Cluster self-organization of intermetallic systems: Quasi-spherical nanocluster precursors with internal Friauf polyhedra (A-172) and icosahedra (B-137) in the Li19Na8Ba15 (hP842) crystal structure

A combinatorial and topological analysis of Li₁₉Na₈Ba₁₅ (hP842, a = 20 ?, c = 93 ?, V = 33552 ?³, P $ \bar 3 $ \bar 3 ) has been performed using computer methods (the TOPOS program package). Two types of crystal-forming quasi-spherical nanoclusters about 20 ? in diameter with internal Friauf polyhedra (A-172) and icosahedra (B-137) have been established by the complete decomposition of the 3D factor graph of the structure into cluster substructures. Each type of nanoclusters forms close-packed 2D layers 3⁶, which alternate along the c axis. The B-137 and A-172 nanoclusters are composed of three layers and have shell compositions (1 + 12 + 32 + 92) and (1 + 16 + 59 + 103) with local symmetries 3 and $ \bar 3 $ \bar 3 , respectively; they were revealed for the first time in crystal structures as cluster precursors. The icosahedral B-137 nanocluster contains a 104-atom quasicrystal approximant (Samson cluster).     

Effect of sapphire substrate orientation on the surface morphology and structural quality of thick GaN layers grown by hydride vapor phase epitaxy

The effect of substrate orientation on the surface orientation of thick GaN layers grown by hydride vapor phase epitaxy (HVPE) has been established. Layers oriented along the (0001), (11$ \bar 2 $ \bar 2 0), and (10$ \bar 1 $ \bar 1 3) planes have been obtained on, respectively, c- and a-, r-, and m-oriented substrates. Depending on the orientation of the GaN layer surface, surface defects (terraces and growth pits) are faceted by different planes whose intersections with the growth surface are perpendicular to the direction of growth pit faces. It is found that the sapphire substrate surface orientation has an effect on the layer structural quality (which increases with an increase in the layer thickness, regardless of the layer orientation). The directions of crack propagation in the GaN layer also depend on the surface orientation of the layer and are mainly determined by the intersections of the {1$ \bar 1 $ \bar 1 00} planes of the layer with the surface.     

The structure of the scandium iodide complex with antipyrine (AP) and its comparison with the structure of nonisostructural analogues (Compounds [Ln(AP)6]I3 (Ln = La, Y, or Eu))

An X-ray diffraction study of the scandium iodide complex with antipyrine [Sc(AP)₆]I₃ (AP is antipyrine, i.e., 2,3-dimethyl-1-phenyl-3-pyrazolin-5-one) (I), which is not isostructural to the analogous compounds of Y, La, and Eu (II), is performed. Crystals I are trigonal; a = 24.911 ? and c = 10.140 ?; Z = 3, space group P $ \bar 3 $ \bar 3 . Crystal I is built of [Sc(AP)₆]³⁺ complex cations of two types and I⁻ anions. In both cations, the Sc atom is octahedrally coordinated by six O atoms of six AP ligands (Sc-O, 2.054–2.078 ?). Complexes I differ from II by the absence of π-π stacking interactions between AP molecules, resulting in a supramolecular cation. Complex cations I of both types form combined layers. All I⁻ anions are located in the interlayer space, being statistically disordered within a flat area limited by eight complex cations of Sc1 and Sc2.     

Growth of congruently melting Ca0.59Sr0.41F2 crystals and study of their properties

Homogeneous crystals of Ca_0.59Sr_0.41F₂ alloy (sp. gr., Fm $ \bar 3 $ \bar 3 m, a = 0.56057 nm), corresponding to the point of minimum in the melting curve in the CaF₂-SrF₂ phase diagram, have been grown by the vertical Bridgman method. The optical, mechanical, electrical, and thermophysical properties of Ca_0.59Sr_0.41F₂ and MF₂ crystals (M = Ca, Sr) have been studied and comparatively analyzed. Ca_0.59Sr_0.41F₂ crystals are transparent in the range of 0.133–11.5 μm, have refractive index n _D = 1.436, microhardness H _μ = 2.63 ± 0.10 GPa, ion conductivity σ = 5 × 10⁻⁵ S/cm at 825 K, and thermal conductivity k = 4.0 W m⁻¹ K⁻¹ at 300 K. It is shown that the optical properties of Ca_0.59Sr_0.41F₂ crystals are intermediate between those of CaF₂ and SrF₂, whereas their mechanical and electrical characteristics are better than the latter compounds.     

