Investigation of the Cholesteryl Oleate Mesophases by X-Ray Diffraction

The following phase transitions occurring in the cholesteryl oleate were investigated by X-ray diffraction: solid-isotropic liquid, isotropic liquid-cholesteric, cholesteric-smectic.

The sample purity was 98%. Strong pretransitional effects were observed at the solid-isotropic liquid phase transition and at the cholesteric-smectic phase transition.

At this last transition the longitudinal coherence length ξ_∥ appears to diverge as the critical temperature is approached in the cholesteric phase, whereas the transversal coherence length ξ_τ increases at the critical temperature in the smectic phase in an abrupt way. It seems from the temperature dependence analysis of the angular position of the low angle peak that the smectic phase is a smectic A phase and that a progressive melting of chains occurs at the temperature increases.     

X-Ray Diffraction by Liquid Crystals

Following a very brief historical review, x-ray diffraction by nematic and smectic liquid crystals is critically examined in terms of the data available and the structural models and molecular theories that have been proposed to explain it. Studiesof TBBA are used to illustrate some of the principal mesophases that have been distinguished. Other types of liquid crystals and their phase transitions are also briefly reviewed.

This analysis shows that careful experimental work is still needed to decide the kinds of models that best describe the various types of mesophases that have been shown to exist.     

Methods of Coherent X-Ray Diffraction Imaging

Crystallography Reports - Methods of coherent X-ray diffraction imaging of the spatial structure of noncrystalline objects and nanocrystals (nanostructures) are considered. Particular attention is...     

Simultaneous X-Ray Diffraction and Differential Scanning Calorimetry (XDDSC) in Studies of Molecular and Liquid Crystals

The technique of simultaneous X-ray diffraction and differential scanning calorimetry (XDDSC) is introduced into the field of molecular and liquid crystals. The technique allows fast time-resolved X-ray diffractograms to be recorded simultaneously with the recording of heat flow into or out of the specimen during a heating, cooling or isothermal scan. Structural transformations, as revealed by changes in the diffraction pattern, can thereby be unambiguously correlated with thermal events such as endo-or exo-therms or changes in heat capacity. Small and wide angle diffraction can be monitored. Sample pans and cuvettes made of boron nitride or graphite are used, both materials combining high transparency for X-rays with good thermal conductivity. Selected examples of application of the technique are presented.     

X-Ray Diffraction Studies of Liquid Crystalline Polymers

Thermotropic liquid crystalline copolyesters display an ordered fluid phase at elevated temperatures which permits the development of unusually high orientation at ambient temperatures. The transition which occurs upon cooling the high temperature nematic liquid crystalline phase very rapidly (e.g. fiber spinning) results in a polymeric glass with nematic structural order. Annealing increases structural order from the nematic glass toward ideal three dimensional crystalline order. Precision X-ray diffractometry has been used to directly observe changes in structural correlations which occur with annealing. Structural transitions range in character in these copolyesters from no change upon annealing to a transition from fully two dimensional to fully three dimensional structural order. Increased three dimensional order also results in substantially increased first order character of the high temperature phase transition. The chemical structure of co-monomers determines, in part, the final degree of dimensionality.     

Optimization of the Growth Technology for Crystals with Garnet Structure Based on X-Ray Diffraction Data

High efficiency of the methods of double-crystal X-ray diffractometry (DCXRD) and topography for improving the growth technology of highly homogeneous crystals has been demonstrated on the example of gadolinium gallium garnet (GGG) single crystals. The main types of structural defects observed in Czochralski-grown GGG crystals are found to be macroscopic inhomogeneity of composition distribution, caused by the facet effect manifestation; microinhomogeneous distribution of impurity and main components of the composition in striations; dislocations; and second-phase inclusions. The relationship between the type and density of newly formed defects and the technological conditions for crystal growth are considered. Optimization of the composition of crystals and their growth technology made it possible to obtain high-quality dislocation-free crystals of GGG and complex-substituted garnets on its basis for magneto-optical and microwave devices, elements of solid-state lasers, and other applications.     

