X-Ray Diffraction Study of Aluminum Monoxycarbide

The structural characteristics of aluminum monoxycarbide Al₂OC are refined and systematized. Based on our X-ray diffraction data, three modifications of Al₂OC: -Al₂OC, '-Al₂OC, and '-Al₂OC have been revealed. Structural models are suggested for them.     

X-Ray Diffraction Study of Piperidine Octamolybdate

Piperidine octamolybdate [C₅H₅NH₂]₄[Mo₈O₂₆]·4H₂O (I) has been synthesized and characterized by X-ray diffraction analysis. Crystals I are monoclinic, space group P2₁/n, a=12.892(3), b=9.283(2), c=19.184(4) , =92.50(3)°, V=2293.7(9) ³, Z=2,_calc = 2.317 g/cm³.     

Rubidium Tetrachlorocadmate: X-Ray Diffraction Measurements and an Electronic Structure Study

The structure of Rb₂CdCl₄single crystal at room temperature has been determined from X-ray diffraction of the MoKαline (λ=0.7107 Å). After refinement through blocked least-squares methods, the reliability factorRin the final cycle is 3.07%. The following results have been obtained: tetragonal system, space groupI4/mmm,a=b=5.195(1) Å,c=16.130(1) Å;F(000)=380;Dm=3.243 g/cm³;Z=2. The structure can be viewed as made of layers of CdCl₆octahedra chains (Cd–Cl(1)=2.597(1) Å and Cd–Cl(2)=2.572(1) Å) separated by double slabs of rubidium atoms perpendicular to thecdirection. First-principles density functional theory calculations have been carried out to determine the electronic density distribution. The calculated equilibrium structure is in satisfactory agreement with the experimental data. Electronic density maps have been drawn from ab initio wavefunctions calculated both at the experimental and theoretical equilibrium geometries. Analysis of the calculated atomic populations confirms the highly ionic character of the electronic charge distribution in the crystal.     

Synthesis and X-Ray Diffraction Study of 2-(2-Acyl-1-phenylethenyl)pyrroles

Pyrroles add to 2-acyl-1-phenylacetylenes on the surface of silicon dioxide at 20-90°C affording structurally stable Z-isomers of 2-(2-acyl-1-phenylethenyl)pyrroles containing a strong intramolecular hydrogen bond. The geometry of these molecules was established by X-ray diffraction analysis of a single crystal of 2-(2-benzoyl-1-phenylethenyl)-4,5,6,7-tetrahydroindole.     

Synthesis, Characterization, and X-Ray Diffraction Analysis of Triethylenetetraammonium Tetrathiomolybdate

The reaction of gaseous H₂S with aqueous ammonium heptamolybdate in the presence of triethylenetetramine (trien) gave a red complex. The complex was recrystallized in hot water and characterized by element analysis and UV, visible, IR, and ¹H NMR spectroscopy. PMR has revealed accidental magnetic equivalence, resulting from the proximity of [MoS₄]^2- species in one complex molecule to the open triethylenetetramine ligand of another molecule. (TrienH₂)[MoS₄] crystallizes in the orthorhombic crystal system, space group Pca2₁, a=13.045(2), b=16.461(3), c=13.754(2) , =90, =90, =90°, V=2953.5(9) ³, Z=8, R₁=0.0323, wR₂=0.0730. The structure consists of the tetrahedral tetrathiomolybdate anions, forming an extended 3D framework in solids due to the interactions with triene cations via Mo-S...H-N hydrogen bonds.     

X-Ray Diffraction Study of Some Liquid Naphthalene Derivatives

Abstract

The structure of the liquids 1-Methylnaphthalene C₁₀H₇—CH₃ and 1-Chloronaphthalene C₁₀H₇—Cl was investigated using X-ray diffraction at 293 K. Monochromatic radiation MoK_α (λ = 0.7107Å) enabled determination of the scattered radiation inteasity between S₀ = 4pi sin υ₀/λ = 0.430 Å^?1 and S _max = 14.311 Å-1. Angular distributions of X-ray scattered intensity were measured, and differential radial distribution functions of electron density (DRDFs) were calculated. The mean distances between the neighbouring molecules and the ranges of the spheres of intermolecular ordering were found. X-ray structural analysis was applied for determination of the packing coefficient of molecules of the liquids studied. A simple model of short-range arrangement of the molecules was proposed, which seems to be valid for other weakly polar monosubstituted naphthalene derivatives in the liquid phase.     

