An X-ray diffraction study of mesoionic 1-thia-2,3,4-triazolo-5-aminidine and some of its derivatives

X-ray diffraction data are presented for the title mesoionic compound (I), its hydrochloride salt (II) and methylated derivative (III). The crystal of (I) is orthorombic, space group P2₁2₁2₁, with cell dimensions: a = 5.857(1) Å, b = 12.494(2) Å, c = 16.328(3) Å, with four molecules per unit cell. The crystal of (II) is monoclinic, space group P2₁/n, with cell dimensions: a = 5.5720(10) Å, b = 21.5770(4) Å, c = 11.2330(2) Å, beta = 95.15(3)°, with four molecules per unit cell. The crystal of (III) is monoclinic, space group P2₁/n, with cell dimensions: a = 12.0886(5) Å, b = 7.9103(4), c = 104.29(1) Å, beta = 104.29(1)°, with four molecules per unit cell. Of particular interest is the fact that the C5–N6 bond appears to have a high double bond character in all three of the compounds studied. In addition, it is found that the exocyclic N-phenyl group changes from being in the cis conformation with respect to sulfur in compounds (I) and (III) to the trans conformation in the hydrochloric salt (II).     

An X-ray study of some 2,3-diphenyltetrazolium salts

An X-ray diffraction study is reported for three molecules of salts containing a cation with a positive charged 2,3-diphenyltetrazolium ring. The results confirm aromatic structure of the tetrazole ring and the delocalization of charge on the whole molecules of the cations. The molecular geometry obtained is compared with that for free mesoionic 2,3-diphenyltetrazoles which have already been studied and the ring parameters do not reveal significant differences. But is shows that the geometry of the (NNO)^– exocyclic group is changed as a result of alkylation. Compound I C₁₃H₁₂N₅Cl, P2₁/a,a=16.934(4),b=6.575(1),c=26.121(4) Å, =108.15(2)°, II C₁₄H₁₃N₆OI, P3₁2,a=10.774(3),c=12.821(4) Å, IV C₂₆H₂₀N₈Cl₂, C2/c,a=22.316(4),b=6.6903(7),c=20.437(3) Å, =92.51(1)°.     

X-ray diffraction study of some indolinones

X-ray diffraction studies are reported for six indolinones. The results show that two different types of associates are present in the crystal state of the compounds having an NH group. The indolinone molecules without any substituents form cyclic dimers while those with one or two methyl groups attached to the C3 atom of the lactam ring form infinite hydrogen bonded chains. It is confirmed that the lactam moiety forms a typical planar amide structure with no sign of the enol form present.     

An X-ray diffraction study of sodium borate glasses

X-ray diffraction measurements have been performed on two pairs of sodium borate glasses of differing compositions. Glasses of given composition were obtained with two different thermal histories. The radial distribution functions of samples of the same composition appear similar. The short range order is not affected by the range of quenching rates explored.     

X-ray diffraction study of thiocarbamide hydrochloride

Thiocarbamide hydrochloride single crystals forming a salt with the composition [(NH₂)₂CSH]⁺Cl^? are studied by the X-ray diffraction method. The tetragonal crystals have the unit-cell parameters a = 7.556(1) Å and c = 18.329(3) Å, V = 1046.5 ų, Z = 8, ρ_calcd = 1.436 g/cm³, sp. gr. P4₁2₁2, and R = 0.050. Each chloride anion in the crystal forms five hydrogen bonds with thee different cations.     

X-ray powder diffraction study of polytetrafluoroethylene

Samples of polytetrafluoroethylene were studied by X-ray diffraction. A quantitative X-ray powder diffraction analysis of three components of the polymer was performed for the first time. All samples of polytetrafluoroethylene were found to be three-phase and consist of one crystalline and two amorphous phases. One of the amorphous phases is composed of low-molecular-weight products. The structure of the latter phase was established for the first time by X-ray diffraction methods and computer simulation.     

X-ray diffraction study on amorphous gallium

Amorphous films of some μm in thickness, prepared by low temperature condensation in an ultra-high vacuum onto liquid helium cooled substrates, have been studied in situ by using an X-ray diffractometer operating in a symmetrical reflection mode. The structure factor of gallium has been obtained over the wavevector range 1.3 to 16.1 Å⁻ by means of two wavelengths, Cr_K and Mo_K, monochromatized by balanced filters. The average number of nearest neighbours deduced from the well-resolved first maximum in the radial distribution function is equal to 9.3 atoms. The results are compared to those previously found by electron diffraction measurements on thin films and also to the structure of supercooled liquid.     

