The molecular structure of N-fluorobis(trifluoromethanesulfonyl)imide, NF(SO2CF3)2, as studied in the gas phase by electron diffraction restrained by ab initio calculations

Abstract

The structure of N-fluorobis(trifluoromethylsulfonyl)imide, prepared by a relatively safe and easy method, has been determined by gas-phase electron diffraction (GED), employing the SARACEN method, with flexible restraints based on the MP2/6-311G* structure, and by X-ray crystallography at 150 K. The strongly electron-withdrawing CF₃ and SO₂CF₃ groups make the C–S and N–S distances long, averaging 187.7(3) and 171.7(3) pm, respectively, in the gas phase. The gas consists of two conformers, one (75%) with a CF₃ group on each side of the SNS plane, one anti-periplanar and one syn-periplanar to the further N–S bond (ap, sp), and the other with both CF₃ groups on the same side, i.e. denoted ap, ap. These conformers have very different SNS angles, 126.9(9)° and 117.1(17)° respectively. In the crystal all molecules have the ap, sp conformation, with parameters similar to those found for this conformer in the gas phase.