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  • 1
    ISSN: 0044-2313
    Keywords: Sodium scandium fluoride ; cryolite structure ; tolerance factor ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: The Cryolite Structure of Na3ScF6 and the Tilting of Octahedra in Isostructural Sodium Hexafluorometallates Na3MF6X-ray studies at single crystals of Na3ScF6 confirmed the monoclinic cryolite type structure of this compound: a = 559.5, b = 580.2, c = 811.6 pm, β = 90.72°, Z = 2, space group P21/n; R1 = 0.021 for 512 symmetry independent reflections. The octahedra of [ScF6] (average Sc—F = 200.7 pm), as well as those of [NaF6] (Na1—F = 229.1 pm) linked to them, are titled by about 20° with respect to the axes of the perovskite-like pseudocell. This tilting of octahedra is discussed in comparison with other cryolites and with orthorhombic perovskites NaMF3; there results a correlation between tilt angle and tolerance factor t ˜ 0.88 of these compounds, the [NaF8] coordination of which invariably exhibits a constant mean value of Na2—F = 231.5 ± 1 pm for the four shortest distances.
    Notes: Eine röntgenographische Untersuchung an Einkristallen von Na3ScF6 bestätigte die monokline Kryolithstruktur dieser Verbindung: a = 559,5, b = 580,2, c = 811,6 pm, β = 90,72°, Z = 2, Raumgruppe P21/n; R1 = 0,021 für 512 symmetrie-unabhängige Reflexe. Die [ScF6]-Oktaeder (Mittelwert Sc—F = 200,7 pm) sind ebenso wie die mit ihnen verknüpften [NaF6]-Oktaeder (Na1—F = 229,1 pm) um etwa 20° gegen die Richtungen der perowskitartigen Pseudozelle gekippt. Diese Oktaederkippung wird im Vergleich mit anderen Kryolithen und mit den orthorhombischen Perowskiten NaMF3 diskutiert; dabei ergibt sich ein Zusammenhang zwischen Kippungswinkel und Toleranzfaktor t 〈 0,88 für diese Verbindungen, in deren [NaF8]-Koordination sich einheitlich ein konstanter Mittelwert von Na2—F = 231,5 ± 1 pm für die vier kürzesten Abstände zeigt.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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