2,6-Diaziadamantane: a single-crystal X-ray diffraction study and theoretical calculations

The first single-crystal X-ray diffraction study of 2,6-diaziadamantane (2), a compound containing two diazirine functionalities, and B3LYP/6-311+G* and MP2/6-311+G* calculations relating to the interaction between carbon-nitrogen and nitrogen-nitrogen covalent bonds and electron density within the diazirine rings have been performed. In addition, the protonation of 2-aziadamantane (1) has been investigated. The single-crystal X-ray diffraction study of 2, including UV/vis titrations of 1, corroborate the theoretical conclusion that the low basicity can be attributed to a rehybridization of the nitrogen lone pairs. Moreover, the strain in diazirine is unusually small.     

Simultaneous measurements of X-ray diffraction–differential scanning calorimetry

Journal of Thermal Analysis and Calorimetry - Ganciclovir (GCV) is an antiviral drug for treating cytomegalovirus infections. This drug is reported to exist in four crystal forms in the solid...     

Azine bridged silver coordination polymers: Powder X-ray diffraction route to crystal structure determination of silver benzotriazole

In continuation of our interest in solid-state structures of silver complexes of photographic importance, the structure for silver benzotriazole (AgBZT), has now been obtained. The preferred method for solving crystal structures is via single-crystal X-ray diffraction (XRD). However, for some materials, growing single crystals of appropriate size and quality is often difficult or even impossible. AgBZT is an example of such a silver complex with poor solubility. The usual routes to preparing single crystals using recrystallization from a cooperating solvent resulted in polycrystalline powder samples. We propose a crystal structure for AgBZT, solved from synchrotron X-ray powder diffraction data, using a direct-space Monte Carlo simulated annealing approach. AgBZT crystals are monoclinic, (P2₁/c), with unit cell dimensions, a=14.8052(3) Å, b=3.7498(4) Å, c=12.3495(12) Å, and β=114.200(6)°. The AgBZT complex is constructed from all three of the Benzotriazole (BZT) nitrogens bonding to a separate silver atom. As a consequence of this bonding mode, the structure is a highly cross-linked, coordination polymer.     

Hydrogen bond in 3-acetyl-4-hydroxycoumarin: X-ray diffraction study and quantum-chemical calculations

The proton transfer and the character of the strong intramolecular O--H...O hydrogen bond (O...O 2.442 ) in 3-acetyl-4-hydroxycoumarin were analyzed based on the results of X-ray diffraction study in the temperature range from 100 to 353 K and quantum-chemical B3LYP/6-31G(d,p) calculations. The barrier to proton transfer along the H-bond line is low (2 kcal mol^–1). However, no proton transfer was observed in the crystal at 100 K. Bader's topological analysis of the electron density distribution both in the crystal and in the isolated molecule demonstrated that the hydrogen bond corresponds to an intermediate type of interatomic interactions (E(r) < 0, ²(r) > 0 at the critical point (3, –1)).     

Impedance measurements for pressed-pellet electrode membranes based on silver iodide and silver iodide/silver sulfide with solution contacts

Impedance characteristics of pressed pelletm membranes based on silver iodide, mixed $\text{AgI}\text{Ag}{}^2\text{S}$ with molar ratios of 10:1, 1:1 and 1:10, and silver sulfide are investigated by using solution contacts and a computer-controlled automatic measuring system. As membrane bulk impedances were commensurable with those of contacting solutions, special regression methods were necessary for evaluation. Typical resistivities were, in the order indicated above, as follows: 14, 2, 0.3, 0.1 and 0.1 kΩ cm, respectively. Thus, mixing of silver sulfide into the silver iodide matrix decreases dramatically the membrane resistance. These measured bulk membrane resistances are not affected by changes in composition and concentration of bathing solutions, and even the low-frequencies parts of impedance plots were not influenced by different stirring conditions, even in presence of corroding solutions such as thiosulfate or cyanide. Sorption also had no manifest effect on the impedance characteristics, but increasing pressure during membrane preparation or heat treatment significantly increased membrane resistances.     

A study of cadmium sulfide nanocrystalline films by grazing incidence X-ray diffraction

Thin cadmium sulfide films were prepared on a monocrystalline-crystal silicon substrate by chemical deposition from aqueous solutions. Grazing incidence X-ray diffraction revealed that the cadmium sulfide films are comprised of nanocrystal particles, with 80% of the particles having a size of 5 ± 1 nm. Some nanocrystals have a wurtzite structure, while others, a sphalerite one. The presence of cubic phase in the films is indicative of a nonequilibrium state of the nanocrystalline films. Thirty minutes after the onset of the formation of cadmium sulfide, the size and crystal structure of the constituent particles of the film become independent of the deposition time—only the film thickness increases. In addition, the initial stage of the formation of the cadmium sulfide film is accompanied by the deposition of cadmium hydroxide Cd(OH)₂.     