Single crystals of the fluorite nonstoichiometric phase Eu 0.9162+ Eu 0.0843+ F2.084 (conductivity, transmission, and hardness)

The nonstoichiometric phase EuF_2+x has been obtained via the partial reduction of EuF₃ by elementary Si at 900–1100°C. Eu_0.916²⁺Eu_0.084³⁺F_2.084 (EuF_2.084) single crystals have been grown from melt by the Bridgman method in a fluorinating atmosphere. These crystals belong to the CaF₂ structure type (sp. gr. Fm $ \bar 3 $ \bar 3 m) with the cubic lattice parameter a = 5.8287(2) ?, are transparent in the spectral range of 0.5–11.3 μm, and have microhardness H _μ = 3.12 ± 0.13 GPa and ionic conductivity σ = 1.4 × 10⁻⁵ S/cm at 400°C with the ion transport activation energy E _a = 1.10 ± 0.05 eV. The physicochemical characteristics of the fluorite phases in the EuF₂ − EuF₃ systems are similar to those of the phases in the SrF₂ − EuF₃ and SrF₂ − GdF₃ systems due to the similar lattice parameters of the EuF₂ and SrF₂ components. Europium difluoride supplements the list of fluorite components MF₂ (M = Ca, Sr, Ba, Cd, Pb), which are crystal matrices for nonstoichiometric (nanostructured) fluoride materials M _{1 − x} R _x F_{2 + x} (R are rare earth elements).     

Investigation of the structural conditionality for changes in physical properties of K<Subscript>3</Subscript>H(SO<Subscript>4</Subscript>)<Subscript>2</Subscript> crystals

With the aim of elucidating the nature of anomalies in the physical properties of K₃H(SO₄)₂ crystals that arise as the temperature grows, the dielectric and optical properties of the crystals are studied, an X-ray diffraction analysis of single-crystal and polycrystalline specimens are performed, and the morphology and chemical composition are studied by scanning electron microscopy and energy-dispersive X-ray spectroscopy. As a result of the studies performed, a phase transition from the phase with the monoclinic symmetry (space group C2/c) to the phase with the trigonal symmetry (space group R $ \bar 3 $ \bar 3 m) is found in a number of K₃H(SO₄)₂ specimens at a temperature of ≈457 K, the responsibility of the dynamically disordered hydrogen-bond system for the rise of high proton conductivity in the high-temperature phases of the crystals of this family is confirmed, and data on the solid-phase reactions proceeding at high temperatures are obtained.     

Interaction of intrinsic point defects with dislocation stress fields in hcp zirconium crystal

The crystallographic, energetic, and kinetic characteristics of intrinsic point defects (vacancy-self-interstitial atom) in stable, metastable, and saddle configurations in hcp zirconium crystal have been calculated by the molecular-statics method. The spatial dependences of the interaction energies of intrinsic point defects and stress fields of rectilinear dislocations with Burgers vectors of 1/3[11$ \bar 2 $ \bar 2 0], 1/3 [11$ \bar 2 $ \bar 2 3], and [0001] have been found within the anisotropic linear theory of elasticity. The most likely trajectories of intrinsic point defects in dislocation stress fields (trajectories with minimum energy barriers for motion) have been constructed. Such trajectories result in dislocation only for the interaction of self-interstitial atoms with an edge dislocation that has a Burgers vector of 1/3 [11$ \bar 2 $ \bar 2 3].     

Crystal structure (Pb4.8Na1.2)[Si8(Si1.2B0.8)O25] with a new double tetrahedral layer and its comparison with hyttsjoeite, barisilite, benitoite, and langasite

A new lead-sodium borosilicate (Pb_4.8Na_1.2)[Si₈(Si_1.2B_0.8)O₂₅] (a = 9.5752 and c = 42.565 ?; space group R $ \bar 3 $ \bar 3 c) is synthesized under hydrothermal conditions, and its crystal structure is determined without preliminary knowledge of the chemical formula. The anionic radical of a new type is a double layer in which one of the three independent Si-tetrahedra contains an isomorphous boron admixture. Its topological relationship with the radicals in the structures of benitoite and langasite, as well as in the structures of lead silicates barisilite and hyttsjoeite, is found based on the block consisting of an octahedron and six tetrahedra. This allows one to consider that the new layer is derived from the hyttsjoeite layer by the replacement of the octahedron with two tetrahedra and the increase of the silicon fraction. Although lead atoms are located between the layers in the intersheet space, they form relatively strong bonds with silicon-oxygen layers. This structural type is a collector of heavy metals.     

