An Electron Diffraction Investigation of the Molecular Structures of Silicon Tetrabromide, Tribromosilane, and Dibromodifluorosilane

The bond lengths in the halides of the fourth, fifth, and sixth group elements are in general considerably shorter than the sums of the corresponding Pauling-Huggins covalent radii. This discrepancy appears to be partially resolved by the introduction of a correction for the partial ionic character of the bonds; however, large disparities remain for the second row fluorides, while for the heavier halides the agreement is not precise. For the bromosilanes considered in this paper, the Si-Br distances are found to be 2.16 ± 0.03 Å., 0.06 Å. shorter than the distance calculated by Schomaker and Stevenson. The bond-angle values reported here are all approximately tetrahedral with the exception of that for F-Si-F in SiF_2Br_2, which seems to be decidedly less than tetrahedral. This value may be in error, however, as noted below.