Synthesis and X-Ray Crystal Structure of 1- and 2-Cinnamoyaloxy Acetonaphthones

Abstract  

The synthesis of titled compounds were achieved in one step using hydroxyl naphthones and substituted cinnamic acids in the presence of a catalytic amount of phosphorus oxychloride. X-ray crystal studies were undertaken for three compounds and the results are presented. Compounds 1 (C₂₂H₁₅F₃O₃) and 3 (C₂₁H₁₅BrO₃) formed a monoclinic crystals while compound 2 (C₂₂H₁₅F₃O₃) formed a triclinic crystals. The observed space group of these compounds is P2₁/c and P[`1] \bar{1} respectively. The 2-substituted compounds showed identical space group and showed a perpendicular arrangements of each of the substituents to the plane of the naphthyl ring. On the contrary, the 1-substituted cinnamoyal compound showed an orthogonal arrangement to naphthyl ring but the acetyl group was almost planar relative to the naphthyl moiety. The characterization of the structures of the compounds was also accomplished using high-resolution NMR spectroscopic techniques.     

X-Ray Diffraction and Physical Properties of Potassium Fullerides KxC70

Abstract

X-ray diffraction and magnetic-susceptibility measurements have been carried out for single phase K_xC₇₀ (x=1, 3, 4, 6 and 9) compounds synthesized by heating stoichiometric amount of K₉C₇₀ and C₇₀. The x-ray diffraction profiles show no structural transition down to 10K. The fairly large temperature-independent paramagnetic contribution was observed in x=3 and 4. The electrical resistivity has been measured for K evaporated C₇₀ film with increasing K thickness. Two resistivity minima were observed at x=1 and 4.     

X-ray Diffraction and DFT Studies of 2-Methoxy-5-phenylaniline

Abstract 2-Methoxy-5-phenylaniline, a promissor monomer for PANI studies, has been characterized by single-crystal X-ray diffraction at two temperatures: orthorhombic, space group P2₁2₁2₁, Z = 12 with a = 5.9900(2) ?, b = 20.4873(6) ?, c = 26.3727(8) ? and R = 0.0868 for 293(2) K and a = 5.8337(9) ?, b = 20.4428(31) ?, c = 26.0773(40) ? and R = 0.0669 for 120(2) K. There are three independent molecules in the unit cell. One of them is approximately planar, the other two have the phenyl rings rotated. At room temperature the two latter molecules are joined in dimers through H-bonds and at low temperature the same molecules are joined in columns that run along the a-axis. Index Abstract X-ray Diffraction and DFT Studies of 2-Methoxy-5-phenylaniline Ana T. Marques, Joana A. Silva, Manuela Ramos Silva, Ana Matos Beja, Licinia L. G. Justino, Abilio J. F. N. Sobral 2-Methoxy-5-phenylaniline, a promissor monomer for PANI studies, has been characterized by single-crystal X-ray diffraction at 293(2) K and 120(2) K. The three independent molecules in the unit cell show different conformations and establish distinct intermolecular H-bonds.      

Erratum to:Methods of Coherent X-Ray Diffraction Imaging

Crystallography Reports - An Erratum to this paper has been published: https://doi.org/10.1134/S106377452134006X     

Raman Scattering and X-Ray Diffraction Studies on Alkali-Metal Intercalated Clays

Abstract

Vermiculite and fluor-tetrasilicic mica were intercalated with alkali metals (Na, K and Rb) by vapor transport. X-ray and Raman scattering experiments were conducted to study the structure and lattice dynamics of the new clay compounds. When Rb and K atoms were intercalated to the host materials, superlattices were formed. In Na intercalated compounds, however, no superlattice x-ray diffraction peaks were found. Raman spectra exhibited drastic changes after alkali-metal intercalation, reflecting the structural changes found by our x-ray diffraction.     

