Liquid structure of acetic acid-water and trifluoroacetic acid-water mixtures studied by large-angle X-ray scattering and NMR

The structures of acetic acid (AA), trifluoroacetic acid (TFA), and their aqueous mixtures over the entire range of acid mole fraction xA have been investigated by using large-angle X-ray scattering (LAXS) and NMR techniques. The results from the LAXS experiments have shown that acetic acid molecules mainly form a chain structure via hydrogen bonding in the pure liquid. In acetic acid-water mixtures hydrogen bonds of acetic acid-water and water-water gradually increase with decreasing xA, while the chain structure of acetic acid molecules is moderately ruptured. Hydrogen bonds among water molecules are remarkably formed in acetic acid-water mixtures at xA相似文献   

Effect of zeolite matrix structure on the stabilization of silver clusters

Silver clusters characterized by an absorption band at 320–340 nm are found to be easily stabilized by zeolites of mordenite type. Size of the clusters is discussed on the basis of results on introducing silver clusters into the zeolites with various channel diameters and on electron microscopy and low-angle X-ray scattering (LAXS) data.     

Structure and dynamics of sulfate ion in aqueous solution--an ab initio QMCF MD simulation and large angle X-ray scattering study

The hydrated sulfate ion has been characterized in aqueous solution in structural and dynamic aspects using ab initio quantum mechanical charge field (QMCF) molecular dynamics (MD) simulation and large angle X-ray scattering (LAXS) methods. The LAXS data show an average coordination number of the sulfate ion of up to 12 water molecules bound through hydrogen bonding, while the QMCF MD simulation displays a wide range of coordination numbers between 8 and 14 with an average value of approximately 11. The Os...Ow distance cannot be distinguished from the Ow...Ow distance in the LAXS experiment; the weighted mean O...O distance is 2.880(10) A. In the simulation, the Os...Ow and Ow...Ow distances are found to be very similar, namely, 2.86 and 2.84 A, respectively. The S-Os bond and S...Ow distance have been determined by the LAXS experiment as 1.495(6) and 3.61(2) A, respectively, indicating an average nearly tetrahedral S-Os...Ow angle. The approximately 5% deviations of simulation distances (1.47 and 3.82 A) from the experimental ones can probably be ascribed to the neglect of correlation energy in the quantum mechanical method. The mean residence time of water ligands at O atoms, 2.57 ps, is longer than that in pure water, 1.7 ps, characterizing the sulfate ion as a weak structure maker.     

Formation of a heteronuclear hydrolysis complex in the Th(IV)-Fe(III) system

The speciation in the mixed Th(IV)-Fe(III) system has been studied in aqueous solution in the pH range of 2.0-4.8. In the individual systems iron(III) and thorium(IV) hydrolyze easily and hydrolysis products precipitate at approximately pH ≥ 2.0 and 4.0, respectively, at the metal concentrations used in this study, 0.02-0.05 mol dm(-3). In the mixed Th(IV)-Fe(III) system precipitation of ferrihydrite takes place after months of storage at low pH values, 2.0 (six-line ferrihydrite) and 2.3 (two-line ferrihydrite), as identified by X-ray powder diffraction. In the pH range 2.9-4.5 no precipitation was observed after 24 months. Two thorium(IV)-iron(III) solutions with pH = 2.9, C(Th) = 0.02 and 0.05 mol dm(-3) and C(Fe) = 0.02 mol dm(-3), were studied by extended X-ray absorption fine structure, EXAFS, using the Fe K and Th L(3) edges, and a third solution with pH = 2.9 and C(Th) = C(Fe) = 0.40 mol dm(-3) by large angle X-ray scattering, LAXS, to determine the structure of the predominating species. A heteronuclear hydrolysis complex with the composition [Th(2)Fe(2)(μ(2)-OH)(8)(H(2)O)(12)](6+) is proposed to form in solution, with Th···Th, Th···Fe and Fe···Fe distances of 3.94(2) and 3.96(2), 3.41(3) and 3.43(2), 3.04(2) and 3.02(4) ?, as determined by EXAFS and LAXS, respectively.     

