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Synchrotron Powder Diffraction Data (synchrotron + powder_diffraction_data)

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Chemistry	100%

Selected Abstracts

High-Spin- and Low-Spin-State Structures of [Fe(chloroethyltetrazole)6](ClO4)2 from Synchrotron Powder Diffraction Data

CHEMISTRY - A EUROPEAN JOURNAL, Issue 19 2006
Eva Dova Dr.
Abstract The spin-crossover complex [Fe(teec)6](ClO4)2 (teec = chloroethyltetrazole) exhibits a 50,% incomplete spin crossover in the temperature range 300,30 K. Time-resolved synchrotron powder diffraction experiments have been carried out to elucidate its structural behavior. We report crystal structure models of this material at 300 K (high spin) and 90 K (low spin), as solved from synchrotron powder diffraction data by using Genetic Algorithm and Parallel Tempering techniques and refined with Rietveld refinement. During short synchrotron powder diffraction experiments (five minutes duration) two distinguishable lattices were observed the quantities of which vary with temperature. The implication of this phenomenon, that is interpreted as a structural phase transition associated with the high-to-low spin crossover, and the structural characteristics of the high-spin and low-spin models are discussed in relation to other compounds showing a similar type of spin-crossover behavior. [source]

Orientational ordering, tilting and lone-pair activity in the perovskite methylammonium tin bromide, CH3NH3SnBr3

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 4 2010
Ian Swainson
Synchrotron powder diffraction data from methylammonium tin bromide, CH3NH3SnBr3, taken as a function of temperature, reveal the existence of a phase between 230 and 188,K crystallizing in Pmc21, a = 5.8941,(2), b = 8.3862,(2), c = 8.2406,(2),Å. Strong ferroelectric distortions of the octahedra, associated with stereochemical activity of the Sn 5s2 lone pair, are evident. A group analysis and decomposition of the distortion modes of the inorganic framework with respect to the cubic parent is given. The primary order parameters driving this upper transition appear to be an in-phase tilt (rotation) of the octahedra coupled to a ferroelectric mode. The precise nature of the lower-temperature phase remains uncertain, although it appears likely to be triclinic. Density-functional theory calculations on such a triclinic cell suggest that directional bonding of the amine group to the halide cage is coupled to the stereochemical activity of the Sn lone pair via the Br atoms, i.e. that the bonding from the organic component may have a strong effect on the inorganic sublattice (principally via switching the direction of the lone pair with little to no energy cost). [source]

A differential thermal expansion approach to crystal structure determination from powder diffraction data

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2008
P. Fernandes
Differential thermal expansion over the range 90,210,K has been applied successfully to determine the crystal structure of chlorothiazide from synchrotron powder diffraction data using direct methods. Key to the success of the approach is the use of a multi-data-set Pawley refinement to extract a set of reflection intensities that is more `single-crystal-like' than those extracted from a single data set. The improvement in reflection intensity estimates is quantified by comparison with reference single-crystal intensities. [source]

Chlorartinite, a volcanic exhalation product also found in industrial magnesia screed

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 5 2006
Kunihisa Sugimoto
The volcanic exhalation product chlorartinite, [Mg2(CO3)(H2O)(OH)]Cl·H2O, has recently been found to be a minor, and in some samples a major, component of magnesia floors for industrial use. In order to be able to perform quantitative phase analysis using the Rietveld method, its crystal structure was determined from high-resolution synchrotron powder diffraction data by the global optimization technique of simulated annealing and Rietveld refinement. The final Rp and Rwp values are 5.23% and 6.56%, respectively. Chlorartinite crystallizes in the rhombohedral space group R3c (No. 161), with a = 23.14422,(16),Å, c = 7.22333,(5),Å, V = 3350.84,(5),Å3, Z = 18. The building units of chlorartinite consist of MgO6 octahedra forming 15-membered puckered rings which are interconnected by CO3 triangular moieties. The rings are stacked to form a honeycomb-like three-dimensional framework structure with large isolated channels. Within the channels, free chlorine atoms and disordered water molecules are located. [source]

Multipole electron-density modelling of synchrotron powder diffraction data: the case of diamond

ACTA CRYSTALLOGRAPHICA SECTION A, Issue 4 2010
H. Svendsen
Accurate structure factors are extracted from synchrotron powder diffraction data measured on crystalline diamond based on a novel multipole model division of overlapping reflection intensities. The approach limits the spherical-atom bias in structure factors extracted from overlapping powder data using conventional spherical-atom Rietveld refinement. The structure factors are subsequently used for multipole electron-density modelling, and both the structure factors and the derived density are compared with results from ab initio theoretical calculations. Overall, excellent agreement is obtained between experiment and theory, and the study therefore demonstrates that synchrotron powder diffraction can indeed provide accurate structure-factor values based on data measured in minutes with limited sample preparation. Thus, potential systematic errors such as extinction and twinning commonly encountered in single-crystal studies of small-unit-cell inorganic structures can be overcome with synchrotron powder diffraction. It is shown that the standard Hansen,Coppens multipole model is not flexible enough to fit the static theoretical structure factors, whereas fitting of thermally smeared structure factors has much lower residuals. If thermally smeared structure factors (experimental or theoretical) are fitted with a slightly wrong radial model (s2p2 instead of sp3) the radial scaling parameters (`,' parameters) are found to be inadequate and the `error' is absorbed into the atomic displacement parameter. This directly exposes a correlation between electron density and thermal parameters even for a light atom such as carbon, and it also underlines that in organic systems proper deconvolution of thermal motion is important for obtaining correct static electron densities. [source]