Synthesis and X-ray diffraction study of (Cs0.5Ba0.25)[UO2(CH3COO)3] and Ba0.5[UO2(CH3COO)3]

Uranyl triacetate complexes (Cs_0.5Ba_0.25)[UO₂(CH₃COO)₃] (I) and Ba_0.5[UO₂(CH₃COO)₃] (II) are synthesized for the first time and their structures are determined by X-ray diffraction. Both compounds crystallize in the cubic crystal system. The crystal data are as follows: a = 17.3289(7) ?, V = 5203.7(4) ?³, space group I2₁3 and Z = 16 (I); a = 17.0515(8)?, V = 4957.8(4) ?³, space group I $ \bar 4 $ \bar 4 3d, and Z = 16 (II). In I and II, as in all uranyl triacetates studied earlier, the coordination polyhedron of the uranium atom is a hexagonal bipyramid whose vertices are occupied by the oxygen atoms of the uranyl and three acetate groups. The uranium-containing group belongs to the AB ₃⁰¹ (A = UO₂²⁺, B ⁰¹ = CH₃COO⁻) crystal chemical group of uranyl complexes. It was found that compound II is isostructural to the (Rb_0.50Ba_0.25)[UO₂(CH₃COO)₃] studied earlier.     

A novel representative {[Rb1.94(H2O,OH)3.84](H2O)0.1}{Al4(OH)4[PO4]3} in the pharmacosiderite structure type

The crystal structure of a new synthetic aluminophosphate {[Rb_1.94(H₂O,OH)_3.84](H₂O)_0.1}{Al₄(OH)₄[PO₄]₃} synthesized under mild hydrothermal conditions (T = 280°C, P = 100 atm) in the Rb₂O-Al₂O₃-P₂O₅-H₂O system is determined using X-ray diffraction (Stoe IPDS diffractometer, λMoK _α, graphite monochromator, 2θ_max = 64.33°, R = 0.032 for 312 reflections). The main crystal data are as follows: a = 7.4931(6) ?, space group P 3m, Z = 1, and ρ_calcd = 2.76 g/cm³. It is shown that the synthesized compound belongs to the pharmacosiderite structure type with a characteristic mixed open microporous framework composed of octahedra and tetrahedra. A comparative crystal chemical analysis of related phases is performed, and the chemical compositions of promising absorbents, i.e., hypothetical compounds potentially possible in the structure type under consideration, are proposed. It is established that pharmacosiderite and rhodizite are homeotypic to each other. Original Russian Text ? O.V. Yakubovich, W. Massa, O.V. Dimitrova, 2008, published in Kristallografiya, 2008, Vol. 53, No. 3, pp. 442–449.     

The resonant X-ray diffraction in Co-Åkermanite: Theory and experiment

The structural factors for X-ray resonant diffraction near the K-absorption edge of cobalt in Co-åkermanite have been calculated with allowance for the known data about its incommensurate 2D modulation. It is shown that the local symmetry of Co atoms in the basic structure does not allow any pure resonant reflections in the dipole-dipole approximation. However, pure resonant reflections of the h00 (h = 2n + 1) type are possible owing to the dipole-quadrupole contribution. The 5D formalism is used for the incommensurately modulated structure. It is shown that the displacement terms in the anisotropic tensor atomic factors could mainly contribute to the first-order satellites, providing pure resonant satellite reflections of the hhlm0 (m = 2n + 1) or h00m $\bar m$ (h = 2n + 1) types.     

