Large-angle X-ray Scattering Research Articles

Structure of Aqueous Scandium(III) Nitrate Solution by Large-Angle X-ray Scattering Combined with Empirical Potential Refinement Modeling, X-ray Absorption Fine Structure, and Discrete Variational Xα Calculations

Abstract Large-Angle X-ray scattering (LAXS) and Sc K X-ray absorption near-edge structure (XANES) measurements are made at room temperature on a 1 M (= mol dm−3) Sc(NO3)3 aqueous solution. The X-ray interference function is subjected to an empirical potential structure refinement (EPSR) modeling to extract the site-site pair correlation functions, the coordination number distribution, and the spatial density functions (three-dimensional structure). The LAXS analysis combined with EPSR reveals that Sc3+ is surrounded by six or seven water molecules and one oxygen atom of NO3− with an Sc3+-Ow (H2O) and Sc3+-ON (NO3−) distance of 2.14 Å. NO3− has a weak solvation shell with a broad distribution of coordination numbers with the highest population of nine at an N-Ow distance of 3.66 Å. Solvent water forms the tetrahedral network structure. The XANES spectrum is compared with simulated spectra on various coordination geometries of an ScO7 moiety with a discrete variational Xα (DV-Xα) molecular orbital (MO) method. A distorted monocapped trigonal prism structure of Sc3+ best reproduced the experimental pre-peak due to the Sc 1s → 3d transition in the XANES spectrum.

Ionic liquids enhanced performance of PVC gels actuator

AbstractStimulated devices are highly demanded for actuators and artificial muscles in the recent era but susceptible to low deformation at an applied voltage. In the present work, ionic liquids (ILs) based gel films were prepared from the polyvinyl chloride (PVC), dibutyl adipate (DBA), 1‐butyl, 3‐methimidazolium chloride, and 1‐pentyl‐3‐methylimidazolium hexafluorophosphate by a simple solvent evaporation method. The structural, morphological, optical, and mechanical properties of the composite PVC/ILs gel were characterized by Fourier‐transform infrared spectroscopy (FTIR), Large Angle X‐ray scattering (LAXS), UV–visible (UV–vis) absorption spectroscopy, scanning electron micrpscopy (SEM) and elemental mapping. We found that the displacement of plasticized PVC gels‐based actuator was 0.1 mm with the response time of 0.33 s at an induced voltage of 1000 V. The loading of 0.02% of IL (fluorides) with PVC gel showed maximum deformation of 0.16 mm with a relatively rapid response time of 0.2 s. These high deformation and response time values of IL fluoride‐based gels are dramatically higher than reported PVC gels. Likewise, the loading of IL fluorides in the PVC gel showed a high elongation value at the break of about 377%. This work suggests that the flexible gel based on IL fluorides and PVC could be a potential candidate for the fabrication of high‐performance artificial muscles and tunable soft actuators.

Elusive Coordination of the Ag+ Ion in Aqueous Solution: Evidence for a Linear Structure.

X-ray absorption spectroscopy (XAS) has been employed to study the coordination of the Ag+ ion in aqueous solution. The conjunction of extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) data analysis provided results suggesting the preference for a first shell linear coordination with a mean Ag-O bond distance of 2.34(2) Å, different from the first generally accepted tetrahedral model with a longer mean Ag-O bond distance. Ab initio molecular dynamics simulations with the Car-Parrinello approach (CPMD) were also performed and were able to describe the coordination of the hydrated Ag+ ion in aqueous solution in very good agreement with the experimental data. The high sensitivity for the closest environment of the photoabsorber of the EXAFS and XANES techniques, together with the long-range information provided by CPMD and large-angle X-ray scattering (LAXS), allowed us to reconstruct the three-dimensional model of the coordination geometry around the Ag+ ion in aqueous solution. The obtained results from experiments and theoretical simulations provided a complex picture with a certain amount of water molecules with high configurational disorder at distances comprised between the first and second hydration spheres. This evidence may have caused the proliferation of the coordination numbers that have been proposed so far for Ag+ in water. Altogether these data show how the description of the hydration of the Ag+ ion in aqueous solution can be complex, differently from other metal species where hydration structures can be described by clusters with well-defined geometries. This diffuse hydration shell causes the Ag-O bond distance in the linear [Ag(H2O)2]+ ion to be ca. 0.2 Å longer than in isolated ions in solid state.

