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  • Articles  (2)
  • International Union of Crystallography (IUCr)  (2)
  • 1995-1999  (2)
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  • Articles  (2)
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  • 1
    Electronic Resource
    Electronic Resource
    The use of CCD area detectors in charge-density research. Application to a mineral compound: the α-spodumene LiAl(SiO3)2 (1999)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 55 (1999), S. 867-881 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: X-ray diffraction data sets collected on both Nonius and Siemens (Bruker) goniometers equipped with charge-coupled device (CCD) area detectors have been tested for the electron-density determination of the aluminosilicate mineral compound α-spodumene LiAl(SiO3)2, aluminium lithium silicon oxide. Data collection strategies, reflection intensity peak integration methods and experimental error estimates are different for the two instruments. Therefore, the consistency and quality of the two types of CCD measurements have been carefully compared to each other and to high-resolution data collected on a conventional CAD-4 point-detector diffractometer. Multipole density model refinements were carried out against the CCD data and the statistical factors analysed in terms of experimental weighting schemes based on the standard uncertainties of the diffraction intensities derived by the Nonius and Siemens software programs. Consistent experimental electron-density features in the Si–O–Si and Si–O–Al bridges were found from both CCD data sets. The net atomic charges obtained from the kappa refinements against each CCD data set are also in good agreement and quite comparable with the results of the conventional CAD-4 experiment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108768199006953
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  • 2
    Electronic Resource
    Electronic Resource
    Experimental evidence for the amino-group non-planarity in nitroanilines: neutron diffraction study of 2-methyl-5-nitroaniline at 100 K (1999)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 55 (1999), S. 209-215 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: An appreciable degree of pyramidalization of the amine N atom is observed in the title compound. The existence of polar chains, induced by N—H...O synthons, is confirmed. C—H...O interactions, not noted in a previous X-ray study, were found to stabilize further the known head-to-tail assembling of the chains. The structure can be described as non-polar (101) layers, embodying chains interlinked by centrosymmetric dimers, connected by C(aryl)—H...π interactions. The latter are not present in m-nitroaniline, 2-methyl-4-nitroaniline and other related compounds with chains built from similar N—H...O synthons and assembled head-to-head. This finding implies that an obvious relationship between molecular recognition patterns and crystal structures should not be assumed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108768198010349
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    Paper (German National Licenses)
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