Xenon hexafluoride

Xenon hexafluoride is the chemical compound with the formula XeF6. This colorless crystalline compound is one of the three binary fluorides of xenon, the other two being XeF2 and XeF4. All are exergonic and stable at normal temperatures. XeF6 is the strongest fluorinating agent of the series.

Xenon hexafluoride can be prepared by long-term heating of XeF2 at about 300 degrees and pressure 6 MPa.

Structure
The structure of XeF6 required several years to establish in contrast to the cases of xenon difluoride and xenon tetrafluoride. In the gas phase it adopts a slightly distorted octahedral geometry. It lacks perfect octahedral symmetry, as predicted by VSEPR theory due to the presence of six fluoride ligands and one lone pair of electrons. According to Konrad Seppelt, the Associate Professor of Chemistry at the University of Heidelberg, "the structure is best described in terms of a mobile electron pair that moves over the faces and edges of the octahedron and thus distorts it in a dynamic manner.". NMR spectra of129Xe19F6 indicate that it is tetrameric: four equivalent xenon atoms are arranged in a tetrahedron surrounded by a fluctuating array of 24 fluorine atoms that interchange positions in a "cogwheel mechanism".

Reactions
Xenon hexafluoride hydrolyzes stepwise, ultimately affording xenon trioxide:
 * XeF6 + H2O →  XeOF4  +  2 HF
 * XeOF4 + H2O →  XeO2F2  +  2 HF
 * XeO2F2 +  H2O  →  XeO3  +  2 HF

XeF6 serves as a Lewis acid, binding one and two fluoride anions:
 * XeF6 + F− → XeF7−
 * XeF7− + F− → XeF82−

The two other binary fluorides do not form such stable adducts with fluoride. The salt Rb2XeF8 is among the most robust xenon compounds, decomposing only above 400 °C.