Hydration of Oxometallate Ions in Aqueous Solution.

The strength of hydrogen bonding to and structure of hydrated oxometallate ions in aqueous solution have been studied by double difference infrared (DDIR) spectroscopy and large-angle X-ray scattering (LAXS), respectively. Anions are hydrated by accepting hydrogen bonds from the hydrating water molecules. The oxygen atom of the permanganate and perrhenate ions form weaker and longer hydrogen bonds to water than the hydrogen bonds in bulk water (i.e., they act as structure breakers), while the oxygen atoms of the chromate, dichromate, molybdate, tungstate, and hydrogenvanadate ions form hydrogen bonds stronger than those in bulk water (i.e., they act as structure makers). The oxometallate ions form one hydration shell distinguishable from bulk water as determined by DDIR spectroscopy and LAXS. The hydration of oxoanions results in X–O bond distances ca. 0.02 Å longer than those in unsolvated ions in the solid state not involved in strong bonding to counterions. The oxygens of oxoanions with a central atom from the second and third series in the periodic table and the hydrogenvanadate ion hydrogen bind three hydrating water molecules, while oxygens of oxoanions with a heavier central atom only form hydrogen bonds to two water molecules.

A low transition temperature mixture for the dispersive liquid-liquid microextraction of pesticides from surface waters

This paper illustrates the development of a procedure based on the use of a low transition temperature mixture (LTTM) for the dispersive liquid-liquid microextraction (DLLME) of fungicides, insecticides and acaricides from surface waters. The LTTM preparation involves the heat-mixing of choline chloride and acetylsalicylic acid in a molar ratio 1:2 (ChCl(ASA)2). The resulting mixture appears as a clear viscous liquid at room-temperature, denser than water (1.20 ± 0.01 g mL−1). For its characterization, differential scanning calorimetry (DSC) provided crucial evidence to classify it as a LTTM rather than as a deep eutectic solvent (DES) since it revealed an intense glass transition at −37 °C. Large-angle X-ray scattering (LAXS) confirmed the lack of any long-distance order. Due to the LTTM immiscibility with water, an evaluation study was carried out to test ChCl(ASA)2 as an effective alternative to the conventional chlorinated solvents for DLLME. To this end, 24 pesticides were used as model compounds, extracted from surface water samples (5 mL) and analyzed by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The definitive procedure required the optimization of some key parameters such as volume of extracting solvent, type and volume of dispersing solvent, volume of the aqueous sample, LTTM dispersion procedure, and extraction time. Depending on pKa and logP values, recoveries ranged from 18 (for very polar compounds) to 96%, revealing that the ideal candidates for the extraction with ChCl(ASA)2 are neutral compounds with logP >2. After complete validation, the method was applied to analyze water samples from the River Tiber where dodine and dimetomorph were found at low μg L−1 concentration levels.

Structure Determination of Phosphoric Acid and Phosphate Ions in Aqueous Solution Using EXAFS Spectroscopy and Large Angle X-ray Scattering.

