The crystal structure of hcc-CuAsSe

The crystal structure of synthetic copper arsenic selenide CuAsSe, has been determined by a three-dimensional single-crystal X-ray examination using film data. The crystals, of orthorhombic space group Pbcn, have Z = 24 in a unit cell of dimensions a = 11.75 ± 0.02, b = 6.79 ± 0.01, and c = 19.21 ± 0.03 Å. The structure was solved by Patterson projection and electron density methods and isotropically refined to R = 0.125 for 300 observed reflections. The structure of CuAsSe is related to the B6 structure of 6H ZnS as CuAsS is to the B3 structure of zincblende. Alternately in Jagodzinski nomenclature CuAsSe has hcc packing rather than ccc packing of CuAsS.     

Crystal structure of RbOsO3N: A new CsReO4-type compound

Crystals of RbOsO₃N are orthorhombic, space group Pnma, with z = 4, a = 5.571(1), b = 5.794(1), c = 13.735(3), Å. Intensities for 556 independent reflections collected on a four-circle diffractometer were used in the structure determination and the structure was refined to a final R value = 0.046 (R_w = 0.056). The structure consists of OsO₃N discrete tetrahedra linked together by 8-coordinated Rb ions. The oxygen and nitrogen atoms are distributed randomly. RbOsO₃N is the first compound belonging to the CsReO₄-type family for which the complete structure has been determined. This structure can be related to scheelite type but appreciable differences occur in tetrahedra arrangement.     

Ternary phases MPtSi (M = Ca,Eu, Sr,Ba) with the LalrSi-type structure

Four ternary phases MPtSi (M = Ca, Eu, Sr, Ba) have been shown to crystallize in the LaIrSi-type structure (space group P2₁3). This ternary structure is a derivative structure of the binary SrSi₂-type structure (space group P4₃32 or P4₁32). In the MPtSi series the LaIrSi-type structure has a stability range for metals with radii from r_Ca = 1.973 Å to r_Ba = 2.243 Å in contrast to MSi₂ compounds which exist with the SrSi₂-type structure only from r_Sr = 2.151Å to r_Ba 2.243 Å. From a single-crystal investigation on CaPtSi remarkably short PtSi distances of 2.30 Å (3x) are obtained. Structural relations are discussed.     

Recent advances in surface x-ray diffraction and the potential for determining structure-sensitivity relations in single-crystal electrocatalysis

Determining how electrode structure governs the performance of an electrocatalyst requires techniques capable of probing structure at the atomic scale, often in situ and operando. In recent years, there have been numerous advances in the main experimental techniques for determining the structure of the electrochemical interface. In situ/operando synchrotron surface x-ray diffraction measurements are key to investigate the atomic structure of the electrode surfaces as well as understand the structure-reactivity relations in electrocatalysis. Here we discuss some recent improvements that have taken place in surface x-ray diffraction and how we expect them to lead to an enhanced understanding of electrocatalysis.     

N,N′ di n-hexyladipamide,a model for nylon 6,6

During research on model molecular compounds for synthetic polyamides, the crystal structure of N,N′ di n-hexyladipamide (NNDHA) has been determined by single crystal X-ray diffraction. The structure was solved by direct methods and refined to a final R value of 0.054. The molecule has an all-trans planar conformation. The packing consists of layers of molecules linked by hydrogen bonds in c direction. Molecular structure and packing resemble closely those reported for polyhexamethylenadipamide (nylon 6,6).     

A Novel Boron-Rich Scandium Borocarbide; Sc4.5−xB57−y+zC3.5−z(x=0.27, y=1.1, z=0.2)

A novel ternary boron-rich scandium borocarbide Sc_4.5−xB_57−y+zC_3.5−z (x=0.27, y=1.1, z=0.2) was found. Single crystals were obtained by the floating zone method by adding a small amount of Si. Single-crystal structure analysis revealed that the compound has an orthorhombic structure with lattice constants of a=1.73040(6), b=1.60738(6) and c=1.44829(6) nm and space group Pbam (No. 55). The crystal composition ScB_13.3C_0.78Si_0.008 calculated from the structure analysis agreed with the measured composition of ScB_12.9C_0.72Si_0.004. The orthorhombic crystal structure is a new structure type of boron-rich borides and there are six structurally independent B₁₂ icosahedra I1—I6, one B₈/B₉ polyhedron and nine bridging sites all which interconnect each other to form a three-dimensional boron framework. The main structural feature of the boron framework structure can be understood as a layer structure where two kinds of boron icosahedron network layer L1 and L2 stack each other along the c-axis. There are seven structurally independent Sc sites in the open spaces between the boron icosahedron network layers.     

