Gas-phase molecular structures of bis(difluorophosphino) sulphide, S(PF2)2, bis(difluorophosphino) selenide, Se(PF2)2, and difluoro(methylthio)phosphine, PF2(SMe), determined by electron diffraction

Abstract

The molecular structures of S(PF₂)₂ and Se(PF₂)₂ in the gas phase have been determined by electron diffraction. Both molecules have average structures with C_2v symmetry, but have large-amplitude torsional vibrations, root mean square torsion angles being 22(2) and 20(4)° respectively. Principal parameters (r_a) are: S(PF₂)₂, r(P–S) 213.2(4), r(P–F) 157.2(2) pm, FPF 97.4(5), FPS 100.2(4), PSP 91.3(11)°; for Se(PF₂)₂, r(P–Se) 227.3(5), r(P–F) 157.3(3) pm, FPF 100.6(11), FPSe 98.7(4), PSeP 94.6(8)°. The structure of PF₂(SMe) has also been determined. Three conformations fit the observed data almost equally well, with the PF₂ group twisted 19(3), 106(9) or 171(5)° away from the position in which the S–C bond lies anti to the bisector of the FPF angle. The most favoured structure is the second of these, for which other principal parameters (r_a) are r(P–S) 208.5(3), r(P–F), 158.9(3), r(C–S) 182.2(5) pm, FPF 95.6(6), SPF 101.2(3), PSC 102.0(12)°.