X-ray diffraction study of mesophase bitemplate-containing silicas

The effect of the composition of a bitemplate (solubilization) mixture on the formation of a spatially organized structure of mesophase siliceous systems has been investigated by X-ray diffraction. Alkylpyridinium halides (C _n PyHal with n = 8?16 (counterion Cl) and 18 (counterion Br)) were used a solubilizator, and monoethanolamides (EAC _m ) of saturated n-aliphatic acids (m = 10?16) and trialkylphosphine oxides (H_{2e + 1}C _e )₃PO, where e = 8, 10, or 12, were used as solubilizates. Differences in the mesophase structure of template-containing silicas synthesized in aqueous and aqueous salt (NaCl) solutions have been revealed. It is shown that the type and degree of ordering of the silica mesophase structure depends on the nature, spatial organization, and the solubilizator and solubilizate concentrations.     

An X-ray diffraction study of the structure of barium fluorozirconate and fluorohafnate glasses

Two binary glasses have been prepared in the ZrF₄BaF₂ and HfF₄BaF₂ systems, containing 64 mol.% ZrF₄ and 66 mol.% HfF₄, respectively. The two plate-like glass samples were studied by X-ray diffraction, and the resulting data were subjected to a Fourier analysis. The pair correlation functions thus obtained yield a ZrF (or HfF) nearest neighbor coordination number of ～ 7.6 for both glasses. The second peak in the correlation functions has been assigned to a combination of FF and BaF interactions, while the third peak is probably due in part to ZrZr (Hf-Hf) interactions. The diffraction data have been compared with the predictions of structural models for barium fluorozirconate and fluorohafnate glasses.     

An X-ray diffraction study of the amorphous structure of chemically vapor-deposited silicon nitride

X-ray diffraction measurements have been carried out for two kinds of samples of CVD-amorphous silicon nitride with different values of the density. From radial distribution analysis, it became clear that the short range structure in these samples resembles that of the crystalline β-phase. Coloring in CVD-amorphous Si₃N₄ was found to be induced by X-ray irradiation. Based on the deficient numbers of the first nearest neighbours in SiN bondings, it was proposed that CVD-amorphous Si₃N₄ consists of small clusters including vacancies in their matrix.     

X-ray diffraction study of gadolinium stearate Langmuir-Blodgett films

The comparative structural studies of gadolinium stearate Langmuir-Blodgett films prepared with the use of two different subphases (aqueous solutions of gadolinium chloride and gadolinium acetate) have been performed by the methods of X-ray diffractometry. The films were applied onto single-crystal silicon substrates coated with a native-oxide layer either with the use of buffer molecular stearic-acid layers or without such layers. It was established that the films obtained with the use of gadolinium acetate and the preliminarily formed buffer layers are, in fact, single-phase Y-type films with highly ordered molecular structure, and the thickness of the bimolecular layer d = (51.3 ± 0.5) Å.     

X-ray diffraction study of defects in zinc-diffusion-doped silicon

Samples of CZ n-Si〈Zn〉(111) are prepared by high-temperature zinc-diffusion annealing followed by quenching and are studied by X-ray diffraction. The silicon contains an initial phosphorus impurity and zinc-compensating admixture at concentrations N _P = 1.5 × 10¹⁴ cm^?3 and N _Zn = 1 × 10¹⁴ cm^?3; i.e., the relation N _P/2 < N _Zn < N _P is fulfilled. Microdefects are studied by double- and triple-crystal X-ray diffraction in the dispersion free modes (n, ?n) and (n, ?n, +n). The samples are found to contain microdefects with two characteristic sizes (average sizes of about 1 μm and 70 nm). The interplanar distance in the near-surface layer with a thickness of 0.1 μm is smaller than this parameter in the remaining matrix, the difference being equal to d ₀ Δd/d ₀ ≈ 2 × 10^?5. This layer contains mainly vacancy-type microdefects. The angle between the reflecting planes and the local surface relief is Δψ = (7 ± 1) arcmin.     