Hydration of the calcium ion. An EXAFS, large-angle x-ray scattering, and molecular dynamics simulation study.

The structure of the hydrated calcium(II) ion in aqueous solution has been studied by means of extended X-ray absorption fine structure spectroscopy (EXAFS), large-angle X-ray scattering (LAXS), and molecular dynamics (MD) methods. The EXAFS data displayed a broad and asymmetric distribution of the Ca-O bond distances with the centroid at 2.46(2) A. LAXS studies on four aqueous calcium halide solutions (1.5-2 mol dm(-)(3)) gave a mean Ca-O bond distance of 2.46(1) A. This is consistent with a hydration number of 8 determined from correlations between mean distances and coordination numbers from crystal structures. The LAXS studies showed a second coordination sphere with a mean Ca.O(II) distance of 4.58(5) A, and for the hydrated halide ions the distances Cl.O 3.25(1) A, Br.O 3.36(1) A, and I.O 3.61(1) A were obtained. Molecular dynamics simulations of CaCl(2)(aq) were performed using three different Ca(2+)-OH(2) pair potentials. The potential from the GROMOS program gave results in agreement with experiments, i.e., a coordination number of 8 and an average Ca-O distance of 2.46 A, and was used for further comparisons. Theoretical EXAFS oscillations were computed for individual MD snapshots and showed very large variations, though the simulated average spectrum from 2000 snapshots gave satisfactory agreement with the experimental EXAFS spectra. The effect of thermal motions of the coordinated atoms is inherent in the MD simulation method. Thermal disorder parameters evaluated from simulated spatial atom distribution functions of the oxygen atoms coordinated to the calcium ion were in close agreement with those from the current LAXS and EXAFS analyses. The combined results are consistent with a root-mean-square displacement from the mean Ca-O distance of 0.09(2) A in aqueous solution at 300 K.     

Structure of the hydrated and dimethyl sulfoxide solvated rubidium ions in solution

The structure of the hydrated and the dimethyl sulfoxide solvated rubidium ions in solution has been determined by means of large-angle X-ray scattering (LAXS) and extended X-ray absorption fine structure (EXAFS) studies. The models of the hydrated and dimethyl sulfoxide solvated rubidium ions fitting the experimental data best are square antiprisms with Rb-O bond distances of 2.98(2) and 2.98(3) A, respectively. The EXAFS data show a significant asymmetry in the Rb-O bond distance distribution with C(3) values of 0.0076 and 0.015 A(3), respectively. No second hydration sphere is observed around the hydrated rubidium ion. The dimethyl sulfoxide solvated rubidium ion displays a Rb-O-S bond angle of ca. 130 degrees, which is typical for a medium hard electron acceptor such as rubidium.     

Coordination chemistry of the solvated silver(I) ion in the oxygen donor solvents water, dimethyl sulfoxide, and N,N'-dimethylpropyleneurea

The hydrated and dimethyl sulfoxide and N,N'-dimethylpropyleneurea solvated silver(I) ions have been characterized structurally in solution by means of extended X-ray absorption fine structure (EXAFS) and large-angle X-ray scattering (LAXS). The coordination chemistry of the hydrated and dimethyl sulfoxide solvated silver(I) ions has been reevaluated because of different results from the EXAFS and LAXS methods reported previously. Consistent results are obtained with a linearly distorted tetrahedral model with two short and approximately two long Ag-O bond distances: mean Ag-O bond lengths of 2.32(1) and 2.54(1) A for the hydrate, 2.31(1) and 2.48(2) A for the dimethyl sulfoxide solvate, and 2.31(1) and 2.54(2) A for the N,N'-dimethylpropyleneurea solvate, in solution.     

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 ?. 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) ?, 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) ?, 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) ?. New and improved ionic radii for the lead(II) ion in 4-8-coordination in hemi and holodirected configurations are proposed using crystallographic data.     

