Transition-metal tetrafluoride oxide–antimony pentafluoride adducts; preparation and characterization of the adducts MF4O·SbF5(M = Mo, W, or Re) and crystal structures of MoF4O·SbF5 and ReF4O·SbF5

Abstract

The adducts MF₄O·SbF₅(M = Mo, W, or Re) have been obtained as colourless (Mo, W) or pale blue (Re) solids from the reaction of the appropriate tetrafluoride oxide with excess of SbF₅. The solid adducts have been characterized by observation of reaction stoicheiometries, Raman and mass spectra, and by X-ray diffraction. Crystals of MoF₄O·SbF₅ are monoclinic, space group P2₁/n, with unit-cell dimensions a= 7.470(8), b= 10.40(2), c= 9.606(9)Å, β= 93.13(30)°, and Z= 4; those of ReF₄O·SbF₅ are monoclinic, space group P2₁/c, with unit-cell dimensions a= 5.561(10), b= 10.198(8), c= 12.622(9)Å, β= 99.37(20)°, and Z= 4. Both structures have been refined by three-dimensional least-squares methods to R= 0.041 3 for 1 123 reflections for MoF₄O·SbF₅ and R= 0.057 6 for 1 062 reflections for ReF₄O·SbF₅. The molybdenum adduct is best regarded as a polymeric zigzag chain in which alternate Sb and Mo atoms are linked through fluorine bridges. The rhenium adduct, on the other hand, contains dimers, with two Re atoms and two Sb atoms, linked through fluorine bridges into distorted, essentially covalent eight-membered rings. Evidence has also been obtained for a second adduct of molybdenum, MoF₄O·2SbF₅. An estimate of the ionic contribution to bonding in the adducts is made.