Structure and conformational properties of diacetyl sulfide in the gaseous and condensed phases explored by gas electron diffraction, single-crystal X-ray diffraction, vibrational spectroscopy, and quantum chemical calculations.

On the evidence of the electron diffraction pattern of the vapor, of the IR spectrum of the matrix-isolated molecule, and of quantum chemical calculations, the diacetyl sulfide molecule, CH3C(O)SC(O)CH3, adopts a planar heavy-atom skeleton with the [sp,ap] conformation. Other conformations contribute little (<1%) to the population of the gaseous molecules at normal temperatures. Salient structural parameters (r(a) structure, distances (in A), angles (in deg), and 3sigma uncertainties in parentheses) were as follows: r(C=O) 1.198(2)/1.196(2), r(C-S) 1.787(3)/1.808(3), r(C-C) 1.483(4)/1.472(4), angleC-S-C 108.8(9), angleS-C=O 125.7(6)/115.1(6), and angleS-C-C 121.1(7)/111.2(7). The structure of a single crystal at 150 K [monoclinic, P2(1)/n, a = 4.2230(7) A, b = 11.2105(17) A, c = 12.332(2) A, beta = 94.544(16) degrees] also reveals planar molecules with the same conformation and dimensions close to those of the gaseous molecule. Changes in the vibrational spectra of the compound accompanying the transition from the vapor to the condensed phases are attributed not to the presence of more than one conformer but to differences in the local environment of the two carbonyl groups. The properties deduced are compared with those of other compounds of the type CH3C(O)XC(O)CH3 (X = CH2, NH, or O).     

X-ray diffraction measurements on PE 2000 between 10 K and 300

Summary It was possible to obtain film exposures of the WAXS-diagram (2 50°) of a PE-fraction in the temperature range from 10 K to 300 K by using a special low temperature Guinier-chamber. The crystallographica-,b-andc-axis has been calculated from the positions of all reflexions. The different behaviour of their expansion coefficients can be explained by activation of rotational- and torsional-vibrations. If we take the number of net planes as constant and consider a temperature-independent part resulting from paracrystalline disorder (built up during crystallization), we can describe the linear increasing of the integral widths of the reflexions with decreasing temperature (10 ... 100%) with building up of inherent stresses inside the crystals.

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Zusammenfassung Eine spezielle Tieftemperatur-Guinier-Kammer ermöglichte es, Filmaufnahmen der Röntgenweitwinkelstreukurve (2 50°) einer hochkristallinen Polyäthylen-Fraktion im Bereich von ca. 10 K bis 300 K zu erhalten. Das unterschiedliche Temperaturverhalten der Ausdehnungskoeffizienten der kristallographischena-,b- undc-Achse, berechnet aus der Lage aller auswertbaren Reflexe, kann durch Anregung von Torsions- und Rotationsschwingungen erklärt werden. Unter der Annahme konstanter Kristallitgrößen sowie eines temperaturunabhängigen parakristallinen Gitterstörungsanteils (hervorgerufen durch Defekteinbau bei der Kristallisation), kann die starke Zunahme der integralen Breiten der Reflexe (bis ca. 100%) zu tiefen Temperaturen auf Eigenspannungen in den Kristalliten zurückgeführt werden.

     

Simultaneous small-angle X-ray scattering and wide-angle X-ray diffraction

The simultaneous SAXS/WAXD technique is shown to provide an unambiguous method for following structural changes taking place during the programmed heating of a range of multiphase polymeric materials. Results are given for polyethylene, block copolyurethanes and block copolyesters containing liquid crystalline hard segments. UK Thermal methods Group Award Lecture     

Preliminary in situ X-ray diffraction measurements of UV-induced photomechanical effects in a mesogenic material

The aim of this work was to determine by X-ray diffraction the nature of the UV-induced changes in the smectic C* organization of a calamitic liquid crystalline material containing the UV-sensitive azobenzene group in the rigid core moiety. As a result of the reversible trans-cis-isomerization, a decrease of all transition temperatures (1.1°C for the SmA-SmC* transition) was observed. In the SmC* phase, this corresponds to an increase in layer spacing (up to 0.5 Å); in the SmA phase, the detected increase in layer spacing was less than a tenth of this. The increase in layer spacing is interpreted in terms of molecules in the cis- configuration expelled from the smectic layers.     

Determination of the optimum Eu3+-concentration in LaAlO3:Euphosphors by X-ray diffraction and fluorescence measurements

Combining X-ray powder diffraction with fluorescence measurements is an efficient way to determine the optimum activator concentration of inorganic phosphors. La_1?xEu_xAlO₃ samples (perowskite structure), prepared by solid state reactions with 0.5<x<5.0 at 1480 K, were investigated by both analytical methods. The luminescence emission spectra show strong ⁵D₀-⁷F₁ and ⁵D₀-⁷D₂ transitions and fluorescence intensity reaches a maximum at 1 mol% Eu³⁺. X-ray diffraction shows the formation of an EuAlO₃ phase at Eu³⁺ concentration above 1 mol%. Below 1 mol%, Eu³⁺ substitutes for La³⁺, as can be seen from the change in the lattice constant c.     

