Struktur und Bindung in Übergangsmetall-Fluoriden MIIMeIVF6: Neutronenbeugungs-Strukturuntersuchungen an CaSnF6, FeZrF6, und CrZrF6 |
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Authors: | HW Mayer D Reinen G Heger |
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Institution: | Fachbereich Chemie der Universität, D-3550 Marburg, Hans-Meerwein-Strasse, die Bundesrepublik;Kernforschungszentrum Karlsruhe, Institut für Nukleare Festkörperphysik, D-7500 Karlsruhe 1, Postfach 3640, die Bundesrepublik |
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Abstract: | Compounds MIIMeIVF6 requently undergo phase transitions from the cubic ordered ReO3 to the trigonal LiSbF6 structure when lowering the temperature. In case of a strongly Jahn-Teller unstable cation in the MII position additional phases may occur. Results of powder neutron-diffraction studies on CaSnF6, FeZrF6, and CrZrF6 at different temperatures are reported. The high-temperature phases have the space group Fm3m; the F? ligands are either statistically displaced from the MIIMeIV directions or undergo a strong thermal motion perpendicular to these directions (: 165–180°). The thermal ellipsoids of the CrF bonds are strongly indicative of a dynamical Jahn-Teller effect in addition. In the low-temperature phases of CaSnF6 and FeZrF6 (space group ) the is more distinctly bent (?155–160°). CrZrF6 undergoes two reversible phase transitions, which are determined to occur at 415 ± 5 K (cubic → tetragonal, dynamic to static Jahn-Teller distortion of CrF6 octahedra and 150 ± 10 K (tetragonal → (pseudo)monoclinic). |
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