X-ray Diffraction Study (x-ray + diffraction_study)

Distribution by Scientific Domains
Distribution within Chemistry

Kinds of X-ray Diffraction Study

  • preliminary x-ray diffraction study
  • single-crystal x-ray diffraction study


  • Selected Abstracts


    Synchrotron X-Ray Diffraction Study of ErMn2D2.

    CHEMINFORM, Issue 31 2007
    J. P. Maehlen
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source]


    On the Mechanism of the Pressure-Induced Wurtzite- to NaCl-Type Phase Transition in CdS: An X-Ray Diffraction Study.

    CHEMINFORM, Issue 14 2005
    Heidrun Sowa
    Abstract For Abstract see ChemInform Abstract in Full Text. [source]


    ChemInform Abstract: Powder X-Ray Diffraction Study of the Double Complexes [M(NH3)5Cl][M,Cl4] as Precursors of Metal Powders (M: Ir, Rh, Co; M,: Pt, Pd).

    CHEMINFORM, Issue 36 2002
    Yu. V. Shubin
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]


    ChemInform Abstract: X-Ray Diffraction Study of Ge,Bi,Te Mixed-Layer Ternary Compounds.

    CHEMINFORM, Issue 18 2001
    O. G. Karpinskii
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]


    An Energy Dispersive X-ray Diffraction Study of Dioxouranium(VI) in 1 M Lithium Citrate

    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 13 2004
    Ermanno Vasca
    Abstract An Energy Dispersive X-ray Diffraction (EDXD) study of 0.3 M dioxouranium(VI) in 1 M lithium citrate at pH = 5 is reported. The data are in accordance with the existence of a predominately polynuclear complex containing four U atoms, concluded from potentiometric measurements. The uranium atoms lie at the corners of two triangles sharing one edge. Five O atoms surround each uranyl group, the uranium coordination polyhedron being a pentagonal bipyramid; four U atoms are linked through double or single O bridges. The U,U distances are 3.95 Å and 4.65 Å. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]


    Synthesis, structural and thermal studies of tetrathioureacopper(I) chloride crystals

    CRYSTAL RESEARCH AND TECHNOLOGY, Issue 8 2005
    M. Dhandapani
    Abstract Tetrathioureacopper(I) chloride, hereafter abbreviated as TCC, was synthesised and single crystals were obtained from saturated aqueous solution by slow evaporation (solution growth) method at room temperature. The crystals obtained are bright, colourless and transparent having well defined external faces. The grown crystals were characterized through elemental analysis, single crystal X-ray diffraction study, thermal analysis, electron spin resonance spectroscopy and Fourier Transform infrared spectroscopy. The elemental analysis confirms the stoichiometry of the compound. The single crystal diffraction studies indicate that TCC crystallises in the tetragonal lattice and the unit cell parameters are a = b = 13.4082 Å, c = 13.8074 Å, V = 2482.29 Å3, , = , = , = 90°. Space group and the number of molecules per unit cell (Z) are found to be P41212 and 8 respectively. The TG curve of the sample shows a prolonged decomposition from 210 to 628.3 °C, from which the decomposition pattern has been formulated. The endothermic peaks in the DTA curve indicate melting and decomposition of the compound at 165.2 and 633.8 °C respectively. An exothermic peak in high temperature DSC indicates a phase transition in the compound at 274.8 °C. Thermal anomalies observed in the low temperature DSC at ,163.3, ,152.0, ,141.5, ,108.3, 1.0 and 12.1 °C in the heating run and ,157.1 and ,153.9 °C in the cooling run reveal first order phase transitions in the crystal. The peaks observed at ,146.2 °C in both the heating and cooling runs suggest occurrence of a second order phase transition in this compound. The IR spectroscopic data were used to assign the characteristic vibrational frequencies of various groups present in the compound. The ESR study confirms that the copper is in the +1 oxidation state in the complex. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Solubility studies on valdecoxib in the presence of carriers, cosolvents, and surfactants