Laser-Rf double-resonance measurements of the metastable 3d 34s 5P1,2,3, 3d 24s 2 1 G 4 states of 47Ti

The hyperfine structure (hfs) of 4 metastable states of ⁴⁷Ti has been measured very precisely by a laser-rf double resonance method. The corresponding hyperfine structure constants A _exp and B _exp have supplied a set of experimental data necessary for hyperfine structure analysis and determination of Sternheimer free nuclear quadrupole moment Q.     

A structural study of a new lithium oxyfluorotungstate,LiW3O9F

The structure of LiW₃O₉F was determined from 972 single crystal reflections and refined by least squares to anRfactor of 0.065. It has orthorhombic symmetry with space groupFdd2 and parametersa = 12.716(2)A?,b = 15.230(2)A?,c = 7.288(1)A?, andZ = 8. The structure is related to the HTB structure and can be described as a complex stacking of HTB layers perpendicular to theb axis. The lithium atoms are found in the hexagonal cavities of the HTB layers.     

Crystal structures and phase stability in pseudobinary CaAl2−xZnx

Samples in the pseudobinary system CaAl_2−xZn_x (0?x?2) were synthesised from the elements. Three different structure types, the C15 and C36 Laves phase structures and the KHg₂ (CeCu₂) structure, were observed. The structures and homogeneity ranges of the underlying phases were investigated by electron microscopy and thermal analysis as well as X-ray powder diffraction. The stability ranges for the different structure types were found to be 0?x?0.18, 0.28?x?0.68 and 0.93?x?2 for the C15, C36 and KHg₂ structure types, respectively.     

Low-Temperature Crystal Structure of S-camphor Solved from Powder Synchrotron X-ray Diffraction Data by Simulated Annealing

The ordered, low-temperature crystal structure of the pure enantiomer of camphor (C₁₀H₁₆O) has been solved from high-resolution powder synchrotron X-ray diffraction data. The structure is orthorhombic, space group P2₁2₁2₁, Z=8, with a=8.9277(2) Å, b=27.0359(5) Å, and c=7.3814(1) Å at 100 K. The structure was solved by autoindexing of the pattern, space group determination, and then optimization of the positions and orientations of the two independent molecules in the unit cell by simulated annealing. The molecular structure obtained from the restrained Rietveld refinement shows reasonable agreement with that optimized from ab initio molecular orbital calculations. In the crystal structure, the molecules are aligned antiferroelectrically and weak C-H…O hydrogen bonds link together the independent molecules.     

Novel porphyrin-quinazoline conjugates via the Diels-Alder reaction

Novel derivatives of meso-tetraphenylporphyrin with appended quinazoline moieties were synthesized, via the Diels-Alder reaction, between a 4-(porphyrinyl)pyrimidine ortho-quinodimethane and 1,4-benzoquinone, 1,4-naphthoquinone and N-(p-nitrophenyl)maleimide. The structure of one bis adduct was established by X-ray crystallography and mass spectrometry. We have unequivocally confirmed that the 2:1 adducts obtained from the reaction of pyrimidine-fused 3-sulfolenes with N-arylmaleimides have an open-chain structure and not a cyclooctapyrimidine structure, as previously published.     

Phase transition and thermodynamic properties of TiN under pressure via first-principles calculations

The phase transition of TiN from the NaCl structure to the CsCl structure is investigated by the first-principles plane wave pseudopotential density functional theory method, and the thermodynamic properties of the NaCl structures are obtained through the quasi-harmonic Debye model. It is found that the pressures for transition from the NaCl structure to the CsCl structure are 364.1 GPa (for GGA) and 322.2 (for LDA) from equal enthalpies. The calculated ground state properties such as equilibrium lattice constant, bulk modulus, and its pressure derivative are in good agreement with experimental and theoretical data of others. Moreover, the dependences of the relative volume V/V ₀ on the pressure P, the Debye temperature ?? _D , and heat capacity C _V on the pressure P and temperature T, as well as the variation of the thermal expansion ?? with temperature and pressure are also successfully obtained.     

Analysis of phase structure and evolution of PP/PEOc blends during quiescent molten-state annealing process from SEM patterns. Part II. Co-continuous morphology

The influence of quiescent molten-state annealing process on the phase structure and morphology of poly(propylene)/poly(ethylene-co-octene) blends with co-continuous morphology was studied using scanning electron microscopy (SEM). The structure parameter called characteristic length (L) was calculated by the pattern analysis of SEM micrographs to describe morphological variation with annealing time during molten-state annealing process under quiescent condition. Moreover, the potential fractal behavior of the phase structure and morphology of PP/PEOc?=?50/50 blend during the process were discussed. The histograms of P(L/L _m ) obtained at various annealing time fell on a master curve, demonstrating the self-similar growth of the phase structure of the blends during quiescent molten-state annealing process.     

