The molecular structure of gaseous bis(trifluoromethyl)selenium difluoride as determined by electron diffraction

Abstract

The structure of gaseous bis(trifluoromethyl)selenium difluoride has been determined by electron diffraction. Hence the predominant species is shown to be the monomer (CF3)2SeF2 with the CF3 ligands occupying the equatorial sites of a framework derived from a trigonal bipyramid. Salient structural parameters (ra) are: r(Se–F) 182.7(0.5), r(Se–C) 202.2(0.8), and r(C–F) 131.4(0.3) pm; F–Se–F 157.8(3.5), C-Se–C 118.7(1.7), and F–C–Se 108.9(0.4)°. The molecule has C2 symmetry overall, with the CF3 groups twisted 19.8(1.1)° away from the positions in which one C–F bond of each group is anti with respect to an Se–C bond (corresponding to a conformation having C2V symmetry overall). Comparisons with the structures of related molecules show that the switch from SeF4 to (CF3)2SeF2, unlike that from SF4 to (CF3)2SF2, results in an increase in the equatorial bond angle, in keeping with the expectations of the valence shell electron pair repulsion model.