Molecular structure of tris(trifluoromethylthio)amine by gas-phase electron diffraction and nuclear magnetic resonance spectroscopy

Abstract

The structure and amplitudes of vibration of N(SCF₃)₃ have been investigated by electron diffraction. Principal structural parameters and uncertainties (3σ) are: r_g(C–F) 1.336(2), r_g(C–S) 1.825(6), and r_g(S–N) 1.705(5)Å; S–N–S 118.8(0.7), N–S–C 100.1 (1.0), and F–C–F 108.3(0.3)°. The CF₃ groups, in or close to staggered conformations, are tilted by 4.8(0.6)°. The molecule appears not to possess C₃ symmetry. The NSC planes are perpendicular (within experimental uncertainties) to the S₃ plane. Two CF₃ groups lie above this plane, one below it. Fluorine-19 n.m.r. spectra show a single line at room temperature, but split into two components of relative intensity 2 : 1 below ca.–65 °C. From an analysis of line shapes, the barrier to internal rotation about an S–N bond has been found to be 6(1) kcal mol^–1. The near planarity of the NS₃ skeleton is discussed in terms of p→dπ bonding and steric interactions. Results of semiempirical molecular-orbital calculations on a model compound are analysed.