The structure and dynamics of compounds related to fast ionic conductors

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The crystal-structures of (NH4)(3)HGE7016-center-dot-NH(2)O and Li4-xhxge7016-center-dot-NH(2)0 determined from powder diffraction data using synchrotron-radiation

The structures of two hydrated microporous germanates (NH4)(3)HGe7O16. nH(2)O and Li4-xHxGe7O16. nH(2)O [n = 2.72(3) and 5.61(5), respectively], have been determined in space group P(4) over bar3$ m, Z = 1, with a = 7.71069(1) Angstrom and 7.71936(1) Angstrom respectively, from Rietveld refinement of powder diffraction patterns collected using synchrotron radiation. The profiles contain 119 and 104 reflections, respectively. The structure of these germanates consists of a three-dimensional framework with charge compensating cations and water molecules occupying the interconnecting channels. The ammonium cations occupy sites near the centre of a 3.3 Angstrom window and form a disordered hydrogen-bonded network with the water molecules. This is presumably responsible for the ionic conductivity observed in this material

A structural investigation of the four phases of 7-oxabicyclo[2.2.1]heptane

Powder synchrotron X-ray diffraction studies confirm that 7-oxabicyclo[2.2.1]heptane, (oxanorbornane), forms three solid phases on cooling and four on warming, as previously indicated by spectroscopic and DSC meas urements. The two highest temperature phases are orien tationally disordered with phase I being face-centred cubic (a = 8.5469(1) Å at 240 K) and phase II primitive cubic (a = 10.60558(4) Å at 194 K). Phase III, which appears over a narrow temperature range on warming, is monoclinic, space group P21/a, Z' = 4, with a = 21.858(4) Å, b = 10.964(2) Å, c = 9.333(1) Å β = 90.491(8)° at 185 K. Phase IV, which occurs below 175 K, is monoclinic, space group C2/c, Z' = 3, with a = 13.6372(2) Å, b = 10.2593(1) Å, c = 24.0466(3) Å, β = 102.5212(4)° at 50 K. The structures of phases III and IV are ordered and have been solved from the powder diffraction data by direct-space methods, then refined by the Rietveld method, restraining the molecules to the known structure, which has m2m (C2v) symmetry

The low-temperature structure of nopinone

6,6-dimethylbicyclo[3.1.1]heptan-2-one, (1R)-(+)-nopinone, is a liquid at room temperature. It solidifies below 260 K to form an orientationally disordered body-centred cubic phase (a = 7.644 Å at 255 K), which transforms to an ordered structure below 240 K. The low-temperature structure has been solved from powder X-ray diffraction data, and is orthorhombic, space group P212121, Z' = 1, Z = 4, with a = 17.6441(8) Å, b = 6.9682(3) Å, c = 6.5272(3) Å at 120 K

βCO-(ET)2I3 : Crystallographic evidence for the co-existence of ordered β*-(ET)2I3 (TC ≈ 8 K) and disordered β-(ET)2I3 (TC ≈ 2 K)

The crystal structures of microcrystalline βCO-(ET)2I3 were determined at temperatures of 293, 200, 130, 100, and 35 K from X-ray single crystal diffraction data employing synchrotron radiation. The structure of βCO-(ET)2I3 at 293 K is similar to that of the known superconductor β-(ET)2I3 (Tc = 1.4 – 2 K). By contrast to β-(ET)2I3, the title compound was found to be slightly iodine-deficient and is better described by the formula βCO-(ET)2I3-x (x = 0.014). At 293 K, one ethylene group of the ET cations is disordered with the eclipsed conformation prevailing over the staggered conformer, while at 200 K the occupancies of both arrangements are equal. Upon cooling to 130 K and below, about 60% of the ethylene groups adopt a staggered conformation, thus providing clear-cut evidence for a temperature-induced, partial ordering process. Ac susceptibility measurements show a Tc-onset at 8 K followed by a broad transition and a second superconducting transition at around 2 K. The observation of both partial end group ordering and twofold superconducting transition is interpreted as co-existence of ordered β*-(ET)2I3 (TC ≈ 8 K) and disordered β-(ET)2I3 TC= 1.4 - 1.8 K) in the title compound

Crystal and molecular structures of 2-[1-(2-aminoethyl)-2-imidazolidinylidene]-2-nitro-acetonitrile (C7H11N5O2) and2,6-dianlino-5-hydroxy-3-nitro4H-pyrazolo[1,5-a]-pyrimidin-7-one monohydrate (C6H6N6O4 center dot H2O) from X-ray, synchroton and neutron powder diffraction data.

The crystal and molecular structures of 2-[1-(2-aminoethyl)-2-imidazolidinylidene]-2-nitroacetonitrile [C7H11N5O2; space group P21/n; Z = 4; a = 7.4889 (8), b = 17.273 (2), c = 7.4073 (8) Å, β = 111.937 (6)°], (I), and 2,6-diamino-5-hydroxy-3-nitro-4H-pyrazolo[1,5-a]pyrimidin-7-one monohydrate [C6H6N6O4·H2O; space group P21/n; Z = 4; a = 17.576 (3), b = 10.900 (2), c = 4.6738 (6) Å, β = 92.867 (8)°], (II), have been determined from X-ray, synchrotron and neutron powder diffraction data using various methods. The structures were originally solved from Guinier photographs with a grid search procedure and the program MRIA using a priori information from NMR and mass spectra on the possible geometry of the molecules. Because the conformation of molecule (I) changed during the bond-restrained Rietveld refinement, solvent water was found in (II) and, moreover, as both Guinier patterns were corrupted by texture, high-resolution texture-free synchrotron data were collected at the BM16 beamline, ESRF, to confirm the original results. Using the set of |F| 2 values derived from the synchrotron patterns after full-pattern decomposition procedures, the structures of (I) and (II) were solved by direct methods via SHELXS96, SIRPOW.92 and POWSIM without any preliminary models of the molecules, and by Patterson search methods via DIRDIF96 and PATSEE with the use of rigid fragments from each of the molecules. The neutron patterns allowed (I) and (II) to be solved using the grid search procedure and correct initial models of the molecules including H atoms. The results obtained from powder patterns measured on different devices demonstrate the high level of reproducibility and reliability of various powder software and equipment, with a certain preference for synchrotron facilities.</jats:p