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Xenon tetroxide

Xenon tetroxide


IUPAC name	xenon tetraoxide xenon(VIII) oxide
Structure
Molecular shape	Tetrahedral^[1]
Dipole moment	0 D
Properties
Molecular formula	XeO₄
Molar mass	195.29 g mol⁻¹
Appearance	Yellow solid below −36°C
Density	? g cm⁻³, solid
Melting point	−35.9 °C
Boiling point	0 °C decomp.^{[citation needed]}
Solubility in water	Soluble
Thermochemistry
Std enthalpy of formation Δ_fH^o₂₉₈	? kJ mol⁻¹
Standard molar entropy S^o₂₉₈	? J.K⁻¹.mol⁻¹
Hazards
EU classification	Explosive (E)
Related Compounds
Related compounds	Perxenic acid Xenon trioxide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Xenon tetroxide (molecular formula XeO₄) is a yellow crystalline solid that is stable below −35.9 °C.^[2]^[3] The xenon atom has an oxidation state of +8 and oxygen of −2. All eight valence shell electrons of xenon are involved, making it an unstable compound. Above -35.9°C, however, it explodes to give xenon and oxygen gas. Oxygen is the only element that can bring xenon up to its highest oxidation state; even fluorine can only give XeF₆, probably for steric reasons. Xenon tetroxide dissolves in water^{[citation needed]} to give perxenic acid, and in alkalis^{[citation needed]} to give the perxenate ion.

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Another known oxide is xenon trioxide. The dioxide remains elusive and only the XeOO⁺ cation has been identified by infrared spectroscopy in solid argon^[4].

Reactions

A spontaneous explosion occurs at temperature above −35.9 °C , with ΔH = 643 kJ/mol.

XeO₄ → Xe + 2 O₂

The two other short lived xenon compounds with an oxidation state of +8 are accessible by the reaction of xenon tetroxide with xenon hexafluoride. XeO₃F₂ and XeO₂F₄ can be detected with mass spectroscopy.

Synthesis

All syntheses start from the perxenates, which are accessible from the xenates through two methods. One is disproportionation of xenates to perxenates and xenon:

2 XeO₄²⁻ → XeO₆⁴⁻ + Xe + O₂.

The other is oxidation of the xenates with ozone:

2 XeO₄²⁻ + 4 e^{- + 2 O₃ → 2 XeO₆^4- + 2 O₂.}

Barium perxenate is reacted with sulfuric acid and the unstable perxenic acid is dehydrated to give xenon tetroxide:

Ba₂XeO₆ + 2 H₂SO₄ → 2 BaSO₄ + (H₄XeO₆ → 2 H₂O + XeO₄).

The unstable perxenic acid slowly undergoes a disproportionation reaction to the xenic acid and oxygen:

H₄XeO₆ → 1/2 O₂ + H₂XeO₄ + H₂O.

References

^ G. Gundersen, K. Hedberg, J. L.Huston (1970). "Molecular Structure of Xenon Tetroxide, XeO₄". J. Chem. Phys. 52: 812-815. doi:10.1063/1.1673060.
^ H.Selig , J. G. Malm , H. H. Claassen , C. L. Chernick , J. L. Huston (1964). "Xenon tetroxide -Preparation + Some Properties". Science 143: 1322.
^ J. L. Huston, M. H. Studier, E.N. Sloth (1964). "Xenon tetroxide - Mass Spectrum". Science 143: 1162.
^ M. Zhou, Y. Zhao, Y. Gong, J. Li (2006). "Formation and Characterization of the XeOO⁺ Cation in Solid Argon". J. Am. Chem. Soc. 128: 2504-2505. doi:10.1021/ja055650n.

Lide, D. R. (Ed.) (2002). CRC Handbook of Chemistry and Physics (83rd Edn.). Boca Raton (FL):CRC Press. ISBN 0-8493-0483-0.

Categories: Xenon compounds | Inorganic compounds | Oxides

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Xenon_tetroxide". A list of authors is available in Wikipedia.