The structures of hydrated phosphoric acid and phosphate ions (H2PO4-, HPO42-, and PO43-) in aqueous solution have been determined by P K-edge EXAFS and large angle X-ray scattering (LAXS). The P-O bond distance in all phosphate species studied is close to 1.53 Å. The P-(O)···Oaq distances have been refined to ca. 3.6 Å from the LAXS data giving a P-O···Oaq bond angle close to tetrahedral, suggesting that each oxygen or OH group of phosphoric acid and dihydrogen phosphate, on average, hydrogen bind three water molecules. The (P-)O(-H)···Oaq and (P-)O···(H-)Oaq hydrogen bonds in hydrated phosphoric acid and the H2PO4- ion are shorter than the hydrogen bonds in neat water. This supports previous infrared spectroscopic studies claiming that the hydrogen bonds in hydrated phosphoric acid and phosphate ions are stronger than the hydrogen bonds in neat water. Phosphoric acid and phosphate ions can therefore be regarded as structure making solutes. This is the first study applying transmission mode X-ray absorption spectroscopy (XAS) data collection on the P K-edge. It shows that XAS spectra collected in transmission mode have a much better S/N ratio than data collected in fluorescence mode, allowing accurate determination of P-O bond distances. Furthermore, P K-edge EXAFS data collected in fluorescence mode display a higher amplitude at high k than expected due to increasing radiated volume of the sample with increasing energy as the total absorption decreases sharply with increasing energy of the X-rays. As a result, the fluorescence signal becomes nonproportional to the intensity of the X-ray beam over the EXAFS spectrum. This results in an increasing amplitude of the EXAFS function with increasing energy of the X-ray beam resulting in too small Debye-Waller coefficients.

Studies of glass structure in the system Bi2O3-B2O3-SiO2

The structure of single-phase glass in the Bi2O3-B2O3-SiO2 system has been investigated by the method of large angle X-ray scattering (LAXS). The glass of two-component systems Bi2O3-B2O3 and Bi2O3-SiO2 and those of compositions in three sections with the Bi2O3 content varying from 20 to 80 mol % at B2O3: SiO2 ratios equal to 3, 1, and 1/3 have been studied. The LAXS data indicate the existence of the structural ordering beyond the first coordination spheres in glass of the Bi2O3-B2O3-SiO2 system. Three clearly expressed diffraction maxima on LAXS angle dependences are caused by the presence of repeating interatom distances in the structure of the short- and intermediate-range order. This results from the formation of structural groups with the participation of modifier ions and, consequently, ordering in the boron-silica surrounding of the bismuth ions. A partial crystallization is observed on the cooling of the melts containing 50% Bi2O3 in the Bi2O3-SiO2 system and 80% Bi2O3 in the Bi2O3-B2O3 system. The area of liquid phase separation is formed at the Bi2O3 content of less than 30 %. The structure of the glass under study corresponds to the model of associated ideal solutions, which is a partial case of the generalized lattice theory of associated solutions.

A structural study of D-mannitolatodimolybdate(VI) complexes in aqueous solution

The structure of the D-mannitolatodimolybdate(VI) complex has been determined by means of large angle X-ray scattering (LAXS) in aqueous solution at two pH values, 2.0 and 5.5. The two complexes have in principle the same structure in aqueous solution, two face-sharing molybdate(VI) octahedra connected to one D-mannitol ligand, as previously observed in the solid state. In the deprotonated form of the complex, pH 5.5, the D-mannitol ligand has lost a proton and as a result the Mo⋅⋅⋅Mo distance is 0.054Å shorter than the protonated form, pH 2.0. This indicates that it is a proton on an oxygen shared by molybdate groups that leaves the complex at deprotonation and forces the molydate(VI) octahedra even closer to each other.