    DRUG DEVELOPMENT RESEARCH, Issue 1 2004
    Kashappa Goud H. Desai
    Abstract Enhancement of the solubility of valdecoxib was examined using a series of hydrophilic carriers (mannitol, polyethylene glycol (PEG) 4000, PEG 6000, PEG 8000, and urea), surfactants (Tween-20, Tween-80, and sodium lauryl sulfate [SLS]) and cosolvents (ethanol, methanol, and glycerol) at 37°C. The solubility of valdecoxib could be enhanced significantly using PEG 4000 as a carrier, ethanol as cosolvent, and SLS as a surfactant. Because the solubility of valdecoxib increased dramatically in the presence of polyethylene glycols, these are suitable dispersing agents for preparing solid dispersions containing valdecoxib. Gibbs free energy (,G) values were all negative for all hydrophilic carriers tested, indicating the spontaneous nature of valdecoxib solubilisation. Among the cosolvents, ethanol exhibited higher solubilization potential than methanol and glycerol. As the dielectric constant of the cosolvent,water mixtures decreased, the solubility of valdecoxib increased. Finally, SLS exerted maximum solubilization of valdecoxib when compared to Tween-20 or Tween-80. The crystallinity of valdecoxib was explored by X-ray diffraction study and showed numerous crystalline peaks. Examination of surface morphology by scanning electron microscopy depicted a near spherical shape of valdecoxib with irregular surface characteristics. Drug Dev. Res. 62:41,48, 2004. © 2004 Wiley-Liss, Inc. [source]


    Synthesis, Structural, Thermal and Magnetic Characterization of a Pyrophosphato-Bridged Cobalt(II) Complex

    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 17 2008
    Oluwatayo F. Ikotun
    Abstract The reaction in water of CoII sulfate heptahydrate with 1,10-phenanthroline (phen) and sodium pyrophosphate (Na4P2O7) in a 2:4:1 stoichiometric ratio resulted in the crystallization of a neutral dinuclear CoII complex, {[Co(phen)2]2(,-P2O7)}·6MeOH (1), as revealed by a single-crystal X-ray diffraction study. The bridging pyrophosphato ligand between the two [Co(phen)2]2+ units in a bis(bidentate) coordination mode places the adjacent metal centers at 4.857 Å distance, and its conformation gives rise to intramolecular ,,, stacking interaction between adjacent phen ligands. Indeed, intermolecular ,,, stacking interactions between phen ligands from adjacent dinuclear complexes create a supramolecular 2D network in 1. Magnetic susceptibility measurements on a polycrystalline sample of 1 in the temperature range 1.9,295 K are typical of an overall antiferromagnetic coupling with a maximum of the magnetic susceptibility at 3.0 K. The analysis of the magnetic data in the whole temperature range allows the determination of the value of the intramolecular magnetic coupling (J = ,1.23 cm,1). The ability of the pyrophosphato ligand to mediate magnetic interactions between different first-row transition-metal ions when adopting the bis(bidentate) bridging mode is analyzed and discussed in the light of the small number of magneto-structural reports on this type of compound, bearing in mind the number of unpaired electrons and type of magnetic orbitals on each metal center. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]


    Breaking Infinite CuI Carboxylate Helix Held by Cuprophilicity into Discrete Cun Fragments (n = 6, 4, 2)

    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 2 2008
    Yulia Sevryugina
    Abstract A new copper(I) carboxylate complex with 3,5-bis(trifluoromethyl)benzoate ligands, [Cu(O2C(3,5-CF3)2C6H3)] (1), has been prepared in high yield and fully characterized. An X-ray diffraction study revealed a remarkable infinite double-helical chain motif held together by cuprophilic interactions ranging from 2.69 to 3.14 Å. Both left- and right-handed helices are present in the unit cell of the centrosymmetric structure of 1 thus making the crystalline compound racemic. Complex 1 shows bright emission at ca. 594 nm upon UV/Vis radiation in the solid state (,ex = 350 nm). The Cu···Cu contacts in 1 are easily broken in the gas phase to afford copper clusters of ascertained nuclearity upon sublimation with various polyaromatic hydrocarbons. Several polyarenes such as fluoranthene (C16H10), pyrene (C16H10), and coronene (C24H12) were selected to cover a broad temperature range from 130 to 220 °C for the gas-phase co-deposition reactions. As a result of the successive temperature increase, cleavage of the infinite copper(I) chain into [Cun(O2C(3,5-CF3)2C6H3)n] fragments of decreasing nuclearity, n = 6, 4, and 2, has been achieved. The isolation of these units represents the first instance where various polynuclear copper(I) complexes are prepared and structurally characterized for the same carboxylate ligand.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]