Ethynyl and Propynylpyrene Inhibitors of Cytochrome P450

Abstract  

The single-crystal X-ray structures and in vivo activities of three aryl acetylenic inhibitors of cytochromes P450 1A1, 1A2, 2A6, and 2B1 have been determined and are reported herein. These are 1-ethynylpyrene, 1-propynylpyrene, and 4-propynylpyrene. To investigate electronic influences on the mechanism of enzyme inhibition, the experimental electron density distribution of 1-ethynylpyrene has been determined using low-temperature X-ray diffraction measurements, and the resulting net atomic charges compared with various theoretical calculations. A total of 82,390 reflections were measured with Mo Kα radiation to a (sinθ/λ)_max = 0.985 Å⁻¹. Averaging symmetry equivalent reflections yielded 8,889 unique reflections. A least squares refinement procedure was used in which multipole parameters were added to describe the distortions of the atomic electron distributions from spherical symmetry. A map of the model electron density distribution of 1-ethynylpyrene was obtained. Net atomic charges calculated from refined monopole population parameters yielded charges that showed that the terminal acetylenic carbon atom (C18) is more negative than the internal carbon (C17). Net atomic charges calculated by ab initio, density functional theory, and semi-empirical methods are consistent with this trend suggesting that the terminal acetylenic carbon atom is more likely to be the site of oxidation. This is consistent with the inhibition mechanism pathway that results in the formation of a reactive ketene intermediate. This is also consistent with assay results that determined that 1-ethynylpyrene acts as a mechanism-based inhibitor of P450s 1A1 and 1A2 and as a reversible inhibitor of P450 2B1. Crystallographic data: 1-ethynylpyrene, C₁₈H₁₀, P2₁/c, a = 14.571(2) Å, b = 3.9094(5) Å, c = 20.242(3) Å, β = 105.042(2)°, V = 1,113.5(2) Å³; 1-propynylpyrene, C₁₉H₁₂, P2₁/n, a = 8.970(2) Å, b = 10.136(1) Å, c = 14.080(3) Å, β = 99.77(2)°, V = 1,261.5(4) Å³; 4-propynylpyrene, C₁₉H₁₂, Pbca, a = 9.904(1) Å, b = 13.174(2) Å, c = 19.401(1) Å, V = 2,531.4(5) Å³.     

Cover Picture: Cryst. Res. Technol. 10/2009

The cover picture shows a single crystal of K₂La(NO₃)₅ · 2 H₂O grown at 38 °C from diluted HNO₃. View approximately along the polar –<$>\vec a_3<$> axis of the crystal. (see pages 1131 – 1138) (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Molybdenum and Tungsten Combined Oxidation by Dissociative Evaporation of Products during Refractory Oxides Crystal Growth from the Melt

The main chemical reactions and composition of gas and solid phases have been determined for the equimolar ratio Mo: W: O₂ = 1: 1: 2 at T = 2400 K in the pressure range of 1-1 x 10^-5 bar. It is established that the character of the main processes of combined oxidation depends significantly on the pressure and state of the oxidant (oxygen): at P > 7.52 x 10^-5 bar, oxidation reactions involve mainly molecular oxygen, whereas atomic oxygen dominates at lower pressures. At P ≥ 0.424 bar, the solid phase contains not only Mo but also MoO₂. At P = 1 x 10^-5 bar, the concentration of lower Mo and W oxides and elementary Mo and W in the gas phase sharply increases, which can negatively affect the main crystallization units.     

Crystal and molecular structure of rubidium azidotrimethylaluminate,Rb[Al(CH3)3N3]

The crystal structure of rubidium azidotrimethylaluminate has been determined from three-dimensional counter data, and refined by full-matrix least-squares techniques. The crystals belong to the monoclinic space groupP2₁/n, witha= 10.003(5),b=7.497(4),c= 11.806(5) Å, = 108.70(3) °, andD _c= 1.58 g cm⁼³ forZ=4. The finalR factor for 922 observed reflections is 0.049. The compound is not isostructural with its cesium analog. The aluminum atom is coordinated in a tetrahedral fashion, and the Al-N bond length is 1.944(8) Å.     

Defect structure and ionic conductivity of Ca1 ? xScxF2 + x (0.02 ≤ x ≤ 0.15) single crystals

Single crystals of the Ca_{1 − x} Sc _x F_{2 + x} (x = 0.106, 0.132, 0.156) solid solutions (CaF₂ structure type, space group Fm m) are investigated using X-ray diffraction. It is revealed that the crystals under investigation contain vacancies in the 8c positions and interstitial fluorine ions in the 48i positions. The coordination number of Sc³⁺ ions in the structure of the Ca_{1 −x} Sc _x F_{2 + x} solid solutions is equal to eight. The specific features of the concentration dependences of the ionic conductivity and the activation energy of ion transfer for the Ca_{1 − x} Sc _x F_{2 + x} (0.02 ≤ x ≤ 0.15) solid solutions are explained in the framework of the percolation model of conducting “defect regions.” The percolation threshold equal to 3–5 mol % ScF₃ corresponds to the model of [Ca_{14 − n} Sc _n F₆₈] octacubic clusters containing fluorine ions in the 48i positions. The ionic conductivity of the Ca_{1 − x} Sc _x F_{2 + x} solid solutions is analyzed in comparison with the change in this characteristic for the series of Ca_0.8 R _0.2F_2.2 crystals with rare-earth elements. Original Russian Text ? E.A. Sulyanova, V.N. Molchanov, N.I. Sorokin, D.N. Karimov, S.N. Sulyanov, B.P. Sobolev, 2009, published in Kristallografiya, 2009, Vol. 54, No. 4, pp. 612–622.     

