The crystal structure of Li 4UF 8

Abstract

The compound Li 4UF 8 crystallizes in space group Pnma with a 0 = 9·960, b 0 = 9·883 and c 0 = 5·986. The X-ray density is 4·71 g/cm 3 and Z = 4. Twenty-four positional parameters, four anisotropic uranium temperature factors, and seven isotropic temperature factors were determined from 634 independent reflections measured by the 2θ-scan technique with a scintillometer. The parameters were refined by least squares to an R factor of 0·082. Absorption corrections were made for Cu Kα radiation on an oblate spheroid with a short 36 μ axis, [001], and a 64 μ dia. for the circular section. The U 4+ ion has 8F − nearest neighbors with bond distances of 2·21–2·39 Å. The next three nearest neighbors are 2Li + and another F − at 3·27 and 3·30 Å respectively. The nine F − ions are at the corners of a 14-faced polyhedron which has the form of a triangular prism with pyramids on each of the three prism faces and the two Li + ions are at the centers of irregular F − octahedra which share faces with the uranium polyhedron. The Li +F − distances are 1·82–2·28 Å.