On the Structure and Volumetric Properties of Solvated Lanthanoid(III) Ions in Amide Solutions

The coordination chemistry and the volumetric properties of three representative lanthanoid(III) ions--lanthanum(III), gadolinium(III), and lutetium(III)--have been studied in three amide solvents with gradually increasing spatial demand upon coordination: N,N-dimethylformamide (dmf) < N,N-dimethylacetamide (dma) < N,N-dimethylpropionamide (dmp). Large angle X-ray scattering (LAXS) and EXAFS have been used to determine the structure of the solvated lanthanoid(III) ions in solution, further supplemented with a crystallographic study on octakis(N,N-dimethylacetamide)lanthanum(III) triflate, [La(dma)8](CF3SO3)3. The selection of ions and solvents allows an estimate of the steric congestion effects on the resulting coordination number, CN, ranging from nine for lanthanum(III) ions in dmf to seven for the smaller lutetium(III) ion in space-demanding dma. The standard partial molar volumes of the solvated lanthanoid(III) ions in water and dmf are reflected in the CNs, as these solvent molecules are small enough to not interfere with each other upon coordination. However, the larger and more space-demanding dma displays a different pattern with an almost constant standard partial molar volume and a decreasing CN, counterbalancing the difference in ionic radius of the lanthanoid(III) ion.

A coordination chemistry study of hydrated and solvated cationic vanadium ions in oxidation states +III, +IV, and +V in solution and solid state.

The coordination chemistry of hydrated and solvated vanadium(III), oxovanadium(IV), and dioxovanadium(V) ions in the oxygen-donor solvents water, dimethyl sulfoxide (DMSO), and N,N'-dimethylpropyleneurea (DMPU) has been studied in solution by extended X-ray absorption fine structure (EXAFS) and large-angle X-ray scattering (LAXS) and in the solid state by single-crystal X-ray diffraction and EXAFS. The hydrated vanadium(III) ion has a regular octahedral configuration with a mean V-O bond distance of 1.99 Å. In the hydrated and DMSO-solvated oxovanadium(IV) ions, vanadium binds strongly to an oxo group at ca. 1.6 Å. The solvent molecule trans to the oxo group is very weakly bound, at ca. 2.2 Å, while the remaining four solvent molecules, with a mean V-O bond distance of 2.0 Å, form a plane slightly below the vanadium atom; the mean O═V-O(perp) bond angle is ca. 98°. In the DMPU-solvated oxovanadium(IV) ion, the space-demanding properties of the DMPU molecule leave no solvent molecule in the trans position to the oxo group, which reduces the coordination number to 5. The O═V-O bond angle is consequently much larger, 107°, and the mean V═O and V-O bond distances decrease to 1.58 and 1.97 Å, respectively. The hydrated and DMSO-solvated dioxovanadium(V) ions display a very distorted octahedral configuration with the oxo groups in the cis position with a mean V═O bond distance of 1.6 Å and a O═V═O bond angle of ca. 105°. The solvent molecules trans to the oxo groups are weakly bound, at ca. 2.2 Å, while the remaining two have bond distances of 2.02 Å. The experimental studies of the coordination chemistry of hydrated and solvated vanadium(III,IV,V) ions are complemented by summarizing previously reported crystal structures to yield a comprehensive description of the coordination chemistry of vanadium with oxygen-donor ligands.

Small- and Large-angle X-ray Scattering Studies of Nanometer-order Sulfuric Acid Solution in Carbon Micropores

Abstract The structure of nanometer-order sulfuric acid solution in carbon micropores is investigated by large- and small-angle X-ray scattering experiments. The electron radial distribution function of the nanosolution is different from that of bulk solution. The intermolecular structure of nanosolution does not change with fractional filling. These results and the dependency of density fluctuations of the system with fractional filling showed that the nanometer-order sulfuric acid solutions in carbon micropores form a small molecular assembly with a hydration structure at low fractional filling.