    New Molecular Charge-Transfer Salts of TM-TTF and BMDT-TTF with Thiocyanate and Selenocyanate Complex Anions [TMTTF = Tetramethyltetrathiafulvalene; BMDT-TTF = Bis(methylenedithio)tetrathiafulvalene]

    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 4 2003
    Marta Mas-Torrent
    Abstract Three new charge-transfer salts of tetrathiafulvalene (TTF)-based donors with thiocyanato- or selenocyanato-metal complex anions have been synthesised. The salts isolated were [BMDT-TTF]4[Cr(NCS)6] (1), [TM-TTF]4[Cr(NCS)6]·2CH3CN (2) and [TM-TTF]4[Cr(NCSe)6]·2CH3CN (3) [BMDT-TTF = bis(methylenedithio)tetrathiafulvalene and TM-TTF = tetramethyltetrathiafulvalene]. Single crystals of compound 1 crystallise in the monoclinic C2/c space group with a = 37.286(3), b = 10.0539(6), c = 21.069(2) Å, , = 124.348(4)°, V = 6520.9(9) Å3 and Z = 4. Compound 3 was also suitable for an X-ray diffraction study, however the anionic part, [Cr(NCSe)6], was highly disordered and the best solution gave a final R factor of 16.4%. A solution was found for the monoclinic space group C2/m with a = 13.787(3), b = 19.507(3), c = 14.735(5) Å, , = 102.90(3)°, V = 3862.9(17) Å3 and Z = 2. For compound 1 there are several S···S close atomic contacts between the donors and acceptors, but there is no discernible magnetic exchange between ions. Such an interaction was previously observed in related salts such as [TTF][Cr(NCS)4(phenanthroline)2] and [donor][M(NCS)4(isoquinoline)2] [M = Cr, Fe and donor = TTF, BEDT-TTF or TM-TTF (tetramethyltetrathiafulvalene)]. Compounds 1 to 3 are all paramagnetic semiconductors in which the magnetic susceptibility is dominated by the Cr-containing anions. The structure-function relationship, along with a comparison with related compounds, indicates that there is no long-range magnetic order because there are no ,-stacking interactions between donor and acceptor; these types of interactions are seen in all of the bulk magnets of this type in which the donor spin is magnetically coupled to the anion. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]


    Preparation, Crystallographic Characterization, and Theoretical Study of C70(CF3)14,

    EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 11 2006
    Alexey A. Goryunkov
    Abstract Five C70(CF3)14 isomers have been isolated chromatographically from the mixture produced in the ampoule reaction between C70 and CF3I at 390 °C. Molecular structures of four isomers have been determined in a single-crystal X-ray diffraction study. A quantum chemical survey of the theoretically possible isomers demonstrated that the structures obtained are energetically favorable but that there is probably no full thermodynamic control in the trifluoromethylation process.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]


    Diastereoselective Synthesis of New P-Stereogenic (ortho -Hydroxyaryl)diazaphospholidine,Borane Complexes by a Totally Stereoselective P,O to P,C Migration Rearrangement

    EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 6 2006
    Christian J. Ngono
    Abstract The totally diastereoselective synthesis of new P-stereogenic (o -hydroxyaryl)diazaphospholidines, in the form of their borane complexes 4a,4h, is described. The efficiency of this procedure is based both, on a one-pot and totally diastereoselective synthesis of the precursors (ortho -bromoaryloxy)diazaphosphospholidine,borane complexes 3a,3h, and on a stereoselective P,O to P,C migration rearrangement. A X-ray diffraction study of the structures of the product 4f and his precursor 3f shows unambiguously the totally stereoselectivity of the P,O to P,C rearrangement with clean retention of the phosphorus configuration.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]


    Synthesis and structural consideration of 1-chloro- N,N,,N,-tris(pentafluorophenyl)azagermatrane: Azagermatrane with the shortest intramolecular N , Ge bond

    HETEROATOM CHEMISTRY, Issue 7 2008
    El'mira Kh.
    Two compounds of a novel-type azagermatrane, N(CH2CH2NC6F5)3Ge-Hal: HalCl (1), Br (2), were prepared via a metathetical reaction of trilithium salt of tetramine, N[CH2CH2N(Li)C6F5]3, with corresponding GeHal4. A single crystal structure of 1 was determined by the X-ray diffraction study: The compound shows the strongest transannular Nax , Ge interaction (2.148(7) Å) among other studied azagermatranes. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:738,741, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20476 [source]