X-ray diffraction studies oncis-[Ru(bpy)2(PMe3)Cl+][ClO4?] andcis-[Ru(bpy)2{PMe2(o-tol)}Cl+][ClO4?]; two ordered structures in thecis-bis(bipyridyl)chloro(phosphine)-ruthenium(II) series

The complexcis-[Ru(bpy)₂(PMe₃)Cl⁺][ClO₄ ⁻] crystallizes in space group P2₁/c andcis-[Ru(bpy)₂{PMe₂(o-tol)]Cl⁺][ClO₄ ⁻] crystallizes in space group ; each is present as a racemate and neither structure suffers from disorder. The Ru−PMe₂(o-tol) bond length of 2.324(2)? is slightly longer than the simple Ru−PMe₃ bond length of 2.310(2) ?.     

Displacements in the cationic motif of nonstoichiometric fluorite phases Ba1 − x R x F2 + x as a result of the formation of {Ba8[R 6F68–69]} clusters: I. The Ba0.78Tm0.22F2.22 crystals

The displacements of Ba²⁺ cations in the cationic motif of Ba_0.78Tm_0.22F_2.22 crystals, which are representatives of nonstoichiometric fluorite phases Ba_{1 ? x} R _x F_{2 + x} , are proved for the first time with the use of precision investigations of the fine atomic structure. It is shown that the cation displacements, like the previously revealed displacements in the anionic motif, reflect the formation of {Ba₈[R ₆F_68–69]} superclusters of structural defects with nanometer linear sizes. The Ba ²⁺ cations are displaced from the fluorite crystallographic positions 4a (space group Fm $ \bar 3 The displacements of Ba²⁺ cations in the cationic motif of Ba_0.78Tm_0.22F_2.22 crystals, which are representatives of nonstoichiometric fluorite phases Ba_{1 − x} R _x F_{2 + x} , are proved for the first time with the use of precision investigations of the fine atomic structure. It is shown that the cation displacements, like the previously revealed displacements in the anionic motif, reflect the formation of {Ba₈[R ₆F_68–69]} superclusters of structural defects with nanometer linear sizes. The Ba ²⁺ cations are displaced from the fluorite crystallographic positions 4a (space group Fm m) to the positions 32f. The static nature of the cation displacements is confirmed by the fact that these displacements are retained at a temperature of 110 K. The correctness of the interpretation of the correlation between the cation displacements and the formation of superclusters of structural defects is supported by the coincidence of the intercationic distances determined in the disordered phase Ba_0.78Tm_0.22F_2.22 with those found in the previously studied ordered phases Ba₄ R ₃F₁₇ (R = Y, Yb). The model with splitting of cationic positions is appropriate for testing in structural investigations of crystals of the fluorite phases M _{1 − x} R _x F_{2 + x} at room temperature. Original Russian Text ? A.M. Golubev, L.P. Otroshchenko, V.N. Molchanov, B.P. Sobolev, 2008, published in Kristallografiya, 2008, Vol. 53, No. 6, pp. 1023–1030.     

The Synthesis and Crystal Structure Determination of Phenyl 2-(3,4-dihydro-1(2<Emphasis Type="Italic">H</Emphasis>)naphthalenylidine)hydrazinecarboxylate and Phenyl (2,4-dichlorophenyl-methylene)hydrazinecarboxylate

Abstract  

(E)-Phenyl 2-(3,4-dihydro-1(2H)-naphthalenylidine)hydrazinecarboxylate and (E)-phenyl (2,4-dichlorophenylmethylene)hydrazinecarboxylate were prepared by the condensation of 1-tetralone or 2,4-dichlorobenzaldehyde with phenyl hydrazinecarboxylate. Crystals of C₁₇H₁₆N₂O₂ 3 are monoclinic, C2/c, a = 17.763(4) ?, b = 8.353(2) ?, c = 40.233(8) ?, Z = 16, V = 5,839(2) ?³, R ₁ = 0.0448 and wR ₂ = 0.1104 for reflections with I > 2σ(I). Crystals of C₁₄H₁₀N₂O₂Cl₂ 5 are orthorhombic, P2₁2₁2₁, a = 8.288(3) ?, b = 14.082(2) ?, c = 23.788(5) ?, Z = 8, V = 2,777(1) ?³, R ₁ = 0.0815 and wR ₂ = 0.2006 for reflections with I > 2σ(I). The molecular packing in the crystal for both compounds is the result of N–H···O hydrogen bonding.