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Solving complex open-framework structures from X-ray powder diffraction by direct-space methods using composite building units
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
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2013 (English)In: Journal of applied crystallography, ISSN 0021-8898, E-ISSN 1600-5767, Vol. 46, 1094-1104 p.Article in journal (Refereed) Published
Abstract [en]

The crystal structure of a novel open-framework gallogermanate, SU-66 {|(C6H18N2)(18)(H2O)(32)|[Ga4.8Ge87.2O208]}, has been solved from laboratory X-ray powder diffraction (XPD) data by using a direct-space structure solution algorithm and local structural information obtained from infrared (IR) spectroscopy. IR studies on 18 known germanates revealed that the bands in their IR spectra were characteristic of the different composite building units (CBUs) present in the structures. By comparing the bands corresponding to Ge-O vibrations in the IR spectra of SU-66 with those of the 18 known structures with different CBUs, the CBU of SU-66 could be identified empirically as the Ge-10(O,OH)(27) cluster (Ge-10). The unit cell and space group (extinction symbol P--a; a = 14.963, b = 31.593, c = 18.759 angstrom) were determined initially from the XPD pattern and then confirmed by selected-area electron diffraction. The structure of SU-66 was solved from the XPD data using parallel tempering as implemented in FOX [Favre-Nicolin & Cerny (2002). J. Appl. Cryst. 35, 734-743] by assuming P2(1)ma symmetry and two Ge-10 clusters in the asymmetric unit. Rietveld refinement of the resulting structure using synchrotron XPD data showed the framework structure to be correct and the space group to be Pmma. The framework has extra-large (26-ring) onedimensional channels and a very low framework density of 10.1 Ge/Ga atoms per 1000 angstrom(3). SU-66, with 55 framework atoms in the asymmetric unit, is one of the more complicated framework structures solved from XPD data. Indeed, 98% of the reflections were overlapping in the XPD pattern used for structure solution. Tests on other open-framework germanates (SU-62, SU-65, SU-74, PKU-12 and ITQ-37) for which the XPD data, unit cell, space group and IR spectra were available proved to be equally successful. In a more complex case (SU-72) the combination of FOX and powder charge flipping was required for structure solution.

Place, publisher, year, edition, pages
2013. Vol. 46, 1094-1104 p.
National Category
Chemical Sciences
URN: urn:nbn:se:su:diva-93305DOI: 10.1107/S0021889813013101ISI: 000322032300037OAI: diva2:646109
VinnovaSwedish Research Council


Available from: 2013-09-06 Created: 2013-09-06 Last updated: 2013-09-06Bibliographically approved

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Inge, A. KenFahlquist, HenrikWillhammar, TomZou, Xiaodong
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