Gas phase structure of trifluoromethyliminosulfurdifluoride, CF3N=SF2, revisited

The gas phase structure of trifluoromethyliminosulfurdifluoride, CF3N=SF2, was reinvestigated by a joint analysis of gas electron diffraction (GED) an d microwave spectroscopy. Quantum chemical calculations were per formed wit h the HF, MP2 and B3LYP methods using 6-31G* basis sets, The GED intensitie s and MW rotational constants B and C were fitted best with a syn configura tion (CF3 group syn with respect to SF2) and staggered orientation of the C F3 group with large amplitude torsional motion around the C-N bond. The fol lowing skeletal geometric parameters (r(g) distances and r(alpha) angles wi th 2 sigma uncertainties) were derived: S=N 1.477(6) Angstrom, S-F 1.594(2) Angstrom, N-C 1.409(8) Angstrom, C-N=S 127.2(11)degrees, N=S-F 112.7(10)de grees and F-S-F 92.8(4)degrees. The values for the S=N and N-C distances an d for the F-S-F angle differ appreciably from those derived in an earlier G ED investigation. The HF approximation reproduces all bond lengths to withi n +/-0.02 Angstrom and the MP2 and B3LYP calculations predict the S=N and t he S-F bonds to be longer. The bond angles are reproduced very well with al l three methods. (C) 2000 Elsevier Science B.V. All rights reserved.