Liquid structures of 1-butyl-3-methylimidazolium tetrafluoroborate and carbon dioxide mixtures by X-ray diffraction measurements

X-ray diffraction measurements for the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate, [BMIM][BF₄], mixed with CO₂ were carried out at high pressures using our developed polymer cell. The intermolecular distribution functions obtained for [BMIM][BF₄]–CO₂ mixtures showed that CO₂ molecules are preferentially solvated to the [BF₄]⁻ anion. The similar preferential solvation was previously observed in analogous 1-btuyl-3-methylimidazolium hexafluorophosphate, [BMIM][PF₆], with a different anion, which is in harmony with the present results in [BMIM][BF₄]–CO₂.     

Synthesis, X-ray diffraction studies, and DFT calculations on hexacoordinated germanium derivatives: the case of germaspirobis(ocanes)

Synthesis of the title compounds, viz. [RN(CH2CHR'O)2]2Ge (1, R = Me, R' = H; 2, R = Me, R' = Ph; 3, R = Ph, R' = H), by the reaction of 2 equiv of corresponding dialkanolamines RN(CH2CHR'OH)2 (4, R = Me, R' = H; 5, R = Me, R' = Ph; 6, R = Ph, R' = H) with (AlkO)4Ge is reported. Composition and structures of all novel compounds were established by 1H and 13C NMR spectroscopy and mass spectrometry as well as elemental analysis data. The single-crystal X-ray diffraction of 2 has clearly indicated the presence of two transannular interactions Ge<--N in the compound. N atoms are cis-orientated. The compound 3 possesses long Ge...N distances. The structural data obtained from geometry optimizations by DFT calculations on 1-3 reproduces experimental results. Both cis- and trans-isomers were studied, and cis-configuration was found to be more thermodynamically stable for all three compounds. The transition states for possible cis <--> trans rearrangement processes in 1-3 were calculated. The properties of the Ge-O and Ge<--N bonds in 1-3 were analyzed by the AIM approach. The interactions between the Ge atom and N atoms as well as O atoms possess predominantly ionic character.     

The molecular structure of tris-2,2,6,6-tetramethyl-heptane-3,5-dione aluminium: gas-phase electron diffraction,quantum chemical calculations and X-ray crystallography

Structural Chemistry - The molecular structure of tris-2,2,6,6-tetramethyl-heptane-3,5-dione aluminium, or Al(thd)3, has been determined by quantum chemical (DFT) calculations, X-ray...     

Insights into post-annealing and silver doping effects on the internal microstructure of ZnO nanoparticles through X-ray diffraction probe

ZnO nanoparticles were synthesized via Pechini method at various post-annealing temperatures (400°, 500°, and 600 °C) and silver doping concentrations (Zn:Ag molar ratios of 30, 20, and 10). Multifarious microstructural features including crystallite size, size-strain based broadening, residual stress, preferential orientation, crystallinity degree, lattice parameters, unit cell variation, and stacking fault probability were surveyed through phase analysis, Williamson-Hall plot, texture coefficient and unit cell calculations. X-ray probing verified good crystallinity with a hexagonal close pack Wurtzite morphology. Williamson-Hall analysis exhibited distributions of crystallite size and microstrain as well as their contributions on the line broadening of the host ZnO and guest Ag phases upon annealing-doping treatments. Textural analysis revealed the alteration in anisotropic crystallinity of the host phase and transformation of the preferred directions, (100) and (101), as function of annealing-doping processes. Besides, while guest Ag phase was shown to be polycrystalline with randomly orientated crystals at moderate concentration with respect to thermal treatment, preferential orientation went through a major change, (220) to (111), with increment in Ag loadings. Under identical synthetic conditions, the distinction in the lattice constants and unit cell variation between pure and doped ZnO nanoparticles was enforced and results verified major impressionability via annealing and doping factors.     

X-ray diffraction relaxation of polyethylene

The change in x-ray diffraction intensity with time following rapid stretching by various amounts is measured for a low-density polyethylene sample at several temperatures. An appreciable decrease in intensity with time at the meridian of the diffraction from the 110 and 200 planes is observed to occur within the first 5 sec following stretching. The change takes considerably longer times at lower temperatures. By use of a calibration curve, the change in crystal orientation functions for the a, b, and c crystal axes were calculated, and an increase in c-axis orientation was shown. From the results of birerringence measurements on the same sample, the crystalline and amorphous contributions to birefringence were calculated. It was shown that stretching is initially accompanied by a greater amount of amorphous than crystalline orientation, and that relaxation involves an increase in crystalline orientation accompanied by a decrease in amorphous orientation.