Knowledge Bank

Xenon hexafluoride has been found by gas-phase electron diffraction to be distorted from $Oh$ symmetry. The best fit of diffraction data was obtained for a distorted pentagonal bipyramidal structure with a vacant site on the equator. Bond lengths and axial angles follow Gillespie's rules for a seven-coordinated structure with the central atom lone pair occupying the vacant equatorial site. The equatorial FXeF bond angles of $82\circ$, however, are deformed from $90\circ$ by much less than the amount predicted by Gillespie's rules. Large bending amplitudes of vibration were observed for the F atoms adjacent to the protruding Xe lone pair. This suggests that the molecule frequently passes through one of its several barriers to inversion and changes the direction of its lone pair. If this inversion is faster than molecular rotation, the molecule may exhibit the unusual property of possessing a dipole moment in its equilibrium configuration, yet exhibiting a zero dipole moment in any conventional measurement. Structural and vibrational parameters will be reported.