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Struktur und Bindung in Übergangsmetall-FluoridenMIIMeIVF6:Neutronenbeugungs-Strukturuntersuchungen an CaSnF 6, FeZrF 6, und CrZrF 6

Authors
Journal
Journal of Solid State Chemistry
0022-4596
Publisher
Elsevier
Publication Date
Volume
50
Issue
2
Identifiers
DOI: 10.1016/0022-4596(83)90190-1

Abstract

Abstract Compounds M IIMe IVF 6 requently undergo phase transitions from the cubic ordered ReO 3 to the trigonal LiSbF 6 structure when lowering the temperature. In case of a strongly Jahn-Teller unstable cation in the M II position additional phases may occur. Results of powder neutron-diffraction studies on CaSnF 6, FeZrF 6, and CrZrF 6 at different temperatures are reported. The high-temperature phases have the space group Fm3 m; the F − ligands are either statistically displaced from the M IIMe IV directions or undergo a strong thermal motion perpendicular to these directions ( ∢M II  FMe IV : 165–180°). The thermal ellipsoids of the CrF bonds are strongly indicative of a dynamical Jahn-Teller effect in addition. In the low-temperature phases of CaSnF 6 and FeZrF 6 (space group R 3 ) the ∢M II  FMe IV is more distinctly bent (⋍155–160°). CrZrF 6 undergoes two reversible phase transitions, which are determined to occur at 415 ± 5 K (cubic → tetragonal, dynamic to static Jahn-Teller distortion of CrF 6 octahedra and 150 ± 10 K (tetragonal → (pseudo)monoclinic).

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