Structural study of the cesium oxypentafluorouranate (VI) CsUOF5

Abstract

Powder samples of cesium oxypentafluorouranate(VI) were studied by both neutron diffraction and 19F broad Une nuclear magnetic resonance.CsUOF5 crystallises with the [Formula: see text] space group, with the parameters a = 5.41 ± 0.01 Ǻ; α = 95°34′ ± 5′. The structure, which was found to be unchanged at temperatures as low as 4.2 K, was interpreted by a statistical occupation of six-fold equivalents sites, the occupation rate being 1/6 and 5/6 for oxygen and fluorine, respectively. The nmr study showed that the disorder corresponding to this structure was of dynamic type, and that the UOF5− ions were in isotropical rotation. The motion is observable at temperatures as low as 223 K with a characteristic time τ equal to3 × 10-5 s at 266 K. On the other hand, it was also shown through this nmr study that the point symmetry of the UOF5− ion corresponds to the C4v group, with the axial fluorine being more covalent than the equatorial ones. Consistency of the diffraction and nmr results is discussed.