Vibrational amplitudes for thionyl tetrafluoride and sulphur tetrafluoride

Abstract

The potential energy constants and vibrational mean amplitudes for thionyl tetrafluoride were calculated using the Urey-Bradley Force Field (UBFF) with a view to finding out the influence of the oxygen atom on the SF4 group. It was found that the axial S-F stretching force constant is smaller than the equatorial S-F stretching force constant, which is consistent with the variation in the bond length. The behaviour of the oxygen atom is found to be similar to the lone pair of electrons in sulphur tetrafluoride. The vibrational mean amplitudes calculated from spectroscopic data are in very good agreement with the electron diffraction data. The large root mean square amplitude of vibration for equatorial-equatorial non-bonded fluorine atoms (0.099 Ǻ) in sulphur tetrafluoride indicates the possibility of incomplete inversion as pointed out by Chantry and Ewing.

Molecular force field for bromine pentafluoride

“…If this is accepted then one should expect that this unpaired electron will have its own influence on molecular force constants. Previous work (7)(8)(9)(10)(11)(12) for molecules having unpaired electrons gave more consistent and chemically meaningful force constants, and many ambiguities in the explanation of the results of normal coordinate analysis of these molecules vanished. As such it is thought worthwhile to extend this modified approach to the BrF, molecule.…”