A Study of the Hydration of the Alkali Metal Ions in Aqueous Solution

The hydration of the alkali metal ions in aqueous solution has been studied by large angle X-ray scattering (LAXS) and double difference infrared spectroscopy (DDIR). The structures of the dimethyl sulfoxide solvated alkali metal ions in solution have been determined to support the studies in aqueous solution. The results of the LAXS and DDIR measurements show that the sodium, potassium, rubidium and cesium ions all are weakly hydrated with only a single shell of water molecules. The smaller lithium ion is more strongly hydrated, most probably with a second hydration shell present. The influence of the rubidium and cesium ions on the water structure was found to be very weak, and it was not possible to quantify this effect in a reliable way due to insufficient separation of the O–D stretching bands of partially deuterated water bound to these metal ions and the O–D stretching bands of the bulk water. Aqueous solutions of sodium, potassium and cesium iodide and cesium and lithium hydroxide have been studied by LAXS and M–O bond distances have been determined fairly accurately except for lithium. However, the number of water molecules binding to the alkali metal ions is very difficult to determine from the LAXS measurements as the number of distances and the temperature factor are strongly correlated. A thorough analysis of M–O bond distances in solid alkali metal compounds with ligands binding through oxygen has been made from available structure databases. There is relatively strong correlation between M–O bond distances and coordination numbers also for the alkali metal ions even though the M–O interactions are weak and the number of complexes of potassium, rubidium and cesium with well-defined coordination geometry is very small. The mean M–O bond distance in the hydrated sodium, potassium, rubidium and cesium ions in aqueous solution have been determined to be 2.43(2), 2.81(1), 2.98(1) and 3.07(1) Å, which corresponds to six-, seven-, eight- and eight-coordination. These coordination numbers are supported by the linear relationship of the hydration enthalpies and the M–O bond distances. This correlation indicates that the hydrated lithium ion is four-coordinate in aqueous solution. New ionic radii are proposed for four- and six-coordinate lithium(I), 0.60 and 0.79 Å, respectively, as well as for five- and six-coordinate sodium(I), 1.02 and 1.07 Å, respectively. The ionic radii for six- and seven-coordinate K+, 1.38 and 1.46 Å, respectively, and eight-coordinate Rb+ and Cs+, 1.64 and 1.73 Å, respectively, are confirmed from previous studies. The M–O bond distances in dimethyl sulfoxide solvated sodium, potassium, rubidium and cesium ions in solution are very similar to those observed in aqueous solution.

Clusters of Imidazolium-Based Ionic Liquid in Benzene Solutions

Cluster formation of 1-dodecyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide (C(12)mim(+)TFSA(-)) in benzene solutions was investigated using small-angle neutron scattering (SANS), NMR, attenuated total reflectance infrared (ATR-IR), and large-angle X-ray scattering (LAXS) techniques. The SANS measurements revealed that C(12)mim(+)TFSA(-) is heterogeneously mixed with benzene in the narrow range of benzene mole fraction 0.9 ≤ x(C6D6) ≤ 0.995 with a maximum heterogeneity at x(C6D6) ≈ 0.99. The NMR results suggested that the imidazolium ring is sandwiched between benzene molecules through the cation-π interaction. Moreover, TFSA(-) probably interacts with the imidazolium ring even in the range of x(C6H6) ≥ 0.9. Thus, the imidazolium rings, benzene molecules, and TFSA(-) would form clusters in the C(12)mim(+)TFSA(-)-benzene solutions. The LAXS measurements showed that the distance between the imidazolium ring and benzene is ∼3.8 Å with that between the benzene molecules of ∼7.5 Å. On the basis of these results, we discussed a plausible reason for the liquid-liquid equilibrium of the C(12)mim(+)TFSA(-)-benzene system.

Coordination Chemistry Study of Hydrated and Solvated Lead(II) Ions in Solution and Solid State

