Fluoride crystal structures. Part XI. Trifluoroselenium(IV) hexafluoroniobate(V) and hexafluorotantalate(V)

Abstract

The interaction of selenium tetrafluoride and tantalum pentafluoride at room temperature, or niobium pentafluoride at 106° produces the adducts SeF₄,TaF₅ and SeF₄,NbF₅. Crystals of these adducts are rhombohedral, space group R3, with identical unit-cell dimensions, a= 8·99 Å, α= 92·9°. The structure of the niobium pentafluoride adduct was refined by three-dimensional least-squares methods, the final R being 0·090 for 724 reflections. The atomic arrangement is consistent with the ionic formulation [SeF₃]⁺[NbF₆]^– with substantial fluorine bridging between the ions to form tetrameric units.