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Synchrotron X-ray Powder Diffraction Data (synchrotron + x-ray_powder_diffraction_data)
Selected AbstractsObservation of orientational disorder in the hexagonal stuffed tridymite Sr0.864Eu0.136Al2O4 by the maximum-entropy methodJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 5 2004H. Yamada The crystal structure of a strontium europium aluminate, Sr0.864Eu0.136Al2O4, with a novel hexagonal form was investigated by a combination of Rietveld analysis and the maximum-entropy method (MEM) with synchrotron X-ray powder diffraction data. The electron density image calculated by the MEM/Rietveld method revealed that the apical oxygen ion in the AlO4 tetrahedron has a broad distribution corresponding to an extraordinarily large atomic displacement parameter. This structure could be expressed by a split-atom model, with which the Rietveld refinement gave Rwp = 2.99% and RB = 4.16%. Subsequently, MEM-based pattern fitting (MPF) decreased the R factors to Rwp = 2.81% and RB = 2.34% and the electron density image clearly showed that the apical oxygen ions of the AlO4 tetrahedra are split over three sites around a threefold axis involving an elongated distribution of the residual O ions along the c axis. These results suggest that AlO4 tetrahedra in Sr0.864Eu0.136Al2O4 are orientationally disordered. [source] Characterization and crystal structure of D -mannitol hemihydrateJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 11 2004Cletus Nunes Abstract The objectives of this study were (i) to isolate and characterize mannitol hydrate, and (ii) to solve its crystal structure from high-resolution synchrotron X-ray powder diffraction data. Mannitol hydrate was prepared by freeze-drying aqueous mannitol solutions (5% w/v) under controlled conditions. X-ray powder diffractometry, differential scanning calorimetry, and thermogravimetric analyses indicated that mannitol exists as a hemihydrate (C6H14O6,·,0.5H2O). Synchrotron data were collected on the X3B1 beamline at the National Synchrotron Light Source. The simulated annealing program PSSP was used to solve the structure, which was subsequently refined by Rietveld analysis using the program package GSAS. The compound crystallizes in space group P1, with a,=,9.8963 Å, b,=,10.5424 Å, c,=,4.7860 Å, ,,=,102.589°, ,,=,86.092°, and ,,=,116.079°. The unit cell contains two dissimilar D -mannitol molecules and one water molecule, forming a hydrogen bonding pattern significantly different from that seen in the anhydrous polymorphs. © 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 93:2800,2809, 2004 [source] Molecular and crystalline structures of three (S)-4-alkoxycarbonyl-2-azetidinones containing long alkyl side chains from synchrotron X-ray powder diffraction dataACTA CRYSTALLOGRAPHICA SECTION B, Issue 6 2009Luis E. Seijas The (S)-4-alkoxo-2-azetidinecarboxylic acids are optically active ,-lactam derivatives of aspartic acid, which are used as precursors of carbapenem-type antibiotics and poly-,-aspartates. The crystal structures of three (S)-4-alkoxo-2-azetidinecarboxylic acids with alkyl chains with 10, 12 and 16 C atoms were solved using parallel tempering and refined against the X-ray powder diffraction data using the Rietveld method. The azetidinone rings in the three compounds display a pattern of asymmetrical bond distances and an almost planar conformation; these characteristics are compared with periodic solid-state, gas-phase density-functional theory (DFT) calculations and MOGUL average bond distances and angles from the CSD. The compounds pack along [001] as corrugated sheets separated by approximately 4.40,Å and connected by hydrogen bonds of the type N,H...O. [source] Structures of strontium diformate and strontium fumarate.ACTA CRYSTALLOGRAPHICA SECTION B, Issue 4 2009A synchrotron powder diffraction study The crystal structures of strontium diformate in space groups P212121 (, form, 295,K), P41212 (, form, 334 and 540,K) and I41/amd (, form, 605,K), and strontium fumarate in space groups Fddd (, form, 105,K) and I41/amd (, form, 293,K) have been determined from synchrotron X-ray powder diffraction data. Except for the ,-strontium diformate, all the structures are based on a diamond-like Sr-ion arrangement, as in strontium acetylene dicarboxylate. The formate ions are disordered in the , phase owing to steric hindrance. The fumarate ions are disordered over four (,) or two (,) symmetry-equivalent orientations. ,-Strontium fumarate crystallizes with a unique 90° carboxylate dihedral angle, and is stable up to 773,K. [source] The Stuffed Framework Structure of SrP2N4: Challenges to Synthesis and Crystal Structure DeterminationCHEMISTRY - A EUROPEAN JOURNAL, Issue 24 2007Friedrich 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] | ||||||||||