When antimony pentafluoride is refluxed with sulphur trioxide, a new compound with the composition SDF5SO3 is formed together with sulphuryl fluoride, disulphuryl fluoride, and small amounts of the higher polysulphuryl fluorides. This compound is a colorless, very viscous liquid. From the chemical analysis, the F19 NMR spectrum, and the Raman and infrared spectra of the liquid it was concluded that the compound is antimony tetrafluoride ...