X-ray diffraction study of highly purified human ceruloplasmin

The three-dimensional structure of ceruloplasmin (CP) with unoccupied labile metal-binding sites and the structure of CP containing Ni²⁺ in the labile sites were solved for the first time at 2.6 and 2.95 Å resolution, respectively. Crystallization was performed with the use of storage-stable CP, which was prepared in the presence of proteinase inhibitors and purified from (pre)proteinases. Ceruloplasmin with Ni²⁺ crystallized in the orthorhombic space group, which had been earlier unknown for CP. Ceruloplasmin with the unoccupied labile sites crystallized in the trigonal crystal form. The differences in intermolecular contacts observed in the trigonal and orthorhombic crystal structures of CP are considered. The conformational changes attendant upon Ni²⁺ binding are described. It was suggested that the labile sites are multifunctional and can both bind metal ions potentially toxic to organisms and be involved in electron transfer from substrates to the active site.     

X-ray diffraction and X-ray standing-wave study of the lead stearate film structure

A new approach to the study of the structural quality of crystals is proposed. It is based on the use of X-ray standing-wave method without measuring secondary processes and considers the multiwave interaction of diffraction reflections corresponding to different harmonics of the same crystallographic reflection. A theory of multiwave X-ray diffraction is developed to calculate the rocking curves in the X-ray diffraction scheme under consideration for a long-period quasi-one-dimensional crystal. This phase-sensitive method is used to study the structure of a multilayer lead stearate film on a silicon substrate. Some specific structural features are revealed for the surface layer of the thin film, which are most likely due to the tilt of the upper layer molecules with respect to the external normal to the film surface.     

X-ray diffraction study of the structure of detonation nanodiamonds

The spatial structure of aggregates formed by detonation nanodiamonds is investigated using the wide-angle and small-angle X-ray scattering techniques. The effective sizes of crystallites and the crystallite size distribution function are determined. The shape of scattering aggregates is restored from the small-angle X-ray scattering data. An analysis of the results obtained allowed the conclusion that the nanodiamond aggregates have an extended spatial structure composed of nine to ten clusters, each involving four to five crystallites with a crystal lattice of the diamond type.     

X-ray diffraction study of short-period AlN/GaN superlattices

The structure of short-period hexagonal GaN/AlN superlattices (SLs) has been investigated by X-ray diffraction. The samples have been grown by metalorganic vapor-phase epitaxy (MOVPE) in a horizontal reactor at a temperature of 1050°C on (0001)Al₂O₃ substrates using GaN and AlN buffer layers. The SL period changes from 2 to 6 nm, and the thickness of the structure varies in a range from 0.3 to 1 μm. The complex of X-ray diffraction techniques includes a measurement of θ-2θ rocking curves of symmetric Bragg reflection, the construction of intensity maps for asymmetric reflections, a measurement and analysis of peak broadenings in different diffraction geometries, a precise measurement of lattice parameters, and the determination of radii of curvature. The thickness and strain of separate SL layers are determined by measuring the θ-2θ rocking curves subsequent simulation. It is shown that most SL samples are completely relaxed as a whole. At the same time, relaxation is absent between sublayers, which is why strains in the AlN and GaN sublayers (on the order of 1.2 × 10^?2) have different signs. An analysis of diffraction peak half-widths allows us to determine the densities of individual sets of dislocations and observe their change from buffer layers to SLs.     

X-ray diffraction and IR spectroscopy study of labuntsovite-group minerals

The distribution of cations over the positions in the structures of labuntsovite-group minerals was studied by X-ray diffraction analysis and IR spectroscopy. Several types of cation order over the five key positions are established depending on cation composition and their force characteristics.     

Low temperature X-ray diffraction study of CdI2 crystals

Solid state structural transformations in polytypic crystals of cadmium iodide have been investigated at low temperatures using X-ray diffraction techniques. The crystals were cooled to liquid nitrogen and liquid helium temperatures employing three different methods. The results obtained are discussed on the basis of bond dissociation energies of interlayer and intralayer bonds and the possible mode of layer displacements in MX₂-type polytypic crystals.     

An X-ray diffraction refinement of the structure of natural thomsonite

Thomsonite Na₂Ca₄Al₁₀Si₁₀O₄₀, orthorhombic Pncn, a = 1.3124 nm, b = 1.3078 nm, c = 0.662 nm, V = 1.1369 nm³, Z = 2, D_m = 2.30, D_c = 2.26, μ = 12.4 cm⁻¹. The average length of the bond T–O = 0.1685 nm. The final R-value for 456 independent observed reflections is 0.085.