The crystal structure of “Ba2Fe4S5”: A two-dimensional array of FeS4 tetrahedra

The crystal structure of a compound with a nominal composition Ba₂Fe₄S₅ was determined from 432 observed structure amplitudes. The lattice constants are a = 4.016(2), Å, b = 9.616(4), Å, c = 6.514(4), Å, Pmmn, Z = 1. The structure consists of BaS₆ trigonal prisms that share triangular faces to form infinite columns parallel to a. Zig-zag chains of Fe are formed parallel to b by filling the tetrahedral interstices. The structure can also be viewed as an infinite two-dimensional plane of FeS₄ tetrahedra formed by the sharing of two edges of a face in the ±a directions and connecting by corner sharing in the ±b directions. The Ba are in the trigonal prismatic interstices. The apical sulfur atom shows an anomalously large temperature factor and has a 50% site occupancy. On the basis of full occupancy of that site the composition corresponds to BaFe₂S₃. This structure is closely related to the previously reported BaFe₂S₃ and may be an averaged structure due to twinning of a polymorph of BaFe₂S₃.     

Crystal and molecular structure of (π-methallyl)(2-(R,S)-α-phenylethylimino-3-penten-4-olato)palladium(II)

The crystal structure of the compound (π-methallyl)(2-(R,S)-α-phenylethylimino-3-penten-4-olato)palladium(II) has been determined. The complex crystallizes in the monoclinic system, space group P2₁/c with a=9.85, b=10.35, c=19.34 Å and β=124°13′. The structure has been solved by Patterson and Fourier methods and refined to an R factor of 0.056 using 1021 independent reflections measured with counter techniques (Mo-Kα). The chelating ring presents a localized electronic structure and the coordination of the metal atom is distorted square planar.     

Adsorption of triangular-shaped molecules with directional nearest-neighbor interactions on a triangular lattice

Using Monte Carlo and transfer-matrix methods the lattice gas model of adsorption of triangular-shaped molecules on a triangular lattice is studied. The constructed model takes into account the directionality of pairwise nearest-neighbor interactions between the adsorbed molecules. It is shown that a predominant character of "tip-to-tip" attractive interactions w ₁ always leads to the formation of the honeycomb structure in the adsorption monolayer with local density ρ = 0.66(6). While, the values of "side-to-side" w ₂ and "tip-to-side" w ₃ interactions define the structure of close-packed phase. Depending on the values of the interactions the close-packed phase may have: (a) completely disordered structure; (b) frustrated honeycomb structure which is formed by Langmuir like adsorption onto 2D pores of the honeycomb structure; (c) ordered close-packed structure consisted of the molecules which all have the same orientation relative to each other and relative to the surface.     

Synthesis of a proposed structure for the diffusible extracellular factor of Xanthomonas campestris pv. campestris

A proposed structure for the diffusible extracellular factor (DF) of Xanthomonas campestris pv. campestris (Xcc) has been synthesized. Its MS spectrum and biological activity, however, contradict those of the natural product previously reported, suggesting that the structure for DF of Xcc must be reexamined.     

Test of advanced hyperfine structure theory by precision radio-frequency and laser spectroscopy in molybdenum

The hyperfine structure splittings of 32 even parity states and of 26 odd partity states of molybdenum have been measured by atomic beam magnetic resonance and by laser induced fluorescence. The analysis of the hyperfine structure data of the even parity configurations (4d+5s)⁶ yields experimental evidence for second order hyperfine interactions. In addition, theg _J factors of 19 fine structure levels have been determined in order to test the quality of intermediate coupling wave functions for the (4d+5s)⁶ configurations.     

CdS and CdSe quantum dots subsectionally sensitized solar cells using a novel double-layer ZnO nanorod arrays

We report a novel approach for synthesizing CdS and CdSe quantum dots subsectionally sensitized double-layer ZnO nanorods for solar cells, which are comprised of CdS QDs-sensitized bottom-layer ZnO NRs and CdSe QDs-sensitized top-layer ZnO NRs. X-ray diffraction study and scanning electron microscopy analysis indicate that the solar cells of subsectionally sensitized double-layer ZnO NRs, which are the hexagonal wurtzite crystal structure, have been successfully achieved. The novel structure enlarged the range of absorbed light and enhanced the absorption intensity of light. The I-V characteristics show that the double-layer structure improved both the current density (J_sc) and fill factor (FF) by 50%, respectively, and power conversion efficiency (η) was increased to twice in comparison with the CdS QDs-sensitized structure.     

Preparation and properties of the system Fe1−xVxNbO4

Members of the system Fe_1?xV_xNbO₄ were prepared and their crystallographic, electrical, and magnetic properties were determined. The wolframite structure is formed for x ≤ 0.2, but for x ≥ 0.4, a phase transformation to the rutile structure takes place. Magnetic studies established the formal valencies of the elements for members crystallizing with the wolframite phase. However, similar analyses of compounds with the rutile structure did not provide a unique assignment of the formal valencies.