Die Kryolithstruktur von Na3ScF6 und die Oktaederkippung in isostrukturellen Natriumhexafluorometallaten Na3MF6

The Cryolite Structure of Na₃ScF₆ and the Tilting of Octahedra in Isostructural Sodium Hexafluorometallates Na₃MF₆ X-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.