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[2]
Thermochemistry
Std enthalpy of formation ΔfHo298	+153.5 kcal mol−1 [3]
Standard molar entropy So298	? J.K−1.mol−1
Hazards
EU classification	Explosive (E)
Related compounds
Related compounds	Perxenic acid Xenon trioxide
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Infobox references

Xenon tetroxide is a chemical compound of xenon and oxygen with molecular formula XeO₄, remarkable for being a relatively stable compound of a noble gas. It is a yellow crystalline solid that is stable below −35.9 °C; above that temperature it is very prone to explode, decomposing into xenon and oxygen (O₂).^[4][5]

All eight valence shell electrons of xenon are involved in the bonds with the oxygen, and the oxidation state of the xenon atom is +8. Oxygen is the only element that can bring xenon up to its highest oxidation state; even fluorine can only give XeF₆.

Reactions

At temperatures above −35.9 °C, xenon tetroxide is very prone to explosion, decomposing into xenon gas and oxygen 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 spectrometry.

Synthesis

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

2 XeO₄^2– → XeO₆^4– + Xe + O₂

The other is oxidation of the xenates with ozone in basic solution:

XeO₄^2– + O₃ + 2 OH^– → XeO₆^4– + O₂ + H₂O

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

Ba₂XeO₆ + 2 H₂SO₄ → 2 BaSO₄ + H₄XeO₆

H₄XeO₆ → 2 H₂O + XeO₄

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

2 H₄XeO₆ → O₂ + 2 H₂XeO₄ + 2 H₂O

References

1. ^ G. Gundersen, K. Hedberg, J. L.Huston (1970). "Molecular Structure of Xenon Tetroxide, XeO₄". J. Chem. Phys. 52 (2): 812–815. doi:10.1063/1.1673060. 
2. ^ Lide, David R. (1998). Handbook of Chemistry and Physics (87 ed.). Boca Raton, FL: CRC Press. pp. 494. ISBN 0-8493-0594-2 
3. ^ Gunn, S. R. (May 1965). "The Heat of Formation of Xenon Tetroxide". Journal of the American Chemical Society 87 (10): 2290–2291. doi:10.1021/ja01088a038.  edit
4. ^ H.Selig , J. G. Malm , H. H. Claassen , C. L. Chernick , J. L. Huston (1964). "Xenon tetroxide -Preparation + Some Properties". Science 143 (3612): 1322–3. doi:10.1126/science.143.3612.1322. JSTOR 1713238. PMID 17799234. 
5. ^ J. L. Huston, M. H. Studier, E.N. Sloth (1964). "Xenon tetroxide - Mass Spectrum". Science 143 (3611): 1162–3. doi:10.1126/science.143.3611.1161-a. JSTOR 1712675. PMID 17833897. 

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