Structure of Liquids. VIII. An X-Ray Diffraction Study of Liquid Mercury-Gallium Systems

Abstract

X-ray diffraction measurements were made at 0°, 30°, and 50°C on pure mercury and on two mercury-gallium systems of composition 0.9658 and 0.0197 mole fraction of mercury. Peak positions of the radial distribution functions for all samples show no significant change with temperature; the average position of the first and second peaks of the mercury curves are 3.01 Å and 5.80 Å, respectively. Coordination numbers for mercury as determined by the symmetrical curve method are 7.5, 7.3, and 7.0 atoms for 0°, 30°, and 50°C. The scattering function and the features of the structure obtained for the Ga-in-Hg solution are not significantly different from those of pure mercury; for the Hg-in-Ga solution, however, the coordination numbers are smaller than those for pure gallium, and the scattering functions are significantly different.     

NMR and X-Ray Diffraction Study of Some Inositol Derivatives 1

Abstract

We have determined the preferred conformers in solution by a detailed NMR analysis using COSY and HETCOR experiments of three inositol isomers: myo (1), scyllo (2) and epi (3) plus sixteen derivatives of myo-inositol: 1,2,3,4,5,6-hexa-O-acetyl-myo-inositol (4), 1,2,-O-isopropylidene-myo-inositol (5), 1,2:4,5-di-O-isopropylidene-myo-inositol (6), 3,4,5,6-tetra-O-acetyl-1,2-O-isopropylidene-myo-inositol (7), 3,4,5,6-tetra-O-acetyl-myo-inositol (8), 1,2-O-isopropylidene-3,6-di-O-tosyl-myo-inositol (9), 1,2-O-isopropylidene-3,4,6-tri-O-tosyl-myo-inositol (10), 1,2:4,5-di-O-isopropylidene-3-O-tosyl-myo-inositol (11), 3,6-di-O-benzyl, 1,2:4,5-di-O-isopropylidene-myo-inositol (12), 3,6-di-O-benzyl-1,2-O-isopropylidene-myo-inositol (13), 3,6-di-O-benzyl-myo-inositol (14), 1,2-O-cyclohexylidene-myo-inositol (15), 1,2:4,5-di-O-cyclohexylidene-myo-inositol (16), 1,2:5,6-di-O-cyclohexylidene-myo-inositol (17), 1,3,5-O-(orthoformate)-myo-inositol (18) and 2-benzyl-1,3,5-O-(orthoformate)-myo-inositol (19). The X-ray diffraction structure of compounds 2, 6-8, 18 and 19 are reported.

     

X-Ray Diffraction Study of Micro Amounts of Polycrystalline Samples

With the use of reference polycrystalline 6h-Al₂O₃ (NIST SRM- 1976) and MoO₃ samples we consider the most significant geometric and physical factors affecting the accuracy of X-ray diffraction data obtained on a diffractometer equipped with a flat two-dimensional detector (Debye-Scherrer scheme). A general strategy to measure polycrystalline samples in the amount of 20–30 fug is proposed. By the example of SRM-1976 it is shown that with the proper processing of two-dimensional diffraction patterns and the introduction of certain corrections the angles 2θ can be measured with the accuracy not less than ±0.01°. Even with a strong tendency of particles towards preferred orientation the relative intensities of diffraction reflections are shown to be obtained with the accuracy not less than ±10%.     

X-Ray Diffraction Study of 2-Aminopropenenitrile at 97 K

2-Aminopropenenitrile crystallizes in the space group P2₁2₁2₁ with two molecules in the asymmetric unit. Both molecules show appreciable pyramidalization at the amino group. The crystal structure is built from approximately centrosymmetric dimers stabilized by hydrogen bonding between the amino group of each molecule and the nitrile group of its partner. The dimers are linked into chains by further hydrogen bonds in which the amino group of one molecule acts as donor, the amino group of the other as acceptor. The two types of molecule thus play different roles in the crystal structure. Electron density difference maps for the two independent molecules show characteristic bonding density features. The molecular structure as obtained by the low-temperature X-ray analysis is closely similar to that derived from ab initio molecular orbital calculations and leads to rotational constants close to those obtained from a microwave spectroscopic study.     

