Yukihiro Yoshida

Room-Temperature Synthesis of Manganese Oxide Monosheets

Preparation of single-layer manganese oxide nanosheets (monosheets) comprised of edge-shared MnO(6) octahedra has relied on multistep processing involving a high-temperature solid-state synthesis of bulk templates, and ion-exchange and exfoliation reactions in solutions, requiring high cost and long processing time. Here we demonstrate the first single-step approach to directly access the MnO(2) monosheets, by the chemical oxidation of Mn(2+) ions in the presence of tetramethylammonium cations in an aqueous solution. Of importance is that this template-free reaction readily proceeds within a day at room temperature. The ability of the MnO(2) monosheets to self-assemble allows aggregation, to form layered structures with potassium cations and cationic tetrathiafulvalene analogues as intercalants. Furthermore, Langmuir-Blodgett (LB) films composed of the MnO(2) monosheets were successfully fabricated by the LB deposition method, in which about one layer of the monosheets was deposited for each process.

Influence of structural variations in 1-alkyl-3-methylimidazolium cation and tetrahalogenoferrate(III) anion on the physical properties of the paramagnetic ionic liquids

A series of paramagnetic ionic liquids, which are comprised of 1-alkyl-3-methylimidazolium RMI+ cation (R = Et, n-Bu, n-hexyl and n-octyl) and tetrahalogenoferrate(III) FeX4− anion (X = Cl and Br), were prepared, and the influence of structural variations such as changing the alkyl chain (R) length in the cation and substituting the halides (X) in the anion on their thermal behavior, infrared and ultraviolet-visible absorption spectra, density, viscosity, ionic conductivity and magnetic susceptibility was characterized. The elongation of the alkyl chain leads to a pronounced reduction of fluidity and ionic conductivity, and the replacement of chlorides with bromides likewise leads to a similar tendency toward ionic diffusion. It would seem that the ion association is less pronounced in the FeBr4 salts, which can be rationalized on the basis of the more significant nephelauxetic effect together with the lower molar concentration in the FeBr4 salts.

Surface tension measurements of highly conducting ionic liquids

The capillary rise method is used to measure the room temperature surface tension of several ionic liquids, selected mainly for their high electrical conductivity. They include salts based on the cations 1-ethyl-3-methylimidazolium (EMI+), 1-butyl-3-methylimidazolium (BMI+), and 1,3-dimethylimidazolium (DMI+), paired with anions such as GaCl4−, FeCl4−, C(CN)3−, N(CN)2−, SCN−, EtSO4−, BF4−, CF3SO3−, (CF3SO3)2N− (Tf2N−) and Au(CN)2−. The method consumes relatively little sample (<0.1 cm3) with measurement errors of 5%. Vacuum-dried samples are placed in the measurement cell under ambient (humid) air, but the meniscus is kept dry by a small flow of dry gas. Failure to dry the active interface leads to rapid contamination in the case of hydrophilic liquids, and to anomalously high surface tension. The highest surface tension measured (61 dyn cm−1) corresponds to DMI–N(CN)2.

Taylor cones of ionic liquids from capillary tubes as sources of pure ions: The role of surface tension and electrical conductivity

The emissions of Taylor cones from a wide range of ionic liquids (ILs) have been tested in vacuo in an attempt to identify what physical properties favor the purely ionic regime (PIR). This regime is well known in the case of Taylor cones of liquid metals. For nonmetallic liquids, it has been previously observed in conventional (capillary tube) electrospray sources at room temperature only for the room temperature molten salt (ionic liquid) EMI–BF4 (EMI=1-ethyl-3-methylimidazolium). A large number of other ILs and their mixtures have been studied here, most of which (but not all) are unable to reach the PIR at room temperature. Based on these results and additional theoretical considerations, strong support is assembled for the notion that the PIR is favored by ILs not only of high electrical conductivity but also of high surface tension. This hypothesis is confirmed by tests with three recently synthesized ILs, EMI–GaCl4, EMI–C(CN)3, and EMI–N(CN)2, all of which combine exceptional surface tension and el...

