Electron diffraction study of perfluorodisiloxane

The molecular structure of perfluorodisiloxane (SiF3)2O has been determined by the sectormicrophotometer method of electron diffraction. The Si—F bond length is 1.554 ± 0.010 Å, the Si—O bond length is 1.580 ± 0.025 Å, the Si—O—Si angle is 155.7 ± 2.0° and the F—Si—F angle is 108.8 ± 0.5°. The relatively large uncertainties in these values arise from the closeness of the values of the Si—O and Si—F distances (and hence the F …(Si)…F and F …(Si)…O distances); the Si—O and Si—F bond distances are strongly correlated. The relative conformation of the trifluorosilyl groups has been studied in detail; the angle of twist refines to a value of 34.6 ± 1.5°.