The structures of fluorides. I. Deviations from ideal symmetry in the structure of crystalline UF₆: a neutron diffraction analysis

A neutron-diffraction powder pattern of crystalline UF₆ at 21°C has confirmed the X-ray structure of Hoard & Stroupe [USAEC Report TID-5290 (1958) Paper 45]. From the X-ray data it was not certain whether the fluorine atoms deviated significantly from ideal hexagonal close-packing and the UF₆ octahedra from regularity. The neutron powder pattern of UF₆ was analysed by the profile-fitting method of Rietveld [Acta Cryst. (1967). 22, 151]. Significant deviations from the ideal parameters of Hoard & Stroupe were found. These effects are apparently caused by strong U–U repulsions in the unsymmetrical U^VI arrangement and the U–F bonding in the octahedra.