Yasuo Kameda

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 0.2-0.4 Å(-1), indicating the heterogeneity of their ionic liquids. SANS profiles I(H)(Q) and I(D)(Q) for the normal and the alkyl group deuterated ionic liquids, respectively, showed significant peaks for n = 10 and 12 without no form factor component for large spherical or spheroidal aggregates like micelles in solution. The peaks for n = 10 and 12 evidently disappeared in the difference SANS profiles ΔI(Q) [=I(D)(Q) - I(H)(Q)], although that for n = 12 slightly remained. This suggests that the long-range correlations originated from the alkyl groups hardly contribute to the low-Q peak intensity in SANS. To reveal molecular origin of the low-Q peak, we introduce here a new function; x-ray structure factor intensity at a given Q as a function of r, S(Q) (peak)(r). The S(Q) (peak)(r) function suggests that the observed low-Q peak intensity depending on n is originated from liquid structures at two r-region of 5-8 and 8-15 Å for all ionic liquids examined except for n = 12. Atomistic MD simulations are consistent with the HEXRD and SANS experiments, and then we discussed the relationship between both variations of low-Q peak and real-space structure with lengthening the alkyl group of the C(n)mIm.

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. Experimentally evaluated S(Q(peak))(r(max)) functions, which represent the S(Q) intensity at a peak position of maximum intensity Q(peak) as a function of distance (actually a integration range r(max)), revealed that characteristic peaks in the low Q region are related to the intermolecular anion-anion correlation decrease in the r range of 10-12 Å. Appearance of the peak in the low Q region is probably related to the exclusion of the correlations among ions of the same sign in this r range by the alkyl chain aggregation. From MD simulations, we found unique and rather distorted NH···O hydrogen bonding between C(n)Am(+) (n = 2, 3, and 4) and NO(3)(-) in these ionic liquids regardless of the alkyl chain length. Subsequent ab initio calculations for both a molecular complex C(2)H(5)NH(2)···HONO(2) and an ion pair C(2)H(5)NH(3)(+)···ONO(2)(-) revealed that such distorted hydrogen bonding is specific in a liquid state of this family of ionic liquids, though the linear orientation is preferred for both the N···HO hydrogen bonding in a molecular complex and the NH···O one in an ion pair. Finally, we propose our interpretation of structural heterogeneity in PILs and also in APILs.

Liquid Structure of and Li + Ion Solvation in Bis(trifluoromethanesulfonyl)amide Based Ionic Liquids Composed of 1-Ethyl-3-methylimidazolium and N-Methyl-N-propylpyrrolidinium Cations

Liquid structures of the bis(trifluoromethanesulfonyl)amide based ionic liquids composed of 1-ethyl-3-methylimidazolium and N-methyl-N-propylpyrrolidinium ([C(2)mIm(+)][TFSA(-)] and [C(3)mPyrro(+)][TFSA(-)], respectively) and Li(+) ion solvation structure in their lithium salt solutions were studied by means of high-energy X-ray diffraction (HEXRD) technique with the aid of MD simulations. With regard to neat ionic liquids, a small but significant difference was found at around 3.5 Å in the intermolecular radial distribution functions G(inter)(r)s for these two ionic liquids; i.e., G(inter)(r) for [C(2)mIm(+)][TFSA(-)] was positioned at a slightly shorter region relative to that for [C(3)mPyrro(+)][TFSA(-)], which suggests that the nearest neighboring cation-anion interaction in the imidazolium ionic liquid is slightly greater than that in the other. With regard to Li(+) ion solvation structure, G(inter)(r)s for [C(2)mIm(+)][TFSA(-)] dissolving Li(+) ion exhibited additional small peak of about 1.9 Å attributable to the Li(+)-O (TFSA(-)) atom-atom correlation, though the corresponding peak was unclear in [C(3)mPyrro(+)][TFSA(-)] due to overlapping with the intramolecular atom-atom correlations in [C(3)mPyrro(+)]. In addition, the long-range density fluctuation observed in the neat ionic liquids diminished with the increase of Li(+) ion concentration for both ionic liquid solutions. These observations indicate that the large scale Li(+) ion solvated clusters are formed in the TFSA based ionic liquids, and well support the formation of [Li(TFSA)(2)](+) cluster clarified by previous Raman spectroscopic studies. MD simulations qualitatively agree with the experimental facts, by which the decrease in the long-range oscillation amplitude of r(2){G(r) - 1} for the Li(+) containing ionic liquids can be ascribed to the variation in the long-range anion-anion correlations caused by the formation of the Li(+) ion solvated clusters.

