The trans influence of CF 3: gas phase structure of CF 3SF 5

Abstract

The molecular structure of CF 3SF 5 has been determined by gas electron diffraction. The microwave spectrum was recorded in the frequency range 18–32 GHz. Superimposed on the essentially symmetric top transitions are found perturbations due to the large amplitude torsional motion of the CF 3 group. Therefore, a joint analysis of the electron diffraction intensities and rotational constant was not attempted. An approximate valence force field has been derived and used to calculate vibrational amplitudes. The structure is based on a slightly distorted octahedron with the following zkeletal parameters (r a values, 2σ in parentheses): SF a = 1.562(7) A, SF e = 1.572(2) A, SC = 1.887(8) A and CSF e = 90.5(2)°. The axial SF bond ( trans to CF 3) in shorter by 1.010(7) A than the equational bonds and the mean SF distances are longer by 0.008(2) A than the bonds in SF 0. The SF bond lengths are discussed together with analogous bond lengths in other XSF 5 derivatives on the basis of the VSEPR model and “ trans influence” concept. The variation of the SCF 3 distance with the sulfur oxidation state is analyzed.