Structure of pyrrhotite 5C (Fe9S10)

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2010
Alexander Dean Elliot
The distribution of vacancies throughout the underlying NiAs structure of pyrrhotite 5C was analysed through the application of vacancy avoidance and the closeness condition in conjunction with order,disorder layering. Two crystallographically equivalent structure solutions (chiral enantiomers) were produced consisting of layers containing one vacancy in every eight iron sites broken by a fully occupied layer every fifth iron layer, and best described by monoclinic statistical models. The statistical 5C structures were verified using synchrotron powder diffraction data as well as published electron-diffraction patterns. An order,disorder structure description is proposed for the intermediate pyrrhotites of which pyrrhotite 5C is an end-member. [source]

Structure solution of the new titanate Li4Ti8Ni3O21 using precession electron diffraction

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2010
Mauro Gemmi
A sample having stoichiometry Li[Ti1.5Ni0.5]O4 has been synthesized to obtain a spinel structure. The resulting crystalline powder revealed a multiphase nature with spinel as the minor phase. The main phase is a new trigonal phase having a = 5.05910,(1), c = 32.5371,(1),Å. The structure has been solved by direct methods working on a three-dimensional set of intensities obtained from a precession electron-diffraction experiment, and refined on synchrotron powder diffraction data in the space group . The model consists of hexagonal layers of edge-sharing octahedra occupied either by the heavy cations Ti and Ni, or preferentially by Li. On the basis of cation-site occupancies the stoichiometry becomes Li4Ti8Ni3O21, which is compatible with the microanalysis results. [source]

SiBr4, prediction and determination of crystal structures

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2009
Alexandra K. Wolf
For SiBr4 no crystal structures have been reported yet. In this work the crystal structures of SiBr4 were predicted by global lattice-energy minimizations using force-field methods. Over an energy range of 5,kJ,mol,1 above the global minimum ten possible structures were found. Two of these structures were experimentally determined from X-ray synchrotron powder diffraction data: The low-temperature , phase crystallizes in P21/c, the high-temperature , phase in . Temperature-dependant X-ray powder diffraction shows that the phase transition occurs at 168,K. [source]

Structure of lithium benzilate hemihydrate solved by simulated annealing and difference Fourier synthesis from powder data

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2003
Asiloé J. Mora
The crystal structure of lithium benzilate hemihydrate (C14H11OLi+·0.5H2O) was solved from synchrotron powder diffraction data. This compound crystallizes in the monoclinic space group P21/a. The structure was solved via the direct space search for two benzilate fragments using the simulated-annealing program DASH, localization of the lithium ions and water molecule from a difference Fourier map, and a restrained Rietveld refinement (Rwp = 0.0687). The structure is a coordination polymer of [Li2(C14H11O3)2·H2O]2 tetramers building helical fourfold one-dimensional channels parallel to [010]. Inside the channels the tetrahedral coordination spheres of the lithium ions contain hydroxyl and carbonyl groups, and water molecules. The water molecule functions as the cohesive entity forming extended hydrogen-bonded chains running along [010], and bifurcated donor hydrogen bonds with the two nearest carboxylates. At the outer edge of the channels, weaker intermolecular C,H,Ph hydrogen bonds along [100] and [001] contribute to the supramolecular aggregation of the structure. [source]

The Stuffed Framework Structure of SrP2N4: Challenges to Synthesis and Crystal Structure Determination

CHEMISTRY - A EUROPEAN JOURNAL, Issue 24 2007
Friedrich
Abstract SrP2N4 was obtained by high-pressure high-temperature synthesis utilizing the multianvil technique (5,GPa, 1400,°C) starting from mixtures of phosphorus(V) nitride and strontium azide. SrP2N4 turned out to be isotypic with BaGa2O4 and is closely related to KGeAlO4. The crystal structure (SrP2N4, a=17.1029(8), c=8.10318(5),Å, space group P63 (no. 173), V=2052.70(2),Å3, Z=24, R(F2)=0.0633) was solved from synchrotron powder diffraction data by applying a combination of direct methods, Patterson syntheses, and difference Fourier maps adding the unit cell information derived from electron diffraction and symmetry information obtained from 31P solid-state NMR spectroscopy. The structure of SrP2N4 was refined by the Rietveld method by utilizing both neutron and synchrotron X-ray powder diffraction data, and has been corroborated additionally by 31P solid-state NMR spectroscopy by employing through-bond connectivities and distance relations. [source]