Paramagnetic transition metal complexes with a redox-active ligand: M(hfac)2(EDO-EDT-TTF-py)n; [M = CuII, n= 1, 2; M = MnII, n= 2]

Synthesis, crystal structures, electrochemical and physical properties of the new ligand, EDO-EDT-TTF-py (L1) [4,5-ethylenedioxy-4′,5′-(4-pyridylethylenedithio)tetrathiafulvalene], and the paramagnetic transition metal coordination complexes, M(hfac)2(EDO-EDT-TTF-py)2; M = CuII (2), MnII (3), and CuII(hfac)2(EDO-EDT-TTF-py) (4) are reported where hfac = hexafluoroacetylacetonato. Crystal data: (L1) triclinic system, space group P, a = 8.4060(3), b = 10.5093(3), c = 11.5318(5) A, α = 64.758(2), β = 86.923(2), γ = 72.444(2)°, V = 875.22(6) A3, Z = 2, 2 and 3 are isostructural (data for 3 are given in brackets), triclinic system, space group P, a = 7.1085(4) [7.1013(9)A], b = 11.1210(7) [11.111(2)A], c = 16.3628(11) A [16.346(3) A], α = 91.682(2) [91.662(6)], β = 91.014(3) [91.036(7)], γ = 93.547(3)° [93.651(6)°], V = 1290.3(1) A3 [1286.3(3) A3], Z = 1, (4) triclinic system, space group P, a = 9.2937(1), b = 15.1897(2), c = 24.3174(6) A, α = 92.461(1), β = 93.048(1), γ = 105.491(1)°, V = 3297.6(1) A3, Z = 4. In the compounds 2, 3 and 4, the ligand L1 is coordinated to the transition metals through the nitrogen atom of the pyridine group. In the crystal, the organic and inorganic layers are segregated. The arrangement of the organic layers is similar to the well known β phase in BEDT-TTF [bis(ethylenedithio)tetrathiafulvalene] charge transfer complexes, showing that the crystal packing is mainly governed by π–π stacking of the organic molecules. L1 is a TTF derivative and shows the electron donating ability with oxidation potential E1½ = +0.52 V versus SCE in benzonitrile. The same oxidation potentials were observed for complexes 2 and 3, indicating the negligible interactions between the ligands and the metals in solution.

Correlation between surface tension and void fraction in ionic liquids.

An effort to systematize published and new data on the surface tension gamma of ionic liquids (ILs) is based on the hypothesis that the dimensionless surface tension parameter gamma V v (2/3)/ kT is a function of the void fraction x v = V v/ V m. The void volume V v is defined as the difference between the liquid volume V m occupied by an ion pair (known from cationic and anionic masses and liquid density measurements) and the sum V (+) + V (-) of the cationic and anionic volumes (known from crystal structures), while kT is the thermal energy. Our hypothesis that gamma V m (2/3)/ kT = G( x v) is initially based on cavity theory. It is then refined based on periodic lattice modeling, which reveals that the number N of voids per unit cell (hence the dimensionless surface tension) must depend on x v. Testing our hypothesis against data for the five ILs for which surface tension and density data are available over a wide range of temperatures collapses all of these data almost on a single curve G( x v), provided that slight (4%) self-consistent modifications are introduced on published crystallographic data for V (+) and V (-). An attempt to correlate the surface tension vs temperature data available for inorganic molten salts is similarly successful, but at the expense of larger shifts on the published ionic radii (8.8% for K; 3.3% for I). The collapsed G( x v) curves for ILs and inorganic salts do not overlap anywhere on x v space, and appear to be different from each other. The existence of a relation between gamma and x v is rationalized with a simple capillary model minimizing the energy. Our success in correlating surface tension to void fraction may apply also to other liquid properties.