Steric effects control the structure of the solvated lanthanum(III) ion in aqueous, dimethyl sulfoxide, and N,N'-dimethylpropyleneurea solution. An EXAFS and large-angle X-ray scattering study

The structure of the solvated lanthanum(III) ion has been determined in aqueous, dimethyl sulfoxide, and N,N'-dimethylpropyleneurea solution by means of the EXAFS and large-angle X-ray scattering (LAXS) techniques. The close agreement between the EXAFS spectra of solid nonaaqualanthanum(III) trifluoromethanesulfonate and of an aqueous lanthanum(III) perchlorate solution shows that the hydrated lanthanum(III) ion in aqueous solution most probably has the same structure as in the solid, i.e., nine water molecules coordinated in a tricapped trigonal prismatic configuration. The data analysis from EXAFS and LAXS measurements of the aqueous solution resulted in the La-O bond distances 2.52(2) and 2.65(3) A to the water molecules in the prism and the capping positions, respectively. The LAXS study shows a second hydration sphere consistent with approximately 18 water molecules at 4.63(2) A. The EXAFS spectra of solid octakis(dimethyl sulfoxide)lanthanum(III) trifluoromethanesulfonate and a dimethyl sulfoxide solution of this salt are also similar. The data analysis of EXAFS and LAXS measurements assuming eight-coordination around lanthanum yielded an La-O bond distance of 2.50(2) A, and an La...S distance of 3.70(3) A, giving an La-O-S angle of 133(2) degrees. The EXAFS data of an N,N'-dimethylpropyleneurea solution of lanthanum(III) trifluoromethanesulfonate gave the La-O bond distance 2.438(4) A and the La...C distance 3.41(2) A, which correspond to an La-O-C angle of 131(2) degrees. The La-O bond distance is consistent with seven-coordination around lanthanum, on the basis of the variation of the ionic radii of the lanthanum(III) ion with different coordination numbers.     

Experimental evidence for a variable first coordination shell of the cadmium(II) ion in aqueous, dimethyl sulfoxide, and N,N'-dimethylpropyleneurea solution

A combined extended X-ray absorption fine structure (EXAFS) and large angle X-ray scattering (LAXS) investigation has been performed to evaluate the coordination structure of the cadmium(II) ion in aqueous, dimethyl sulfoxide, and N,N'-dimethylpropyleneurea (dmpu) solutions. This approach has singled out the existence of a flexible coordination shell around the cadmium(II) ion in aqueous and dimethyl sulfoxide solutions, whereas a regular octahedral complex is detected in dmpu. The EXAFS and LAXS techniques provide different values of the Cd-O first shell distance (2.27(1) A and 2.302(5) A, respectively) for the hydrated and dimethyl sulfoxide solvated complexes, and this discrepancy is originated by the simultaneous presence of hexa- and heptacoordinated complexes in solution, giving rise to a broad distribution of distances around the ion. These findings demonstrate that, in solution, the cadmium(II) ion forms quite flexible hydration and dimethyl sulfoxide solvate complexes undergoing a solvent exchange with unusually stable seven-coordinated intermediate complexes, and therefore the mean ion-solvent distance is longer in solution than in the solid state. In the dmpu solution, due to the bulkiness of the solvent molecules, the octahedral cadmium(II) solvate is extremely crowded and it is not possible for a seventh ligand to enter the inner-coordination shell. This investigation shows that the combined analysis of the EXAFS and LAXS data allows a reliable determination of the structural properties of electrolyte solutions, also in the presence of flexible coordination shell with a variable number of coordinating molecules.     

Crystal structure of lead(II) acetylacetonate and the structure of the acetylacetone solvated lead(II) ion in solution studied by large-angle X-ray scattering

The crystal structure of bis(acetylacetonato)lead(II) and the structure of the acetylacetone solvated lead(II) ion in solution have been determined by single-crystal X-ray diffraction and large-angle X-ray scattering (LAXS), respectively. The acetylacetone is deprotonated and acts as a bidentate anionic ligand (acac-) in the solid Pb(acac)2 compound. The lead(II) ion binds four oxygen atoms strongly in a nearly flat pyramidal configuration with Pb-O bond lengths in the range 2.32-2.37 A, and additionally three oxygens from neighboring complexes at 3.01-3.26 A. Acetylacetone acts as a solvent (Hacac) at dissolution of lead(II) trifluoromethanesulfonate forming a pentasolvate with a mean Pb-O bond distance of 2.724(5) A. The 6s2 lone electron pair on the lead(II) ion becomes stereochemically active in the crystalline acetylacetonate complex, while it is inactive in the solvate in solution. The solution was also analysed using IR and 1H NMR spectroscopy.     