The coordination chemistry of lead(II) in the oxygen donor solvents water, dimethylsulfoxide (dmso, Me(2)SO), N,N-dimethylformamide (dmf), N,N-dimethylacetamide (dma), N,N'-dimethylpropyleneurea (dmpu), and 1,1,3,3-tetramethylurea (tmu), as well as in the sulfur donor solvent N,N-dimethylthioformamide (dmtf), has been investigated by extended X-ray absorption fine structure (EXAFS) and/or large angle X-ray scattering (LAXS) in solution, and by single crystal X-ray diffraction and/or EXAFS of solid hydrates and solvates. Lead(II) may either form hemidirected complexes with large bond distance distribution and an apparent gap for excess electron density, or holodirected ones with a symmetric coordination sphere with normal bond distance distribution, depending on the strength of antibonding lead 6s/ligand np molecular orbital interactions and ligand-ligand interactions. The crystallographic data show that the solid lead(II) perchlorate and trifluoromethanesulfonate hydrate structures are hemidirected, while the solid lead(II) solvates of dma and dmpu have regular octahedral configuration with holodirected geometry and mean Pb-O bond distances in the range 2.50-2.52 Å. EXAFS data on the hydrated lead(II) ion in aqueous solution show broad bond distance distribution and a lack of inner-core multiple scattering contributions strongly indicating a hemidirected structure. The Pb-O bond distances found both by EXAFS and LAXS, 2.54(1) Å, point to a six-coordinate hydrated lead(II) ion in hemidirected fashion with an unevenly distributed electron density. The results obtained for the dmso solvated lead(II) ion in solution are ambiguous, but for the most part support a six-coordinate hemidirected complex. The mean Pb-O bond distances determined in dmf and dma solution by LAXS, 2.55(1) and 2.48(1) Å, respectively, indicate that in both solvate complexes lead(II) binds six solvent molecules with the former complex being hemidirected whereas the latter is holodirected. The dmpu and tmu solvated lead(II) ions have a regular holodirected octahedral configuration, as expected given their space-demanding characteristics and ligand-ligand intermolecular interactions. The dmtf solvated lead(II) ion in solution is most likely five-coordinate in a hemidirected configuration, with a mean Pb-S bond distance of 2.908(4) Å. New and improved ionic radii for the lead(II) ion in 4-8-coordination in hemi and holodirected configurations are proposed using crystallographic data.

Hydration and Hydrolysis of Thorium(IV) in Aqueous Solution and the Structures of Two Crystalline Thorium(IV) Hydrates

Solid octaaqua(kappa(2)O-perchlorato)thorium(IV) perchlorate hydrate, [Th(H(2)O)(8)(ClO(4))](ClO(4))(3).H(2)O, 1, and aquaoxonium hexaaquatris(kappaO-trifluoromethanesulfonato)thorium(IV) trisaquahexakis(kappaO-trifluoromethanesulfonato)thorinate(IV), H(5)O(2)[Th(H(2)O)(6)(OSO(2)CF(3))(3)][Th(H(2)O)(3)(OSO(2)CF(3))(6)], 2, were crystallized from concentrated perchloric and trifluoromethanesulfonic acid solutions, respectively. 1 adopts a severely distorted tricapped trigonal prismatic configuration with an additional oxygen from the perchlorate ion at a longer distance. 2 consists of individual hexaaquatris(kappaO-trifluoromethanesulfonato)thorium(IV) and trisaquahexakis(kappaO-trifluoromethanesulfonato)thorinate(IV) ions and an aquaoxonium ion bridging these two ions through hydrogen bonding. The hydrated thorium(IV) ion is nine-coordinated in aqueous solution as determined by extended X-ray absorption fine structure (EXAFS) and large angle X-ray scattering (LAXS). The LAXS studies also showed a second hydration sphere of about 18 water molecules, and traces of a 3rd hydration sphere. Structural studies in aqueous solution of the hydrolysis products of thorium(IV) have identified three different types of hydrolysis species: a mu(2)O-hydroxo dimer, [Th(2)(OH)(2)(H(2)O)(12)](6+), a mu(2)O-hydroxo tetramer, [Th(4)(OH)(8)(H(2)O)(16)](8+), and a mu(3)O-oxo hexamer, [Th(6)O(8)(H(2)O)(n)](8+). Detailed structures of these three hydrolysis species are given. A compilation of reported solid state structures of actinoid(IV) compounds with oxygen donor ligands show a strong correlation between the An-O bond distance and the coordination number. The earlier reported U-O bond distance in the hydrated uranium(IV) ion in aqueous solution, confirmed in this study, is related to nine-coordination. The hydrated tri- and tetravalent actinoid ions in aqueous solution all seem to be nine-coordinated. The trivalent ions show a significant difference in bond distance to prismatic and capping water molecules in assumed tricapped trigonal prismatic configuration, while the tetravalent ions seem to form more regular structures, probably because of higher polarization.