Ionic liquids based on diethylmethyl(2-methoxyethyl)ammonium cations and bis(perfluoroalkanesulfonyl)amide anions: influence of anion structure on liquid properties

A series of diethylmethyl(2-methoxyethyl)ammonium (DEME)-based ionic liquids were prepared using bis(perfluoroalkanesulfonyl)amide (C(n)F(2n+1)SO(2))(2)N anions with different perfluoroalkyl chain lengths (n = 0, 1, 2, 3, and 4), and the influence of the structural variation on their thermal, ion-diffusive (ionic conductivity and viscosity), ion-concentration (molar concentration and ion association), and solvatochromic (polarity and hydrogen-bond acceptor ability) properties was investigated. The elongation of the perfluoroalkyl chain causes the pronounced suppression of ionic conductivity, fluidity, and polarity. According to the crystallographic study of the corresponding (C(n)F(2n+1)SO(2))(2)N salts formed with high-symmetrical tetramethylammonium cations, the decreased ion diffusivity must be a consequence of the increased contribution of the interionic van der Waals interactions of FF type and hydrogen-bonding interactions of C-HF type in addition to C-HO type. The Kamlet-Taft π*-scale (polarity) is under the control of the ion concentration, associated with the perfluoroalkyl chain length in the anions. The larger Kamlet-Taft β-scale (hydrogen-bond acceptor ability) of DEME-based ionic liquids with a longer perfluoroalkyl chain appears to be responsible for the larger degree of ion association of oppositely charged ions, which was manifested in the Walden rule deviation.

Complex formation of ethylenedioxyethylenedithiotetrathiafulvalene (EDOEDT-TTF: EOET) and its self-assembling ability

36 kinds of donor(D)–acceptor(A) type charge transfer (CT) solids were prepared based on ethylenedioxyethylenedithiotetrathiafulvalene (EDOEDT-TTF or EOET), which is a hybrid molecule of bis(ethylenedioxy)-TTF (BEDO-TTF or BO) and bis(ethylenedithio)-TTF (BEDT-TTF or ET). A plot of the first CT absorption bands in solids against the difference in first redox potential between donor and acceptor molecules (ΔE) classified the complexes into five groups, A: highly conductive CT complexes with partial CT state and segregated stacks, B: partially ionic CT insulators with alternating stacks, C: essentially neutral clathrate complexes, D: neutral CT insulators with alternating stacks, and E: completely ionic insulators. Group A is spread out over an extensive ΔE range compared to one-dimensional organic metals such as the 1 ∶ 1 TTF–TCNQ system. This indicates that the EOET complexes among this group have a high electronic dimensionality arising from the self-aggregation of the EOET molecules in a fashion similar to the BO ones. However, the self-assembling ability of the EOET molecules is less pronounced than that of the BO ones, thereby giving a metal–insulator transition for many complexes among Group A. The reduced self-assembling ability also affords alternating stacks in (MeO)2TCNQ, BTDA-TCNQ (Group B) and p-iodanil (Group C) complexes. Two structurally distinct complexes were prepared with spherical C60 (Group D), one containing concave EOET molecules and one-dimensional C60 columns, and the other planar EOET and two-dimensional C60 layers. The F4TCNQ complex (Group E) exhibits an antiferromagnetic ordering below 7 K, which is intermediate between those in (BO)(F4TCNQ) (5.4 K) and (ET)(F4TCNQ) (14 K).

Effect of liquid properties on electrosprays from externally wetted ionic liquid ion sources

Ionic liquid ion sources (ILISs) are externally wetted and electrochemically etched and sharpened tungsten tips used as electrospraying sources for ionic liquids in a vacuum. They have recently shown an ability to operate as emitters of pure ion beams (no drops), even with ionic liquids of moderate surface tension (γ<40dyn∕cm) and electrical conductivity (K<1S∕m) that had in all prior reports (all based on conventional internally fed capillary tips) always operated in the mixed ion-drop regime. The present study uses time of flight mass spectrometry to analyze full ion beams emitted from ILISs for a diversity of ionic liquids with properties in the wide range 0.26<K(S∕m)<2.8, 39.3<γ(dyn∕cm)<48.6. Remarkably, all liquids tested achieve the purely ionic regime. The main effect of reducing electrical conductivity is a reduction of the emission current from 180to10nA.

Dicyanoaurate(I) salts with 1-alkyl-3-methylimidazolium: luminescent properties and room-temperature liquid forming

Room-temperature ionic liquids containing dicyanoaurate(I) anions were prepared utilizing 1-alkyl-3-methylimidazolium cations, and display luminescence possibly due to the oligomerization of the significant fraction of Au(CN)2 anions in the liquids.