    Crystal structure of defect-containing semiconductor nanocrystals , an X-ray diffraction study

    JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 4 2009
    Maja Buljan
    Defects of crystal structure in semiconductor nanocrystals embedded in an amorphous matrix are studied by X-ray diffraction and a full-profile analysis of the diffraction curves based on the Debye formula. A new theoretical model is proposed, describing the diffraction from randomly distributed intrinsic and extrinsic stacking faults and twin blocks in the nanocrystals. The application of the model to full-profile analysis of experimental diffraction curves enables the determination of the concentrations of individual defect types in the nanocrystals. The method has been applied for the investigation of self-organized Ge nanocrystals in an SiO2 matrix, and the dependence of the structure quality of the nanocrystals on their deposition and annealing parameters was obtained. [source]


    Diffraction analysis of perovskite-like oxides containing irregular intergrowths

    JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2009
    L. Olikhovska
    Features of the X-ray intensity distributions caused by the presence of random and nonrandom stacking faults (irregular intergrowths) in layered perovskite-like oxides are studied by a computer simulation technique. It is shown that, apart from the stacking fault properties, the position, profile and intensity of a diffraction peak are dependent on the ratio between the c lattice parameter of the crystal and the thickness of the new structural fragment formed as a result of the stacking fault. A means of characterizing the stacking faults on the basis of the relative positions of pairs of diffraction peaks is presented. The approach is exemplified by the X-ray diffraction study of a disordered single crystal of the system Bi,Sr,Ca,Cu,O. [source]


    X-ray structure study of the light-induced metastable states of the spin-crossover compound [Fe(mtz)6](BF4)2

    JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2001
    Joachim Kusz
    Iron(II) complexes exhibiting thermal spin-crossover may be converted from the 1A1 low-spin (LS) state to the 5T2 high-spin (HS) state by irradiation with green light (light-induced excited spin-state trapping, LIESST) and from the LS to the HS state by irradiation with red light (reverse LIESST). The lifetime of the metastable LIESST states may be sufficiently long to enable an X-ray diffraction study. The lattice parameters of a single crystal of [Fe(mtz)6](BF4)2 (mtz = methyltetrazole) (space group P21/n) were measured between 300 and 10,K. While one Fe lattice site (A) of the crystal changes from the HS to the LS state near 78,K, the other site (B) remains in the LS state. Using the green light (514,nm) of an argon ion laser the crystal was quantitatively converted to the HS state at 10,K. Irradiation of the crystal at 10,K by red light of a laser diode (820,nm) with site A in the LS and site B in the HS state converts site B almost completely to the LS state. The lattice parameters of both metastable states were measured up to 50,K, where they start to decay on a minute timescale. At 10,K, a full data set for evaluation of the crystal structure was recorded. The volume change of the crystal per complex molecule accompanying the spin transition is 31.5,Å3 at site A and close to zero [,0.21,(14),Å3] at site B. [source]


    X-ray study of the light-induced metastable state of a spin-crossover compound

    JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2000
    Joachim Kusz
    Iron(II) complexes exhibiting thermal spin crossover may be converted from the 1A1 low-spin (LS) state to the 5T2 high-spin (HS) state by irradiation with green light (light-induced excited spin-state trapping, LIESST). The lifetime of the metastable LIESST state may be sufficiently long for X-ray diffraction study. The lattice parameters of a single crystal of [Fe(ptz)6](BF4)2 (ptz = propyltetrazole) were measured between 300 and 10,K, while the crystal changed from the HS to the LS state near 135,K. Using the green light (514,nm) of an argon-ion laser, the crystal was quantitatively converted to the metastable LIESST state at 10,K; its lattice parameters were measured up to 50,K, at which point the LIESST state begins to decay on a minute timescale. The change of the lattice parameters can be interpreted by a superposition of a normal temperature dependence, for which the isostructural zinc compound served as a reference, and an almost temperature-independent part which is proportional to the fraction of molecules in the HS state. [source]


    In situ micro-Raman and X-ray diffraction study of diamonds and petrology of the new ureilite UAE 001 from the United Arab Emirates

