions. In contrast, TFT is homogeneously mixed with the ionic liquid at least on the present SANS scale. The substituent effects of the three aryl solvent molecules of benzene, toluene, and TFT on the mixing states of the solutions have been discussed in terms of the cation-π interaction between the imidazolium and phenyl rings and the interaction between the dodecyl group and aryl solvent molecules.

Solvent-Dependent Properties and Higher-Order Structures of Aryl Alcohol + Surfactant Molecular Gels

Molecular organogels, comprising small organic gelators in solvents, can be applied for dispersal of optical devices, such as emitters. Phenolic compounds and the surfactant bis(2-ethylhexyl) sulfosuccinate (AOT) are known examples of self-assembly organogels. However, conventional phenol + AOT gels in aromatic and acyclic alkane solvents are optically turbid, which is an obstacle for use as host materials in optical devices. In this study, a variety of aryl alcohol-AOT-solvent sets have been investigated systematically, and the correlation between the molecular architecture and optical transparency of the gels was considered. Accordingly, p-chlorophenol + AOT gels in cyclic alkane solvents were shown to form optically transparent gels. In contrast, aromatic and acyclic alkane solvents gave rise to turbid or opaque gels, even when utilizing the same gelators. AFM, NMR, SAXS, and FTIR were employed to determine the organogel structures. Consequently, we found that the gel transparency strongly depends on the size of the fibrous network of the gel, the structure of which is attributed to higher-order aggregates of the gelators. The average contour length and diameter of the fibrous network, lav and dav, respectively, were determined from AFM images. The transparent gels were shown to have lav = 4-9 μm and dav ≤ 0.3 μm, whereas the turbid gels had lav = 15 μm and dav = 0.4-0.6 μm. Such differences in the size of the fibrous network significantly affected the mechanical response of the gels, as shown by stress-strain measurements.

Fluorination effects on rotational correlation times of tris(β-diketonato)aluminum(III) in CO2 by 27Al NMR relaxation measurements.

(27)Al NMR longitudinal relaxation times, T(1,obs)((27)Al), of [Al(acac)(3)] and [Al(hfa)(3)] (Hacac = acetylacetone, Hhfa = hexafluoroacetylacetone) in CH(3)CN and CO(2) were measured over a wide range of temperature and pressure. The rotational correlation times, τ(r), of the tris(β-diketonato)aluminum(III) complexes were determined from T(1,obs)((27)Al) using (27)Al quadrupole coupling constants, eQq/h((27)Al), which were also obtained to be 3.11 and 3.22 MHz for [Al(acac)(3)] and [Al(hfa)(3)], respectively, in CD(3)CN by the dual spin probe technique in the present study. At each temperature, τ(r) increased almost linearly with increasing viscosity, η, in both CH(3)CN and CO(2); however, τ(r) in CO(2) at near critical densities deviated appreciably upward, as shown in a similar analogue of bis(acetylacetonato)beryllium(II), [Be(acac)(2)] (Umecky; et al. J. Phys. Chem. B 2002, 106, 11114). The η/T dependence of τ(r) was examined to discuss intermolecular interactions between the complexes and solvent molecules in terms of the fluorination and geometrical effects. The degree of solute-solvent interactions increases in the order [Be(acac)(2)] < [Al(hfa)(3)] < [Al(acac)(3)] in CH(3)CN and [Al(acac)(3)] < [Be(acac)(2)] < [Al(hfa)(3)] in CO(2). The results suggest that dipolar CH(3)CN molecules interact with negatively charged oxygen atoms in the complexes, whereas nonpolar CO(2) prefers fluorinated substituents as well as quasi-aromatic rings in the ligands. Moreover, the relationship between the rotational and translational motions of tris(acetylacetonato)metal(III), [M(III)(acac)(3)], in CO(2) was investigated.