The Molecular Structure and Force Constants of Antimony Tribromide as Determined by Gas-phase Electron Diffraction

The molecular structure and mean amplitudes of SbBr3 at 102°C have been determined by the sector-microphotometer method of gas-phase electron diffraction to be as follows: rg(Sb-Br)=2.490±0.003 Å, rg(Br-Br)=3.76±0.01 Å, θα=98.2°±0.6°, l(Sb–Br)=0.060±0.003 Å and l(Br–Br)=0.15±0.01 Å. General quadratic force constants have been determined from the observed mean amplitudes and vibrational frequencies. The molecular structure supports the validity of the empirical rules between a bond length and the covalent radii and electronegativities of its constituent atoms. An empirical equation, θ(YXY)=92+8xX−3xY(+xZ), has been proposed for the bond angles of Vb-group halides, (Z)XY3, and the electronegativities, x.