    METEORITICS & PLANETARY SCIENCE, Issue 7 2008
    Dominik C. HEZEL
    This is the first report of a meteorite in this country. The sample is heavily altered, of medium shock level, and has a total weight of 155 g. Bulk rock, olivine (Fo79.8,81.8) and pyroxene (En73.9,75.2, Fs15.5,16.9, Wo8.8,9.5) compositions are typical of ureilites. Olivine rims are reduced with Fo increasing up to Fo96.1,96.8. Metal in these rims is completely altered to Fehydroxide during terrestrial weathering. We studied diamond and graphite using micro-Raman and in situ synchrotron X-ray diffraction. The main diamond Raman band (LO = TO mode at ,1332 cm,1) is broadened when compared to well-ordered diamond single crystals. Full widths at half maximum (FWHM) values scatter around 7 cm,1. These values resemble FWHM values obtained from chemical vapor deposition (CVD) diamond. In situ XRD measurements show that diamonds have large grain sizes, up to >5 ,m. Some of the graphite measured is compressed graphite. We explore the possibilities of CVD versus impact shock origin of diamonds and conclude that a shock origin is much more plausible. The broadening of the Raman bands might be explained by prolonged shock pressure resulting in a transitional Raman signal between experimentally shock-produced and natural diamonds. [source]


    The local structure of ,-FeSi2 under high pressure

    PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2009
    Yoshihisa Mori
    Abstract We report the results of the high-pressure X-ray diffraction study and the high-pressure extended X-ray absorption fine structure study for ,-FeSi2 using the synchrotron radiation sources. The bond lengths of Fe,Fe, Si,Si, and Fe,Si under pressure were refined by the Rietveld method and the EXAFS analysis. It is interesting that the bond length of Si,Si is almost unchanged with increasing pressure. The DV-X, molecular orbital calculation was carried out for the crystal structure at 34.9 GPa and shows that the highest occupied molecular orbital consists of only 3d orbital of Fe atom. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    X-ray diffraction study of amorphous phase of BaSi2 under high pressure

    PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2007
    T. Nishii
    Abstract A high-pressure synchrotron X-ray diffraction study of zintl phase BaSi2 semiconductor has been performed up to 45 GPa. The pressure-induced amorphization occurred at 13 GPa. In the amorphous phase, the Ba,Si bond distance decreased with increasing pressure, while the Ba,Ba bond distances were almost unchanged. The Rietveld refinement revealed that these distances in the crystal phase decreased with increasing pressure. By combining these results, the Ba,Si bond compressibility in both phases is almost identical. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Energetic, Low-Melting Salts of Simple Heterocycles

    PROPELLANTS, EXPLOSIVES, PYROTECHNICS, Issue 4 2003
    Gregory Drake
    The synthesis of three new families of heterocyclic-based salts was undertaken and accomplished. Three triazole systems, 1H-1,2,4-triazole, 4-amino-1,2,4-triazole, and 1H-1,2,3-triazole, were used as proton bases with nitric (HNO3), perchloric (HClO4), and dinitramidic (HN(NO2)2) acid systems. In all cases, stable salts were recovered and fully characterized by vibrational spectra (IR, Raman), multinuclear NMR spectroscopy, material balance, density measurements, and elemental analyses, as well as DSC, TGA and initial safety testing (impact). Many of these salts have melting points well below 100,°C, yet high decomposition onsets, defining them as new, highly energetic members of the well known class of materials identified as ionic liquids. Additionally, the single crystal X-ray diffraction study of 1,2,4-triazolium perchlorate was investigated, revealing the expected structure. [source]


    X-ray diffraction by a crystal in a permanent external electric field: general considerations

    ACTA CRYSTALLOGRAPHICA SECTION A, Issue 4 2005
    Semen V. Gorfman
    The variations of X-ray diffraction intensities from a crystal in the presence of a permanent external electric field is modeled analytically using a first-order stationary perturbation theory. The change in a crystal, induced by an external electric field, is separated into two contributions. The first one is related to a pure polarization of an electron subsystem, while the second contribution can be reduced to the displacements of the rigid pseudoatoms from their equilibrium positions. It is shown that a change of the X-ray diffraction intensities mainly originates from the second contribution, while the influence of the pure polarization of a crystal electron subsystem is negligibly small. The quantities restored from an X-ray diffraction experiment in the presence of an external electric field were analyzed in detail in terms of a rigid pseudoatomic model of electron density and harmonic approximation for the atomic thermal motion. Explicit relationships are derived that link the properties of phonon spectra with E -field-induced variations of a structure factor, pseudoatomic displacements and piezoelectric strains. The displacements can be numerically estimated using a model of independent atomic motion if the Debye,Waller factors and pseudoatomic charges are known either from a previous single-crystal X-ray diffraction study or from density functional theory calculations. The above estimations can be used to develop an optimum strategy for a data collection that avoids the measurements of reflections insensitive to the electric-field-induced variations. [source]