X-Ray Diffraction Studies on Molecular Semiconductors Based on Charge-Transfer Complexes of Substituted Phenothiazines with 2,3-Dichloro-5,6-dicyano-p-benzoquinone

X-ray powder diffraction data on the molecular semiconductors based on the 1:1 charge-transfer complexes of the electron donors, viz. phenothiazine (PTZ), 2-chlorophenothiazine (CPZ), 2-acetyl phenothiazine (APZ) and 2-(trifluoromethyl)-phenothiazine (TPZ) with 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) have been reported in this paper. The indexing has been done by Ito's method. All the complexes have been found to have orthorhombic crystal structures. The lattice parameters for the individual complexes are as follows: (i) PTZ-DDQ: a = 6.020 Å, b = 9.775 Å, c = 24.280 Å; (ii) CPZ-DDQ: a = 5.830 Å, b = 8.070 Å, c = 20.280 Å; (iii) APZ-DDQ: a = 5.055 Å, b = 7.955 Å, c = 19.520 Å; (iv) TPZ-DDQ: a = 5.130 Å, b = 8.195 Å, c = 19.850 Å.     

X-Ray Diffraction Interferometer with One Slit: Computer Simulations and Analytics

Crystallography Reports - A theoretical basis and a method of accurate computer simulations for studying the properties of X-ray diffraction interferometer with one slit are formulated. The slit...     

Ray Theories in X-Ray Diffraction and Memories on the Borrmann Effect

The ray theories in ordinary optics are reviewed based on the Poynting vector and the wave packet for electromagnetic waves. They are extended to the two-beam (waves) cases in X-ray diffraction, because the rays are closely related to the Borrmann effect. It is pointed out that the approach of the wave packet is more fundamental than that of the Poynting vector. Some personal reminiscences of the Borrmann effect and of Borrmann himself are described.     

Synthesis and Molecular Structure of Sulfur Containing Cobalt Compounds

Abstract  

The reaction of cobalt (II) chloride hexahydrate and N-tert-butyl-2-thioimidazole (tm^t-Bu) yielded products [k²-(tm^t-Bu)₂]CoCl₂ (1) and [(tm^t-Bu)₂Co₂(μ-tm^t-Bu)₂Cl₂]·CH₃CN (2) at different reaction time. The single crystal X-ray diffraction analysis was carried out for 1 and 2 {Bruker Kappa Apex-II CCD diffractometer, MoK_α radiation}. Crystal data for 1: orthorhombic P212121 unit cell a = 8.195(6) ?, b = 13.778(10) ?, c = 17.354(11) ? and V = 1960(2) ?³ whereas the compound 2 crystallizes in monoclinic system P21/c with unit cell a = 10.069(7) ?, b = 11.181(7) ?, c = 18.156 ?, β = 95.322(4)° and V = 2035.4(2) ?³. The complex 1 contains one dimensional chain running along the a-axis and the complex 2 contains one dimensional chain running along the b-axis due to existence of different types of intermolecular interaction. The change in structure of the product is directly related to the reaction time i.e. reaction for lesser time produces mononuclear product and for longer time produces binuclear compound.     

Insights into Biaxial Ordering of Bent-Core Nematics: X-Ray Diffraction Evidence

Recently we have reported the first X-ray diffraction evidence of biaxial order in the fluid cybotactic nematic phase of a pair of trimethylated bent-core mesogens. This evidence is based on the splitting of the wide-angle diffuse scattering in the plane normal to the nematic director. The additional experimental data presented here provide further insights into this unprecedented behavior observed over the entire nematic phase. Although we could not determine the spatial extent of biaxial order—intracluster or intercluster—our observations reveal an enhanced biaxial orientational correlation in the transverse molecular packing, possibly reflecting stronger anisotropic interactions between nearest-neighbor mesogens.     

Crystallization and Preliminary X-Ray Diffraction Study of the C-Terminal Fragment of Myomesin-2

Crystallography Reports - The recombinant С-terminal fragment of myomesin-2 was purified to a homogeneous state. The crystallization conditions for the С-terminal fragment of myomesin-2...     

Cubic and Tetragonal Modifications in BaTiO3 Ceramic Samples: X-Ray Diffraction Analysis by the Rietveld Method

Crystallography Reports - The structures of ground ceramic BaTiO3 samples, prepared by solid-phase synthesis at maximum sintering temperatures of 1350, 1400, 1410, and 1500°C, have been...