Effect of Methylation at the C2 Position of Imidazolium on the Structure of Ionic Liquids Revealed by Large Angle X-ray Scattering Experiments and MD Simulations

Abstract Liquid structures of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide [BMI+][TFSA−] and 1-butyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)amide [BDMI+][TFSA−] were studied by large-angle X-ray scattering (LAXS) experiments to elucidate methyl substitution effect at the C2 position of imidazolium cation on the long-range ordering of the ionic liquids. Radial distribution functions for both ionic liquids showed that the intermolecular correlations of ca. 5.5 and 10 Å are significantly different from each other, unlike that of ca. 15 Å. MD simulations were also performed. It turns out that the methyl substitution at the C2 position of imidazolium causes variation of the orientation of the nearest neighboring ion–ion interactions without significant changes in the long-range ordering, probably longer than 15 Å, of the ionic liquids.

Ion–ion interaction in room temperature ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate studied by large angle X-ray scattering experiment and molecular dynamics simulations

Large angle X-ray scattering (LAXS) experiment for 1-ethyl-3-methylimidazolium tetrafluoroborate [EMI +][BF 4 −] ionic liquid was carried out at 298 K, to reveal the closest ion–ion interaction in the ionic liquid. The intra-molecular atom–atom correlations based on the molecular geometries in crystals were subtracted from the total pair correlation function to yield the inter-molecular pair correlation function. In the inter-molecular pair correlation function, peaks of 3.4, 4.4 and 5.5 Å were successfully extracted as the closest ion–ion interactions. Molecular dynamics simulations based on the effective pair potentials were also performed to ascribe the peaks found in the experimentally evaluated inter-molecular pair correlation function at an atomistic level. The X-ray interference function derived from MD simulations and thus Fourier transferred X-ray weighted pair correlation function were reasonably agreement with those obtained by the experiment, the extracted peaks in the experimental inter-molecular pair correlation function can be appropriately attributed to the C (EMI +) - F (BF 4 −) atom–atom correlations. In addition, artificial MD simulations employed rigid models for the nonplanar and the planar EMI + isomers were performed to obtain further insight into the effect of the conformational isomerism on the ion–ion interactions in the ionic liquid. It turned out that the ion–ion interaction, namely the anion orientation around the cation, depends on the conformational isomerism of the cation from the artificial MD simulations.

Micro-solvent Cluster Extraction Using Aqueous Mixed Solvents of Ionic Liquid

Organic compounds (2-naphthol, phenol, 4-chlorophenol, 4-nitrophenol, and 1,3,5-naphthalenetrisulfonic acid) were sufficiently separated from mixtures during flow in a fused silica capillary tube (50 microm in i.d. and 45 cm in length) with an aqueous mixed solvent of an ionic liquid, 1-butyl-3-methylimidazolium chloride (BMIM(+)Cl(-)), without a specific separation column. The method is based on micro-solvent cluster formation in aqueous mixed solvents of ionic liquid and preferential solvation of solvent clusters to analytes. The measurement of large angle X-ray scattering (LAXS) of aqueous mixed solvents with an ionic liquid of tetrafluoroborate (BMIM(+)BF(4)(-)) indicated the formation of micro-solvent clusters of water and ionic liquid in the mixed solvent. A neutral polymer (polyvinylpyrrolidone, PVP) enhanced the separation. Polarized or ionic molecules eluted slowly. The theoretical plate numbers were 6320, 22907, 63645, and 37184 for 2-naphthol, phenol, 4-chlorophenol, and 4-nitrophenol, respectively, under the conditions of 1.0 M of BMIM(+)Cl(-) and 0.1 M of PVP; the flow rate was 1 microL min(-1). The separation mechanism is discussed from the viewpoint of the partition of analytes between micro-solvent clusters of water and organic solvent molecules.