Thermal properties and mixing state of ethylene glycol-water binary solutions by calorimetry, large-angle X-ray scattering, and small-angle neutron scattering

Thermal properties and mixing states of ethylene glycol (EG)-water binary solutions in the entire mole fraction range of EG, 0 < or = x(EG) < or = 1, have been clarified by using differential scanning calorimetry (DSC), large-angle X-ray scattering (LAXS), and small-angle neutron scattering (SANS) techniques. The DSC curves obtained have shown that the EG-water solutions over the range of EG mole fraction 0.3 < or = x(EG) < or = 0.5 are kept in the supercooling state until approximately 100 K, and those in the range of 0.6 < or = x(EG) < or = 0.8 are vitrified, and those in the ranges of 0 < x(EG) < or = 0.2 and 0.9 < or = x(EG) < 1 are crystallized. The radial distribution function (RDF) for pure EG obtained from the LAXS measurements has suggested that a gauche conformation of an EG molecule is favorable in the liquid. The RDFs for the EG-water solutions have shown that the structure of the binary solutions moderately changes from the inherent structure of EG to the tetrahedral-like structure of water when the water content increases. The SANS intensities for deuterated ethylene glycol (HOCD2CD2OH) (EGd4)-water solutions at x(EG) = 0.4 and 0.6 have not been significantly observed in the temperature range from 298 to 173 K, showing that EG and water molecules are homogeneously mixed. On the other hand, the SANS intensities at x(EG) = 0.2 and 0.9 have been strengthened when the temperature decreases due to crystallization of the solutions. On the basis of all the present results, a relation between thermal properties of EG-water binary solutions and their mixing states clarified by the LAXS and SANS measurements has been discussed at the molecular level.     

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) ?, 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 ?, respectively, as well as for five- and six-coordinate sodium(I), 1.02 and 1.07 ?, respectively. The ionic radii for six- and seven-coordinate K(+), 1.38 and 1.46 ?, respectively, and eight-coordinate Rb(+) and Cs(+), 1.64 and 1.73 ?, 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.     

X-ray photoelectron spectra of complexes with 1-(D-3-mercapto-2-methylpropionyl)-L-proline and Ni(II), Cd(II) and Cu(I): synthesis and LAXS study of Cu(I) derivative

Metal complexes of general formula Na2M(CAP)2xH2O (with M = Cd(II) or Ni(II), x = 7 and 4, respectively, CAP = 1-(D-3-mercapto-2-methylpropionyl)-L-proline) and NaCuCAPx3H2O have been synthesized as amorphous compounds and studied by means of X-ray photoelectron spectroscopy (XPS). Cu(I) derivative has been studied by IR, XPS and large-angle X-ray scattering (LAXS). IR data and the chemical shift of core level signals suggest that CAP is bonded to the metal via the sulphur atom and the carbonylic oxygen. LAXS data confirm this finding and are consistent with a tetrahedral configuration around the copper ion. The CAP molecule is bonded through the sulphur and the carbonylic oxygen and two water molecules complete the coordination around the metal. The sodium ion exhibits a tetrahedral configuration and interacts with the carboxylic group and two water molecules. One of these is bridging bonded between copper and sodium. No metal-nitrogen bonds are present.     

