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  • 1
    Electronic Resource
    Electronic Resource
    Structures of Fluoroarsenates KAsF6n(OH)n, n = 0, 1, 2: Application of the Heavy-Atom Method for Modulated Structures (1998)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 54 (1998), S. 809-818 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Structures of KAsF6−n(OH)n, n = 0, 1, 2, have been determined from single-crystal X-ray diffraction data. Potassium hexafluoroarsenate, KAsF6, has a standard structure, potassium hydroxopentafluoroarsenate, KAsF5(OH), has a superstructure, and potassium dihydroxotetrafluoroarsenate, KAsF4(OH)2, has an incommensurate modulated structure. The superstructure has been solved both in the supercell by standard methods and in the basic cell as a commensurate modulated structure, giving the same results in both cases. The heavy-atom method for modulated structures has been developed and applied to identify a good starting point for the refinement of strongly modulated KAsF4(OH)2. Moreover, the influence of hydrogen bonding on a regular disturbance of simple translation symmetry of the structure is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108768198006351
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  • 2
    Electronic Resource
    Electronic Resource
    Determination of the modulated structure of Sr14/11CoO3 through a (3 + 1)-dimensional space description and using non-harmonic ADPs (1999)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 55 (1999), S. 841-848 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Sr14/11CoO3 (i.e. Sr14Co11O33, tetradecastrontium undecacobalt tritriacontaoxide), a new phase in the hexagonal perovskite SrxCoO3 system, has been prepared and its structure solved from single-crystal X-ray data within the (3 + 1)-dimensional formalism. Sr14/11CoO3 crystallizes in the trigonal symmetry, R3¯m(00γ)0s superspace group with the following lattice parameters: as = 9.508 (2), cs = 2.5343 (7) Å, q = 0.63646 (11)c* and Vs = 198.40 (13) Å3. With the commensurate versus incommensurate test not being conclusive, the structure was considered as commensurate (P32 three-dimensional space group), but refined within the (3 + 1)-dimensional formalism to a residual factor R = 0.0351 for 47 parameters and 1169 independent reflections. Crenel functions were used for the oxygen and cobalt description and a Gram–Charlier expansion up to the third order of the atomic displacement parameter was employed for one Co atom. The structure is similar to that of Sr6/5CoO3, but with a different sequence of the octahedra and trigonal prism polyhedra along the [CoO3] chains. An interesting feature evidenced by the non-harmonic expansion is the displacement of the prismatic Co atoms from the site center, towards the prism rectangular faces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108768199006485
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  • 3
    Electronic Resource
    Electronic Resource
    Refinement of modulated structures against X-ray powder diffraction data with JANA2000 (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 398-404 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: JANA is a computer program for the refinement and analysis of periodic and aperiodic (incommensurately modulated structures and composite crystals) crystal structures. Here a new module is introduced that allows Rietveld refinements against powder diffraction data. It is shown that JANA2000 provides a state-of-the-art description of the peak profiles. A re-analysis of the low-temperature structure of (CO)xC60 showed that the application of icosahedral symmetry restrictions to the C60 molecule leads to a better description of the electron density and to a corrected position of the CO molecule as compared with a rigid-body refinement. The incommensurately modulated structure of NbTe4 has been successfully refined against X-ray powder diffraction data. The structural parameters are equal to, but less accurate, than the parameters obtained from a single-crystal study.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889801003302
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  • 4
    Electronic Resource
    Electronic Resource
    Hexamethylenetetramine Sebacate, an Incommensurate Structure with Large Nonsinusoidal Modulations: Comparison of Two Refinement Strategies (1998)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 54 (1998), S. 31-43 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The organic salt hexamethylenetetramine sebacate presents a 1D modulation with strong satellite reflections. Single-crystal X-ray intensities of main reflections and satellites up to sixth order have been measured at room temperature and used to refine this incommensurate structure. Two incommensurate structure models of hexamethylenetetramine (hexamine) sebacate are proposed and compared. The first is based on displacive atomic modulation functions and the second one uses displacive modulation and occupational step functions. Both models require high-order harmonic terms to describe the strongly nonsinusoidal modulation components. The structural characteristics of hexamine sebacate are similar in the two models. The structure is a layer structure consisting of alternating sheets of hexamine and sebacic acid connected by H bonds. Each layer of sebacic acid molecules consists of close-packed aliphatic chains with their axis slightly tilted with respect to the layer normal. The chains form alternating areas, each of which is characterized by a common orientation of the chains. These characteristics have also been observed in hexamethylenetetramine suberate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767397010295
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  • 5
    Electronic Resource
    Electronic Resource
    Crystal data for an adduct of orthotelluric acid and urea, Te(OH)6.2CO(NH2)2 (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 202-202 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The crystal data of the title compound have been determined from single-crystal data [Loub, Haase & Mergehenn (1979). Acta Cryst. B35, 3039–3041]: C2/c, a = 14.828(8), b = 8.891(6), c = 10.023(7) Å, β = 129.13(3)°, V = 1025.0(9) Å3, Z = 4, Dm = 2.31(3), Dx = 2.27 Mg m−3. Power data obtained with powder diffractometer, θ–2θ scan, T = 295 K, Cu Kα radiation are presented. Infrared and Raman spectra are given. Thermal decomposition is reported [Fábry, Loub & Feltl (1982). J. Therm. Anal. 24, 95–100]. The JCPDS Diffraction File No. for C2H8N4O2Te(OH)6 is 36-1470.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889886089628
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  • 6
    Electronic Resource
    Electronic Resource
    Structure of μ-(tetraphthalato)-bis[N,N'-ethylenebis(salicylaldiminato)iron(III)] (1992)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 48 (1992), S. 1579-1582 
    Details
    ISSN: 1600-5759
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108270192000982
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