Thermal Properties and Mixing State of Diol−Water Mixtures Studied by Calorimetry, Large-Angle X-Ray Scattering, and NMR Relaxation

Differential scanning calorimetry (DSC) has been performed on aqueous mixtures of three diols, which involve a linear carbon chain, HO-(CH 2) n -OH ( n = 3, 4, and 5), over the whole mole fraction range of diols. The DSC results have shown the alkyl chain parity for the freezing process of the aqueous mixtures: aqueous mixtures of 1,3-propanediol (PrD) and 1,5-pentanediol (PeD) are kept in the supercooled state or vitrified over a wide mole fraction range, while those of 1,4-butanediol (BuD) are easily crystallized. The structure of PrD-water mixtures has been elucidated by using the large-angle X-ray scattering (LAXS) technique. It has been suggested that the structural change of PrD-water mixtures occurs at PrD mole fractions of x PrD = 0.4 and 0.8: in the range of x PrD < or = 0.4 where the tetrahedral-like structure of water predominates, in the range of 0.4 < x PrD < 0.8 where both PrD and water structures coexist, and in the range of x PrD > or = 0.8 where the inherent structure of PrD is mainly formed. (17)O and (1)H NMR relaxation measurements have been made on aqueous mixtures of ethylene glycol (EG, n = 2), PrD, and BuD to clarify the dynamics of H 2 (17)O and diol molecules. The (17)O NMR relaxation rates have suggested that the rotational motion of water molecules is gradually retarded in the diol-water mixtures with increasing diol content and that the restriction of the motion is more remarkable in the order of EG < PrD < BuD. On the basis of all the results, together with comparison with those of methanol-water, ethanol-water, and 1-propanol-water mixtures previously reported, the mixing state of diol-water mixtures has been discussed at the molecular level.

An EXAFS Spectroscopic, Large‐Angle X‐Ray Scattering, and Crystallographic Study of Hexahydrated, Dimethyl Sulfoxide and Pyridine 1‐Oxide Hexasolvated Mercury(II) Ions

The structure of the solvated mercury(II) ion in water and dimethyl sulfoxide has been studied by means of large-angle X-ray scattering (LAXS) and extended X-ray absorption fine structure (EXAFS) techniques. The distribution of the Hg-O distances is unusually wide and asymmetric in both solvents. In aqueous solution, hexahydrated [Hg(OH(2))(6)](2+) ions in a distorted octahedral configuration, with the centroid of the Hg-O distance at 2.38(1) A, are surrounded by a diffuse second hydration sphere with HgO(II) distances of 4.20(2) A. In dimethyl sulfoxide, the six Hg-O and HgS distances of the hexasolvated [Hg{OS(CH(3))(2)}(6)](2+) complex are centered around 2.38(1) and 3.45(2) A, respectively. The crystal structure of hexakis(pyridine 1-oxide)mercury(II) perchlorate has been redetermined. The space group R(-)3 implies six equal Hg-O distances of 2.3416(7) A for the [Hg(ONC(5)H(5))(6)](2+) complex at 100 K. However, EXAFS studies of this compound, and of the solids hexaaquamercury(II) perchlorate and hexakis(dimethyl sulfoxide)mercury(II) trifluoromethanesulfonate, also with six equidistant Hg-O bonds according to crystallographic results, reveal in all cases strongly asymmetric Hg-O distance distributions. Vibronic coupling of valence states in a so-called pseudo-Jahn-Teller effect probably induces the distorted configurations.