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(+)...TFSI(-) interaction, the EMI(+)...EMI(+) and TFSI(-)...TFSI(-) interactions, and the second neighbor EMI+...TFSI(-) interaction, respectively. The ionic liquid involves two conformers, C(1) (cis) and C(2) (trans), for TFSI(-), and two conformers, planar cis and nonplanar staggered, for EMI(+), and thus the system involves four types of the EMI(+)...TFSI(-) interactions in the liquid state by taking into account the conformers. However, the EMI(+)...TFSI(-) interaction is not largely different for all combinations of the conformers. The same applies alsoto the EMI(+)...EMI(+) and TFSI(-)...TFSI(-) interactions. It is suggested from the 13C NMR that the imidazolium C(2) proton of EMI(+) strongly interacts with the O atom of the -SO(2)(CF(3)) group of TFSI(-). The interaction is not ascribed to hydrogen-bonding, according to the MD simulation. It is shown that the liquid structure is significantly different from the layered crystal structure that involves only the nonplanar staggered EMI(+) and C(1) TFSI(-) conformers.     

煤基和石油基C7-沥青质的结构特征及缔合行为

采用核磁(NMR)、小角散射分析(SAXS)、X射线光电子能谱(XPS)、改进的B-L法等手段,研究了煤基C7-沥青质(CT-asp)和石油基C7-沥青质(M-asp)两类沥青质的化学组成、官能团和分子结构等组成结构特征以及差异性,进而通过极性溶剂中沥青质稳定参数研究两类沥青质的缔合行为和聚集体尺寸以及两者之间的氢键和酸碱作用。结果表明,CT-asp分子芳香环数较少且有较多短烷基侧链,且芳香度较高,较高含量氧杂原子以芳香醚和酚羟基赋存形态为主;而M-asp的芳香核尺寸和平均相对分子质量明显高于CT-asp,芳香环数虽较多且有较多长烷基支链,且芳香度较小;两类沥青质缔合聚集程度关联物质的量比(n_(CT-asp)/n_(M-asp))及其分子结构特征,源于杂原子官能团的氢键和酸碱作用是两类沥青质缔合的主要作用力。     

Assessment and formation mechanism of laser-induced periodic surface structures on polymer spin-coated films in real and reciprocal space

In this work we evaluate the potential of grazing incidence X-ray scattering techniques in the investigation of laser-induced periodic surface structures (LIPSSs) in a series of strongly absorbing model spin-coated polymer films which are amorphous, such as poly(ethylene terephthalate), poly(trimethylene terephthalate), and poly(carbonate bisphenol A), and in a weaker absorbing polymer, such as semicrystalline poly(vinylidene fluoride), over a narrow range of fluences. Irradiation was performed with pulses of 6 ns at 266 nm, and LIPSSs with period lengths similar to the laser wavelength and parallel to the laser polarization direction are formed by devitrification of the film surface at temperatures above the characteristic glass transition temperature of the polymers. No crystallization of the surface is induced by laser irradiation, and crystallinity of the material prevents LIPSS formation. The structural information obtained by both atomic force microscopy and grazing incidence small-angle X-ray scattering (GISAXS) correlates satisfactorily. Comparison of experimental and simulated GISAXS patterns suggests that LIPSSs can be well described considering a quasi-one-dimensional paracrystalline lattice and that irradiation parameters have an influence on the order of such a lattice.     

The hydration of the scandium(III) ion in aqueous solution and crystalline hydrates studied by XAFS spectroscopy, large-angle X-ray scattering and crystallography

