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Redetermination of the Structure of K2SnBr6 at room temperatureRao, S. 08 1900 (has links)
<p> The crystal structure of k2SnBr6 has been reinvestigated using single crystal x-ray diffraction techniques. Three dimensional intensity data obtained photographically have been used to refine the structure, by the least square analysis. The structure is found to be slightly distorted from the regular cubic k2PtCl6 structure in a manner similar to K2TeBr6. The Sn-Br bond is found to be 2.601 A. </p> <p> The structure of k2SnBr6 is found to be monoclinic with space group P21/n and a = 7.435 ± 0.017 A, b= 7.437 ± 0.017 A, and c = 10.568 ± 0.006 A. </p> <p> A review of other crystals with similar structure is included in this thesis included the theory of x-ray diffraction and crystal structure as applicable to the present problem is discussed briefly. </p> / Thesis / Master of Science (MSc)
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Crystal Structure of SilaneSears, William Maxwell 02 1900 (has links)
<p> The lattice parameters and crystal symmetry of silane (SiH4) are examined by X-ray powder diffraction. Comparisons are made with vibrational spectrum and birefringence
measurements and with respect to an order-disorder transition between the two solid phases of silane.</p> / Thesis / Master of Science (MSc)
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Predicting the crystal structure of organic molecular materialsChaka, Anne Marie January 1993 (has links)
No description available.
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Structural Studies of Escherichia coli RecE ExonucleaseZhang, Jinjin January 2009 (has links)
No description available.
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X-ray crystallographic structure of the potent antiplasmodial compound 2,7-dibromocryptolepine acetic acid solvate.Potter, B.S., Lisgarten, J.N., Pitts, J.E., Palmer, R.A., Wright, Colin W. January 2008 (has links)
No / The structure of 2,7-dibromocryptolepine acetic
acid solvate, C16H11N2Br2 [1.5(C2H4O2)][C2H3O2
-]
[0.5H2O], Mr = 460.17, has been determined from X-ray
diffraction data. The crystals are monoclinic, space group
P21/c with Z = 4 molecules per unit cell and a =
7.3243(3), b = 18.7804(6), c = 15.8306(7) A ° , b = 94.279(1) ,
Vc = 2171.5(2) A ° , crystal density Dc = 1.667 g/cm3. The
structure was determined using direct methods and refined
by full-matrix least-squares to a conventional R-index of
0.0496 for 4,908 reflections and 258 parameters. The cryptolepine
nucleus of the 2,7-dibromocryptolepine molecule
is highly planar and the two Br atoms are in this plane
within 0.06 and 0.01 A ° , respectively. The crystal structure
is maintained via hydrogen bonding between N(10) in the
cryptolepine nucleus and the oxygen of one of the three
solvated acetic acid molecules. The acetic acid molecules
also form hydrogen bonded chains. Acetic acid B is
deprotonated and its two C¿O bond lengths are equivalent,
unlike those in A and C. Acetic acid C lies very close to a
crystallographic centre of symmetry. To avoid overlap the
two repeats cannot exist together and are subject to 50%
statistical disorder. O(1C) of this methanol is furthest from
the two-fold axis and its occupancy refines to a value of 1.0
and is assumed to exist alternately as a water oxygen
hydrogen bonding to methanol O(1C) across the two-fold
axis at a distance of 2.775 A ° .
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Low Temperature X-Ray Crystallographic Structure of the Antiplasmodial Compound 5-N-Hydroxyethanequindoline Hydrochloride 0.5CH3OH.Hampson, Hannah C., Ho, Chung Y., Palmer, R.A., Potter, B.S., Helliwell, M., Wright, Colin W. January 2011 (has links)
No / The structure of 5-N-hydroxyethanequindoline hydrochloride methanolate, C17H15ON2 Cl·½CH3OH, M r = 314.78, has been determined from X-ray diffraction data. The crystals are monoclinic, space group C2/c, with Z = 8 molecules per unit cell and a = 18.179(11), b = 7.317(5), c = 24.125(15) Å, β = 110.155(10)°, V c = 3012(3) Å3, crystal density D c = 1.388 Mg m−3. The structure was solved by direct methods, and the asymmetric unit comprises the 5-N-hydroxyethanequindoline hydrochloride and ½CH3OH moiety. The methanol is unusually disordered over a twofold axis with the C atom slightly removed from the twofold axis. Restraints were applied to the bond lengths of the two components of the disordered CH3OH, and to the anisotropic thermal displacement parameters of the disordered CH3OH carbon atom. The heterocyclic quindoline ring system and the first C atom of the hydroxyethane side chain are planar within 0.02 Å, with the terminal C–OH atoms of the side chain significantly out of the plane. The crystal structure is maintained via three hydrogen bonds all involving the chlorine atom an oxygen in the hydroxyethane side chain, a nitrogen in the quindoline moiety and the methanol oxygen.
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Are the Crystal Structures of Enantiopure and Racemic Mandelic Acids Determined by Kinetics or Thermodynamics?Hylton, R.K., Tizzard, G.J., Threlfall, T.L., Ellis, A.L., Coles, S.J., Seaton, Colin C., Schulze, E., Lorenz, H., Seidel-Morgenstern, A., Stein, M., Price, S.L. 08 May 2015 (has links)
Yes / Mandelic acids are prototypic chiral molecules where the sensitivity of crystallized forms (enantiopure/racemic compound/polymorphs) to both conditions and substituents provides a new insight into the factors that may allow chiral separation by crystallization. The determination of a significant number of single crystal structures allows the analysis of 13 enantiopure and 30 racemic crystal structures of 21 (F/Cl/Br/CH3/CH3O) substituted mandelic acid derivatives. There are some common phenyl packing motifs between some groups of racemic and enantiopure structures, although they show very different hydrogen-bonding motifs. The computed crystal energy landscape of 3-chloromandelic acid, which has at least two enantiopure and three racemic crystal polymorphs, reveals that there are many more possible structures, some of which are predicted to be thermodynamically more favorable as well as slightly denser than the known forms. Simulations of mandelic acid dimers in isolation, water, and toluene do not differentiate between racemic and enantiopure dimers and also suggest that the phenyl ring interactions play a major role in the crystallization mechanism. The observed crystallization behavior of mandelic acids does not correspond to any simple “crystal engineering rules” as there is a range of thermodynamically feasible structures with no distinction between the enantiopure and racemic forms. Nucleation and crystallization appear to be determined by the kinetics of crystal growth with a statistical bias, but the diversity of the mandelic acid crystallization behavior demonstrates that the factors that influence the kinetics of crystal nucleation and growth are not yet adequately understood. / EPSRC, Max Planck Society for the Advancement of Sciences, UCL-MPS Impact Ph.D. Fellowship, EU COST Action
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A study of the structure and crystallisation of nanocrystalline zirconiaTucker, Matthew January 1999 (has links)
No description available.
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The phase problem in crystallographyGilmore, C. J. January 2000 (has links)
No description available.
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Structural study of the ferroelectric materials PbNb₂O₆ and PbTa₂O₆Reeve, William Francis January 1999 (has links)
No description available.
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