Xenon hexafluoride

Xenon hexafluoride
Structural formula	Space-filling model
Identifiers
CAS Number	13693-09-9 ;
3D model (JSmol)	Interactive image;
ChemSpider	123066 ;
PubChem CID	139546;
UNII	WXC3I4P46T ;
CompTox Dashboard (EPA)	DTXSID80160010 ;
	InChI InChI=1S/F6Xe/c1-7(2,3,4,5)6 Key: ARUUTJKURHLAMI-UHFFFAOYSA-N ; InChI=1/F6Xe/c1-7(2,3,4,5)6 Key: ARUUTJKURHLAMI-UHFFFAOYAF;
	SMILES F[Xe](F)(F)(F)(F)F;
Properties
Chemical formula	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)
Solubility in water	reacts
Thermochemistry
Std enthalpy of; formation (ΔfH⦵298)	−294 kJ·mol−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). verify (what is ?) Infobox references

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.

Preparation

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]

Structure

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 C_3v. It is a fluxional molecule. O_h 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]

Reactions

Hydrolysis

Xenon hexafluoride hydrolyzes, ultimately affording xenon trioxide:^[7]

XeF₆ + H₂O → XeOF₄ + 2 HF

XeOF₄ + H₂O → XeO₂F₂ + 2 HF

XeO₂F₂ + H₂O → XeO₃ + 2 HF

XeF₆ + 3 H₂O → XeO₃ + 6 HF

XeF₆ is a Lewis acid, binding one and two fluoride anions:

XeF₆ + F⁻ → XeF⁻
₇

XeF⁻
₇ + F⁻ → XeF²⁻
₈

Octafluoroxenates

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]

2 NaF + XeF
₆ → Na
₂XeF
₈

2 KF + XeF
₆ → K
₂XeF
₈

These are thermally less stable than the caesium and rubidium salts, which are synthesized by first forming the heptafluoroxenate salts:

CsF + XeF
₆ → CsXeF
₇

RbF + XeF
₆ → RbXeF
₇

which are then pyrolysed at 50 °C and 20 °C, respectively, to form the yellow^[12] octafluoroxenate salts:^[8]^[9]^[10]

2 CsXeF
₇ → Cs
₂XeF
₈ + XeF
₆

2 RbXeF
₇ → Rb
₂XeF
₈ + XeF
₆

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.

With fluoride acceptors

XeF
₆ reacts with strong fluoride acceptors such as RuF
₅^[6] and BrF
₃·AuF
₃^[13] to form the XeF⁺
₅ cation:

XeF
₆ + RuF
₅ → XeF⁺
₅RuF⁻
₆

XeF
₆ + BrF
₃·AuF
₃ → XeF⁺
₅AuF⁻
₄ + BrF
₃

References

^ Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A23. ISBN 978-0-618-94690-7.
^ Melita Tramšek; Boris Žemva (December 5, 2006). "Synthesis, Properties and Chemistry of Xenon(II) Fluoride" (PDF). Acta Chim. Slov. 53 (2): 105–116. doi:10.1002/chin.200721209. Archived from the original (PDF) on May 12, 2013. Retrieved July 10, 2009.
^ Chernic, C. L.; Malm, J. G. (2007). "Xenon Hexafluoride". Inorganic Syntheses. Vol. VIII. pp. 258–260. doi:10.1002/9780470132395.ch68. ISBN 9780470132395.
^ Seppelt, Konrad (June 1979). "Recent Developments in the Chemistry of Some Electronegative Elements". Accounts of Chemical Research. 12 (6): 211–216. doi:10.1021/ar50138a004.
^ Hoyer, S.; Emmler, K.; Seppelt, T. (October 2006). "The structure of xenon hexafluoride in the solid state". Journal of Fluorine Chemistry. 127 (10): 1415–1422. Bibcode:2006JFluC.127.1415H. doi:10.1016/j.jfluchem.2006.04.014. ISSN 0022-1139.
^ ^a ^b James E. House (2008). Inorganic Chemistry. Academic Press. p. 569. ISBN 978-0-12-356786-4.
^ Appelman, E. H.; J. G. Malm (June 1964). "Hydrolysis of Xenon Hexafluoride and the Aqueous Solution Chemistry of Xenon". Journal of the American Chemical Society. 86 (11): 2141–2148. doi:10.1021/ja01065a009.
^ ^a ^b Holleman, A. F.; Wiberg, E. (2001). Inorganic Chemistry. San Diego: Academic Press. ISBN 0-12-352651-5.
^ ^a ^b Riedel, Erwin; Janiak, Christoph (2007). Anorganische Chemie (7th ed.). Walter de Gruyter. p. 393. ISBN 978-3-11-018903-2.
^ ^a ^b ^c ^d Chandra, Sulekh (2004). Comprehensive Inorganic Chemistry. New Age International. p. 308. ISBN 81-224-1512-1.
^ Peterson, W.; Holloway, H.; Coyle, A.; Williams, M. (September 1971). "Antiprismatic Coordination about Xenon: the Structure of Nitrosonium Octafluoroxenate(VI)". Science. 173 (4003): 1238–1239. Bibcode:1971Sci...173.1238P. doi:10.1126/science.173.4003.1238. ISSN 0036-8075. PMID 17775218. S2CID 22384146.
^ "Xenon". Encyclopædia Britannica. Encyclopædia Britannica Inc. 1995.
^ Cotton (2007). Advanced Inorganic Chemistry (6th ed.). Wiley-India. p. 591. ISBN 978-81-265-1338-3.