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. The values of Δ(iso)G° obtained are small (a few units of kJ/mol) and show a slight negative variation with the decrease of the size of the halide anion. On the other hand, Δ(iso)H° and Δ(iso)S° values are positive for [C(4)mim]I and decrease with the anion size to yield negative values for [C(4)mim]Cl and [C(4)mim]Br. This suggests that the negative electrostatic field around the halide anions stabilizes the gauche isomer from an enthalpic point of view. In order to study the structure and ion-ion interactions in this type of ionic liquids, high-energy X-ray diffraction experiments were performed for [C(4)mim]Cl at different temperatures and for supercooled [C(4)mim][Br] at ambient temperature. Molecular dynamics (MD) simulations for these systems were also carried out at several temperatures. Δ(iso)G° and Δ(iso)H° values derived from the simulations qualitatively agree with the experimental ones. Experimental X-ray structure factors are also well reproduced by the simulations. The MD results also allowed the calculation of different spatial distribution functions (SDFs) for the three ionic liquids. Although all SDFs exhibit similar trends, [C(4)mim]I shows a reduced anion density facing the C(2)-H atoms of the cation and enhanced anion densities above and below the imidazolium ring plane. This indicates that anions localized near the C(2)-H atoms of the cation can stabilize their gauche conformer, an effect that is stronger with smaller anions. This conclusion is also supported by ab initio calculations at the CCSD(T) level for isolated ion pairs.

Synthesis and electrochemistry of double-decker lanthanoid (III) phthalocyanine complexes

Abstract The synthesis, spectroscopy and electrochemistry of double-decker lanthanoid phthalocyanine complexes Li[(Pc)Ln(Pc)] (Ln represents trivalent ions of La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu and Pc are the divalent anions of phthalocyanine) are reported. These complexes were obtained by new synthesis methods.

Thermally induced crystallization of amorphous Ge0.4Se0.6

Abstract The Raman scattering measurement in amorphous Ge0.4Se0.6 was carried out at several temperatures below 440°C in order to investigate the relation in short range order between amorphous and crystalline phases. Raman spectra were obtained using 514.5 nm argon-ion laser and a double grating monochrometer. The 175 and 280 cm−1 vibrational modes in amorphous Ge0.4Se0.6 disappear after the complete crustallization, indicating that the chemical order including Ge-Ge bonds is characteristic to the amorphous phase but not to the crystalline one. This agrees with theresult by previous radial distribution studies that amorphous GexSe1−x alloys with x > 1 3 have a different local order from the crystalline form. The A1 mode peak of GeSe4 tetrahedron units alters its position on heating. Therefore, it may be considered that intra- and inter-molecular interactions of this unit change through the crystallization process.

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. The free energy of CIP formation is not simply governed by the solvent dielectric constant, and microscopic analyses of solute-solvent interaction at a molecular level are then performed from energetic and structural viewpoints. Vacant sites of Li(+) cation in CIP are solvated with three carbonyl oxygen atoms of PC and DMC solvent molecules, and the solvation is stronger for the monodentate CIP than for the multidentate. Energetically favorable solute-solvent configurations are shown to be spatially more restricted for the multidentate CIP, leading to the observation that the solvent favors the monodentate coordination structure.