    Incommensurate structure of Ca2Al2O5 at high temperatures , structure investigation and Raman spectroscopy

    ACTA CRYSTALLOGRAPHICA SECTION B, Issue 4 2008
    Biljana Lazic
    A high-temperature X-ray diffraction study revealed that brownmillerite-type Ca2Al2O5 transforms to an incommensurately modulated structure at elevated temperatures. Single crystals of Ca2Al2O5 were synthesized in an end-loaded piston cylinder press at 2.5,GPa and 1273,K. The diffraction pattern observed at 1090,(10),K by in situ single-crystal diffraction experiments can be indexed by an I -centred orthorhombic cell and a modulation wavevector of q = 0.595,(1)c*. A (3,+,1)-dimensional model in superspace group Imma(00,)s00 was used to refine the modulated structure. The structure is assembled from two building units: (i) layers of corner-sharing [AlO6] octahedra, stacked along b alternate with (ii) layers of zweier single chains of [AlO4] tetrahedra running along a. The modulated structure arises from an aperiodic sequence of two different configurations of the chains within the tetrahedral layers. The modulated high-temperature phase of Ca2Al2O5 is isotypic to the modulated high-temperature modification of Ca2Fe2O5. A large hysteresis was found in the phase-transition temperature. On heating, the transition occurs at ca 1075,(10),K; on cooling, satellite reflections can be observed down to 975,(10),K. The characterization of Ca2Al2O5 is completed by Raman spectroscopy, including a partial interpretation of the spectra. [source]


    Disordered misfit [Ca2CoO3][CoO2]1.62 structure revisited via a new intrinsic modulation

    ACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2008
    Hervé Muguerra
    The structure of the thermoelectric lamellar misfit cobalt oxide [Ca2CoO3][CoO2]1.62 was refined again using single-crystal X-ray diffraction data. A new commensurate intrinsic modulation was observed involving a modulation vector orthogonal to the misfit direction (,,0,,,). The five-dimensional superspace group is C2/m(1,0)(,0,)gm and the structure was solved using a commensurate approximation. A new model is given involving an occupation modulation of the split sites of the [CoO] layer. This [CoO] layer can be described by triple chains running along b. The residual disorder along b can then be explained by the assumption of a local ordering with two types of clusters: CoO2 and Co5O4. A powder neutron diffraction experiment confirmed the ordering evidenced by the single-crystal X-ray diffraction study, but was not sufficient by itself to deal with this double modulated scheme. The new intrinsic modulation is destroyed by partial metal substitutions in the [CoO] layer. The structural modifications of this layer directly influence the physical properties which are related to the electronic structure of the [CoO2] layers. [source]


    Structure and hydrogen bonding in 2,4-dihydroxybenzoic acid at 90, 100, 110 and 150,K; a theoretical and single-crystal X-ray diffraction study

    ACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2007
    Andrew Parkin
    A new polymorph of 2,4-dihydroxybenzoic acid is reported. The structure was characterized by multiple-temperature X-ray diffraction and solid-state DFT computations. The material shows a geometric pattern of hydrogen bonding consistent with cooperativity between the intermolecular carboxylic acid dimer and intramolecular hydrogen bonds. The presence of proton disorder within this hydrogen-bond system, which would support such a cooperative model, was not fully ruled out by the initial X-ray studies. However, solid-state calculations on the three possible end-point tautomers indicate that the dominant crystallographically observed configuration is substantially lower in energy than the other tautomers (by at least 9,kJ,mol,1), indicating that no disorder should be expected. It is therefore concluded that no disorder is observed either in the intra- or intermolecular hydrogen bonds of the title compound and that the cooperativity between the hydrogen bonds is not present within the temperature range studied. [source]


    An X-ray diffraction study of partially ordered electron density in clathrates of Dianin's compound that include simple carboxylic acids

    ACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2003
    Ronald W. H. Small
    The nature of the inclusions in ten clathrate complexes of Dianin's compound have been investigated by the use of electron-density difference maps. The guest species are the first eight straight-chain carboxylic acids, formic to octanoic, a branched-chain acid (dimethylacetic acid) and trifluoroacetic acid. The point-group symmetry of the clathrate cavity, , is satisfied by partial occupation of symmetry-related sites by two included molecules in the case of formic, acetic and trifluoroacetic acids and by a single molecule in the remainder. Hydrogen-bonding requirements in the case of formic and acetic acids are satisfied by dimer formation; in the trifluoroacetic acid complex the two acid molecules form hydrogen bonds to framework O atoms at either end of the cavity. The adoption of gauche conformations in heptanoic and octanoic acid chains shortens them sufficiently that they fit the cavity with only slight distortion. [source]


    X-ray diffraction study of the phase transition of K2Mn2(BeF4)3: a new type of low-temperature structure for langbeinites

    ACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2001
    A. Guelylah
    The potassium manganese tetrafluoroberyllate langbeinite compound has been studied in the temperature range 100,300,K. Using DSC measurements, a phase transition has been detected at 213,K. The space group of the low-temperature phase was determined to be P1121 using X-ray diffraction experiments and optical observations of the domain structure. The b axis is doubled with respect to the prototypic P213 cubic phase. Lattice parameters were determined by powder diffraction data [a = 10.0690,(8), b = 20.136,(2), c = 10.0329,(4),Å, , = 90.01,(1)°]. A precise analysis of the BeF4 tetrahedra in the low-temperature phase shows that two independent tetrahedra rotate in opposite directions along the doubled crystallographic axis. A symmetry mode analysis of the monoclinic distortion is also reported. This is the first report of the existence of such a phase transition in K2Mn2(BeF4)3 and also of a new type of low-temperature structure for langbeinite compounds. [source]


    Apparent shortening of the Csp3,Csp3 bond analysed via a variable-temperature X-ray diffraction study in racemic 1,1,-binaphthalene-2,2,-diyl diethyl bis(carbonate)

    ACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2009
    Susanta K. Nayak
    Crystal structure determination at room temperature [292,(2),K] of racemic 1,1,-binaphthalene-2,2,-diyl diethyl bis(carbonate), C26H22O6, showed that one of the terminal carbon,carbon bond lengths is very short [Csp3,Csp3 = 1.327,(6),Å]. The reason for such a short bond length has been analysed by collecting data sets on the same crystal at 393, 150 and 90,K. The values of the corrected bond lengths clearly suggest that the shortening is mainly due to positional disorder at two sites, with minor perturbations arising as a result of thermal vibrations. The positional disorder has been resolved in the analysis of the 90,K data following the changes in the unit-cell parameters for the data sets at 150 and 90,K, which appear to be an artifact of a near centre of symmetry relationship between the two independent molecules in the space group P at these temperatures. Indeed, the unit cell at low temperature (150 and 90,K) is a supercell of the room-temperature unit cell. [source]


    Synthesis of a new salphen-type titanium complex and its application in ethylene polymerization and copolymerization

    APPLIED ORGANOMETALLIC CHEMISTRY, Issue 7 2010
    Xiaojing Wen
    Abstract TiCl2[salphen(di- tBu)] was synthesized, characterized and employed as pre-catalyst in ethylene homo- and copolymerization with propylene, 1-octene and 10-undecen-1-ol. X-ray diffraction study on the titanium complex revealed a distorted octahedral coordination of the central metal with a trans -Cl, cis -O, cis -N arrangement. The complex combined with MAO afforded moderate catalytic activities in ethylene polymerization. Furthermore the catalyst not only copolymerized ethylene with apolar monomer (propylene and 1-octene), but also possessed significant capability of incorporation with polar monomer (10-undecen-1-ol). Only single insertion of 1-octene unit in ethylene- co -1-octene polymer was detected by 13C NMR spectrum. Copyright © 2010 John Wiley & Sons, Ltd. [source]


    Germanium carboxylates: the first X-ray diffraction study of germanium(II) dicarboxylate and germanium(IV) tetracarboxylate

    APPLIED ORGANOMETALLIC CHEMISTRY, Issue 6 2005
    Victor N. Khrustalev
    Abstract Germanium(II) dipropionate (1) has been synthesized and its crystal structure, as well as that of germanium(IV) tetrapropionate (2), has been determined. By contrast to monomeric 2 with monodentate propionate ligands, compound 1 is associated, forming a cyclotetramer [Ge(O2CEt)2]4 (1a) via intermolecular dative CO , Ge interactions. Copyright © 2005 John Wiley & Sons, Ltd. [source]