Cubic co-ordination: crystal structure of sodium octafluoroprotactinate(V)

Abstract

The structure of sodium octafluoroprotactinate(V), Na₃PaF₈, has been determined by X-ray diffraction methods and refined by full-matrix least-squares techniques. The crystals are of tetragonal symmetry, in space group I4/mmm(D_4h¹⁷) with a= 5·493 and c= 10·970 Å; Z = 2. Each protactinium atom is bonded to eight fluorine atoms which lie at the corners of an almost perfect cube. The Pa–F bond distance is 2·21 Å. The sodium atoms are located between the PaF₈^3– cubes. Metal–fluorine and fluorine–fluorine distances have been calculated for the isostructural uranium and neptunium compounds, Na₃UF₈ and Na₃NpF₈, respectively.