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3D model (
JSmol)
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ChemSpider | |||
PubChem
CID
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UNII | |||
CompTox Dashboard (
EPA)
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Properties | |||
XeF6 | |||
Molar mass | 245.28 g mol−1 | ||
Density | 3.56 g cm−3 | ||
Melting point | 49.25 °C (120.65 °F; 322.40 K) | ||
Boiling point | 75.6 °C (168.1 °F; 348.8 K) | ||
reacts | |||
Thermochemistry | |||
Std enthalpy of
formation (ΔfH⦵298) |
−294 kJ·mol−1 [1] | ||
Related compounds | |||
Related compounds
|
Krypton hexafluoride | ||
Except where otherwise noted, data are given for materials in their
standard state (at 25 °C [77 °F], 100 kPa).
|
Xenon hexafluoride is a noble gas compound with the formula XeF6. It is one of the three binary fluorides of xenon that have been studied experimentally, the other two being XeF2 and XeF4. All known are exergonic and stable at normal temperatures. XeF6 is the strongest fluorinating agent of the series. It is a colorless solid that readily sublimes into intensely yellow vapors.
Xenon hexafluoride can be prepared by heating of XeF2 at about 300 °C under 6 MPa (60 atmospheres) of fluorine. With
NiF
2 as catalyst, however, this reaction can proceed at 120 °C even in xenon-fluorine molar ratios as low as 1:5.
[2]
[3]
The structure of XeF6 required several years to establish in contrast to the cases of XeF
2 and XeF
4. In the gas phase the compound is
monomeric.
VSEPR theory predicts that due to the presence of six fluoride ligands and one lone pair of electrons the structure lacks perfect
octahedral symmetry, and indeed
electron diffraction combined with high-level calculations indicate that the compound's point group is
C3v. It is a
fluxional molecule.
Oh is only insignificantly higher, indicating that the minimum on the energy surface is very shallow.
[4]
129Xe and 19F NMR spectroscopy indicates that in solution the compound assumes a tetrameric structure: 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".
Six
polymorphs of XeF
6 are known.
[5] including one that contains XeF+
5 ions with bridging F−
ions.
[6]
Xenon hexafluoride hydrolyzes, ultimately affording xenon trioxide: [7]
XeF6 is a Lewis acid, binding one and two fluoride anions:
Salts of the octafluoroxenate(VI) anion (XeF2−
8) are very stable, decomposing only above 400 °C.
[8]
[9]
[10] This anion has been shown to have
square antiprismatic geometry, based on single-crystal X-ray counter analysis of its
nitrosonium salt,
(NO)
2XeF
8.
[11] The sodium and potassium salts are formed directly from
sodium fluoride and
potassium fluoride:
[10]
These are thermally less stable than the caesium and rubidium salts, which are synthesized by first forming the heptafluoroxenate salts:
which are then pyrolysed at 50 °C and 20 °C, respectively, to form the yellow [12] octafluoroxenate salts: [8] [9] [10]
These salts are hydrolysed by water, yielding various products containing xenon and oxygen. [10]
The two other binary fluorides of xenon do not form such stable adducts with fluoride.
XeF
6 reacts with strong fluoride acceptors such as RuF
5
[6] and BrF
3·AuF
3
[13] to form the XeF+
5 cation: