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STRUCTURES OF SYNTHETIC K2MGSI5O12 LEUCITES BY INTEGRATED X-RAY-POWDER DIFFRACTION, ELECTRON-DIFFRACTION AND SI-29 MAS NMR METHODS
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UNSPECIFIED (1994) STRUCTURES OF SYNTHETIC K2MGSI5O12 LEUCITES BY INTEGRATED X-RAY-POWDER DIFFRACTION, ELECTRON-DIFFRACTION AND SI-29 MAS NMR METHODS. ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 50 (Part 1). pp. 31-41. ISSN 0108-7681.
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Abstract
The structures of disordered and ordered varieties of the title compound have been determined using integrated TEM, MAS NMR and Rietveld analysis of synchrotron X-ray powder diffraction data. Both samples have a 'leucite-like' framework topology. The dry-synthesized sample is cubic, Ia3d [a = 13.4190 (1) angstrom, V = 2416.33 (5) angstrom3] with disordered Mg and Si in tetrahedral framework sites. The hydrothermally synthesized analogue is monoclinic, P2(1)/c [a = 13.168 (5), b = 13.652 (1), c = 13.072 (5) angstrom, beta = 91.69-degrees, V = 2348 (2) angstrom3], and has a fully ordered framework with four K, ten Si and two Mg sites per 24 O atoms (one quarter of the unit cell). Two of these Si sites are linked to Si tetrahedra only [Q4(4Si)], while the other eight Si sites have one Mg and three Si tetrahedra as next-nearest neighbours [Q4(3Si, 1 Mg)]. Q4(4Si) and Mg tetrahedra share opposite comers of four rings. Si and Mg ordering is accompanied by a volume contraction of 2.8%. The X-ray structural data for the ordered sample allow the Si-29 MAS NMR peaks to be assigned to particular Si tetrahedra, and thus to particular values of the mean T-O-T angle. The nature of the polymorphism between the disordered and ordered samples is discussed and related to the different synthesis conditions. Water in the hydrothermal synthesis accelerates Si-Mg ordering, allowing the thermodynamically more stable phase to be formed.
Item Type: | Journal Article | ||||
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Subjects: | Q Science > QD Chemistry | ||||
Journal or Publication Title: | ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE | ||||
Publisher: | MUNKSGAARD INT PUBL LTD | ||||
ISSN: | 0108-7681 | ||||
Official Date: | 1 February 1994 | ||||
Dates: |
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Volume: | 50 | ||||
Number: | Part 1 | ||||
Number of Pages: | 11 | ||||
Page Range: | pp. 31-41 | ||||
Publication Status: | Published |
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