The adduct XeF 2·2SbF 5: Its crystal structure and thermochemistry

Abstract

Crystals of XeF 2·2SbF 5 are monoclinic, spacegroup P2 1 a = 8·07, b = 9·55, c = 7·33 A ̊ , β = 105·8° . A least squares analysis of 828 reflexion intensities, measured by photographic methods, has converged with R = 0·104. The molecular structure of the adduct is derived from the formulation XeF +Sb 2F 11 −, but from an analysis of the intra and intermolecular geometry it is concluded that the adduct has considerable covalent character. The enthalpy of hydrolysis of XeF 2·2SbF 5 in M NaOH is −280·7 kcal mole −1. From this result a value of ΔH f φ (XeF 2·2SbF 5(c)) = −705 kcal mole −1 has been deduced. The enthalpy of the reaction 2SbF 5( l) + F −( g) = Sb 2F 11 − ( g), which is a measure of the fluoride ion affinity of antimony pentafluoride, has thence been estimated as ca. −137 kcal mole −1.