The structures of the hydrated scandium(III) ion and of the hydrated dimeric hydrolysis complex, [Sc2(mu-OH)2]4+, in acidic aqueous solutions have been characterized by X-ray absorption fine structure (XAFS) and large-angle X-ray scattering (LAXS) methods. Comparisons with crystalline reference compounds containing hydrated scandium(III) ions in well characterized six-, seven- and eight-coordinated polyhedra have been used to evaluate the coordination numbers and configurations in aqueous solution. In strongly acidic aqueous solution the structure of the hydrated scandium(III) ion is found to be similar to that of the eight-coordinated scandium(III) ion with distorted bicapped trigonal prismatic coordinating geometry in the crystalline [Sc(H2O)(8.0)](CF3SO3)3 compound. The EXAFS data reveal for the solution, as for the solid, a mean Sc-O bond distance of 2.17(1) Angstrom to six strongly bound prism water molecules, 2.32(4) Angstrom to one capping position, with possibly another capping position at about 2.5 Angstrom. The LAXS study supports this structural model and shows furthermore a second hydration sphere with approximately 12 water molecules at a mean Sc...O(II) distance of 4.27(3) Angstrom. In less acidic concentrated scandium(III) aqueous solutions, the dimeric hydrolysis product, [Sc2(mu-OH)2(H2O)10]4+, is the predominating species with seven-coordinated scandium(III) ions in a double hydroxo bridge and five terminal water molecules at a mean Sc-O bond distance of 2.145 Angstrom. Hexahydrated scandium(III) ions are found in the crystal structure of the double salt [Sc(H2O)6][Sc(CH3SO3)6], which crystallizes in the trigonal space group R3[combining macron] with Z = 6 and the unit cell dimensions a = 14.019(2) and c = 25.3805(5) Angstrom. The Sc-O distances in the two crystallographically unique, but nearly identical, [Sc(H2O)6]3+ entities (both with 3[combining macron] imposed crystallographic symmetry) are 2.085(6) and 2.086(5) Angstrom, while the mean Sc-O distance in the near octahedral [Sc(OSO2CH3)6]3- entities (with three-fold symmetry) is 2.078 Angstrom.     

Structure of methanol confined in MCM-41 investigated by large-angle X-ray scattering technique

Large-angle X-ray scattering (LAXS) measurements over a temperature range from 223 to 298 K have been made on methanol confined in mesoporous silica MCM-41 with two different pore diameters, 28 A (C14) and 21 A (C10), under both monolayer and capillary-condensed adsorption conditions. To compare the structure of methanol in the MCM-41 pores with that of bulk methanol, X-ray scattering intensities for bulk methanol in the same temperature range have also been measured. The radial distribution functions (RDFs) for the monolayer methanol samples showed that methanol molecules are strongly hydrogen bonded to the silanol groups on the MCM-41 surface, resulting in no significant change in the structure of adsorbed methanol with respect to the pore size and temperature. On the other hand, the RDFs for the capillary-condensed methanol samples showed that hydrogen-bonded chains of methanol molecules are formed in both pores. However, the distance and number of hydrogen bonds estimated from the RDFs suggested that hydrogen bonds between methanol molecules in the pores are significantly distorted or partly disrupted. It has been found that the hydrogen bonds are more distorted in the smaller pores of MCM-41. With decreasing temperature, however, the hydrogen-bonded chains of methanol in the pores were gradually ordered. A comparison of the present results on methanol in MCM-41 pores with those on water in the same pores revealed that the structural change with temperature is less significant for confined methanol than for confined water.     

Orientation of the α- and γ-modification of elastic polypropylene at uniaxial stretching

New metallocene catalysts applied to propylene polymerization expand the range of properties of polypropylene (PP), resulting in semi-crystalline materials having crystallinities below 60% up to X-ray amorphous highly elastic ones. To date the origin of the unique elastic mechanical behavior of such low crystalline PP is not completely understood. Therefore, the microscopic orientation of those PPs due to uniaxial stretching was investigated using wide-(WAXS) and small-angle X-ray scattering (SAXS). The aim of this study was to correlate these orientations or changes in the developed fiber textures with the macroscopic stress-strain behavior. This includes efforts to come closer to the main question of the nature of the physical cross-links in these not chemical cross-linked homopolymers, which is the reason for the high elastic behavior. Therefore, high molecular weight metallocene PPs showing different crystallinities (0-36%) were stretched to several elongations and the structural changes during the deformation were recorded by X-ray scattering. Stress-strain measurements show the great potential of these PPs as a thermoplastic rubber material. For quantitative analysis and discussion of the polymer chain orientations, the orientation functions were calculated. Correlations between the orientation functions and the stress-strain curves allow an interpretation of the macroscopic behavior on a microscopic scale. A higher cross-linking density in elongated samples indicates that the network, which is responsible for the elasticity, mainly built up by strain-induced morphology changes and chain orientations.