时间分辨原位同步X射线衍射技术在分子筛研究中的应用

介绍了时间分辨原位同步X射线衍射技术(in situ TR XRSD)的原理。该技术以其原位测量性和时间分辨性为特征,广泛应用于分子筛研究的各个领域。举例阐述了该技术在水热合成条件的优化、结晶动力学参数测定、成核机理探索、转晶过程和机理、晶体参数变化的监测和骨架外阳离子迁移等过程研究中的应用原理和方法。     

高温下X射线衍射法对铁氧化过程的研究

在500℃和800℃条件下,采用高温X射线衍射法对铁粉的氧化过程进行研究.结果表明,随着温度升高,铁及其氧化物的晶面间距均有所增加,而温度恒定时晶面间距没有变化,温度是影响晶格变化的主要因素.温度升高,晶面间距加大,为铁离子在氧层中的迁移提供了通道,有利于氧化过程的进行.     

X-Ray Diffraction Study of Fine Iron Powder Modified with Cross-Linked Dextran

The structure of fine iron powders modified with cross-linked dextran was studied by X-ray diffraction analysis. The parameters of short-range ordering of dextran in the modifying coating were determined as influenced by dextran content. The parameters for quantitative phase analysis was proposed.     

面粉中滑石粉的X射线衍射分析

通过四氯化碳分离或高温灰化,X射线衍射分析测定面粉中掺入的滑石粉。其中灰化处理适宜温度为500~750℃。该方法简便、快速,灵敏度高,样品用量少,准确可靠,可推广为检测面粉质量的一种较理想的手段。     

Short-Range Ordering in Liquid Bicyclohexyl by X-Ray Diffraction

Abstract

The paper reports results of the X-ray diffraction structural studies of liquid bicyclohexyl, C₆H₁₁—C₆H₁₁ at room temperature, using CuK _α radiation. Angular distribution of X-ray scattered intensity was measured, and the electron-density radial-distribution function was calculated. Computer techniques were used to minimize the effects of experimental errors, uncertainties in the scattering factors, and termination errors. Good agreement between the theoretical and experimental functions was obtained on assuming the statistically most probable model of this molecule. The structural data obtainable by X-ray analysis for liquid bicyclohexyl were discussed. The mean distances between the neighbouring molecules and the radii of coordination spheres were found. The maxima in the differential radial distribution function were at: r ₁ = 4.68, r ₂ = 5.57, r ₃ = 6.62, r ₄ = 8.05 Å. X-ray structural analysis was applied to determine the packing coefficient of bicyclohexyl molecules. A simple model of short-range arrangement of the molecules in liquid bicyclohexyl was proposed.     

A New Silicate Clathrate Hydrate: An X-Ray Diffraction and Nuclear Magnetic Resonance Study of a System with Octameric Silicate Anions and Trivalent Cations

The first crystal structure is reported for a silicate clathrate hydrate involving a triply charged cation [C₁₈H₃₀N₃]³⁺ and an octameric cubic silicate cage. The structure is essentially a host/guest system, with the silicate cages linked into a framework by hydrogen bonding to water molecules. The space group is P with Z = 2, and the asymmetric unit includes a complete cation and half the anion, plus 21 water molecules (4 of which are in disordered positions). Solid-state (CPMAS) ²⁹Si and ¹³CNMR spectra are consistent with the diffraction-determined structure and indicate substantial distortion of the anion from cubic symmetry. Solution-state spectra of precursor solutions and of melted material are also presented and discussed.     

ChemInform Abstract: Thermal Effect on BaFCl: High-Temperature X-Ray Diffraction.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Resonant X-Ray Diffraction: Forbidden Bragg Reflections Induced by Atomic Displacements

The displacements of atoms from their equilibrium sites with high symmetry are accompanied by the appearance of the additional components of the resonant susceptibility tensor and become a source of additional anisotropy of resonant X-ray scattering. As a result, forbidden Bragg reflections can appear near absorption edges, which are absent far from the edges in a regular crystal. These reflections can be induced by dynamic thermal atomic vibrations or by static displacements because of modulation and point defects. A theoretical approach is suggested that allows the calculation of the susceptibility tensor and a set of forbidden reflections, in the case of small atomic displacements. This approach is based on the calculation of the displacements using the mechanic representation of space groups. The example of a space group Pnma with resonant atoms in 4(c) position is discussed in detail.     

锌镀层织构的X-射线衍射研究

采用X-射线衍射法研究了在控制电位或电流沉积得到的锌镀层的织构.结果表明,锌镀层的晶面取向强烈地依赖于极化电位及沉积时间.根据几何选择理论和向外生长模式,以及结晶学、电化学因素讨论了所得的结果.