Short-range order in amorphous Ge(Se1−xSx)2

Abstract X-ray diffraction in combination with the Raman scattering measurement in amorphous Ge(Se 1− x S x ) 2 was conducted on a range of compositions. The first peak in the distribution function, g ( r ), is well resolved in all compositions and gives roughly four as the Ge coordination number, assuming that the peak contains only GeSe and GeS contributions, but not SeSe, SeS or SS contributions. This result indicates that these glasses are all formed by mixed-anion AX 4− n Y n tetrahedral units ( n = 0–4). The Raman symmetric stretching frequencies of five tetrahedral units observed in the spectra were determined on the basis of the VFF analysis to be 201 cm −1 for GeSe 4 , 225 cm −1 for GeSe 3 S 1 , 233 and 245 cm −1 for GeSe 1 S 3 and 345 cm −1 for GeS 4 units.

Inelasticity Effect on Neutron Scattering Intensities of the Null-H2O

Time-of-flight (TOF) neutron scattering measurements have been carried out for liquid null-H2O, in which the average coherent scattering length of hydrogen atoms is zero. In order to determine the inelasticity effect depending on both the scattering angle and the neutron flight path ratio, γ [ = l_{s}/(l_{0} + l_{s}), l 0 and l s denote the moderator-sample and sample-detector distances, respectively], neutron scattering measurements have been performed using three neutron spectrometers, HIT-II, RAT, and SWAN, installed at KENS, Tsukuba, Japan. The self-scattering intensity for the null-H2O was derived by subtracting the known O–O partial structure factor from the observed scattering cross-section. It has been revealed that the magnitude of the inelasticity distortion involved in the self-scattering term is still significant even at a smaller scattering angle than that expected from the first-order inelasticity correction formulas proposed in the literature. The inelasticity distortion in the self-scatter...

Li+ Local Structure in Hydrofluoroether Diluted Li-Glyme Solvate Ionic Liquid

Hydrofluoroethers have recently been used as the diluent to a lithium battery electrolyte solution to increase and decrease the ionic conductivity and the solution viscosity, respectively. In order to clarify the Li(+) local structure in the 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (HFE) diluted [Li(G4)][TFSA] (G4, tetraglyme; TFSA, bis(trifluoromethanesulfonyl)amide) solvate ionic liquid, Raman spectroscopic study has been done with the DFT calculations. It has turned out that the HFE never coordinates to the Li(+) directly, and that the solvent (G4) shared ion pair of Li(+) with TFSA anion (SSIP) and the contact ion pair between Li(+) and TFSA anion (CIP) are found in the neat and HFE diluted [Li(G4)][TFSA] solvate ionic liquid. It is also revealed that the two kinds of the CIP in which TFSA anion coordinates to the Li(+) in monodentate and bidentate manners (hereafter, we call them the monodentate CIP and the bidentate CIP, respectively) exist with the SSIP of predominant [Li(G4)](+) ion-pair species in the neat [Li(G4)][TFSA] solvate ionic liquid, and that the monodentate CIP decreases as diluting with the HFE. To obtain further insight, X-ray total scattering experiments (HEXTS) were carried out with the aid of MD simulations, where the intermolecular force field parameters, mainly partial atomic charges, have been newly proposed for the HFE and glymes. A new peak appeared at around 0.6-0.7 Å(-1) in X-ray structure factors, which was ascribed to the correlation between the [Li(G4)][TFSA] ion pairs. Furthermore, MD simulations were in good agreement with the experiments, from which it is suggested that the terminal oxygen atoms of the G4 in [Li(G4)](+) solvated cation frequently repeat coordinating/uncoordinating to the Li(+), although almost all of the G4 coordinates to the Li(+) to form [Li(G4)](+) solvated cation in the neat and HFE diluted [Li(G4)][TFSA] solvate ionic liquid.