Acta Cryst. (2008). B64, 645-651 [ doi:10.1107/S0108768108033053 ]
Abstract: Dioxotetrafluorotungstates (NH4)2WO2F4 [(I) at 297 K and (II) at 133 K] and Rb2WO2F4 (III) were synthesized in a single-crystal form and their structures were determined by X-ray diffraction. Two independent states of the cis-WO2F4 octahedron are characteristic of static and dynamic disorder in structure (I). Dynamically disordered W2 is displaced from the symmetry axis producing four possible orientations of anion that permits O and F atoms to be identified in separate orientations owing to the inherent differences between W-O and W-F bonding. After the phase transition at lower temperature (201 K), (I) transforms into the twin structure (II) with complete O/F ordering. Structure (III) is characterized by full O/F static disorder without any phase transitions at lower temperature.
Keywords: oxofluorotungstates; dynamic and static orientational disorder; reorientation motions; NMR; Raman spectra; phase transition; twin structure.
 |   Structure factor file (CIF format) (50.4 kbytes) |
| Structure factor file (CIF format) (311.0 kbytes) |
| Structure factor file (CIF format) (11.4 kbytes) |
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