An X-ray crystallographic study of [Xe2F3][SbF6] and dimorphism in [Xe2F3][AsF6]; and a density functional theory study of the Xe2F3+ cation

The Xe2F3+ cation has been studied by X-ray crystallography with AsF6− and SbF6− as counter anions. The [Xe2F3][AsF6] salt was found to be dimorphic with a monoclinic phase: C2/c, a=25.756(3) Å, b=8.556(1) Å, c=15.356(2) Å, β=126.592(5)°, V=2716.9(6) Å3, Z=12 and R1=0.0389 at −127°C; and a trigonal phase: P3221, a=8.602(5) Å, c=10.665(9) Å, V=683.4(8) Å3, Z=3 and R1=0.0385 at −116°C. The [Xe2F3][SbF6] salt crystallizes in the monoclinic system: C/c, a=14.575(2) Å, b=8.1081(12) Å, c=9.926(14) Å, β=130.360(3)°, V=899.8(2) Å3, Z=4 and R1=0.0319 at −127°C. The Xe···Fb···Xe bridge angle of the V-shaped Xe2F3+ cation was found to vary from 139.8(8) to 160.3(3)° in trigonal [Xe2F3][AsF6] and [Xe2F3][SbF6], respectively. The variation in the Xe···Fb···Xe bridge angle is attributed to crystal packing effects. The geometry and vibrational frequencies of the Xe2F3+ cation were calculated using density functional theory methods, confirming the experimental evidence for the facile deformation of the Xe···Fb···Xe bridge angle. The vibrational spectrum of Xe2F3+ has been reassigned based on the theoretical calculations.