Noble gas compounds

Noble gas compounds are chemical compounds that contain at least one noble gas atom . Noble gases have a closed valence shell and thus no tendency to form compounds. Nevertheless, there are compounds of some noble gases. However, these tend to decay relatively quickly, and very many of them are only stable at low temperatures. They are therefore also very strong oxidizing agents .

Until 2017, noble gas compounds were only known from the four heavy noble gases argon , krypton , xenon and radon , but not from helium and neon . So-called inclusion compounds or clathrates , in which the noble gas atoms are only weakly bound, are not noble gas compounds in the sense of this article .

stability

With the light noble gases helium and neon, the first ionization energies are very high. So far it has not been possible to achieve their ionization by chemical methods, because there is no oxidizing agent that would be capable of such a reaction.

With the heavier homologues, the ionization energy decreases with increasing atomic number , so that stable compounds can be formed from them. That is why there are noble gas compounds almost exclusively from the noble gases argon to radon. From the oganesson (element 118), which was added in 2006 , only three atoms were produced, the chemical properties of which are still unknown.

The stability of radon compounds is also limited because this element is radioactive and even the longest-lived isotope ²²² Rn only has a short half-life of less than 4 days.

Important connections

Are from the element krypton far only the compounds krypton difluoride KrF ₂ (after reaction with Lewis acid MF _n as KrF ⁺ the strongest known oxidants) and the stable only at low temperatures Kryptonbis (pentafluororthotellurat) Kr (OTeF ₅ ) ₂ known.

Most of the compounds are known from xenon. In xenon compounds the xenon has the oxidation states +2, +4, +6 or +8. As xenon compounds are fluorides , oxides , and also xenon nitrogen compounds, Xenon-carbon compounds and complex compounds (for example XePtF ₆ known).

Fluoride

There are three known simple xenon-fluorine compounds:

Xenon difluoride XeF ₂ , xenon tetrafluoride XeF ₄ and xenon hexafluoride XeF ₆ .

Xenon difluoride and xenon tetrafluoride have a linear or square-planar structure according to the VSEPR model . They appear monomeric. Xenon hexafluoride has a square-bipyramidal (distorted octahedral) structure.

All xenon fluorides are produced by thermal or photochemical activation of xenon / fluorine mixtures. Which product is created depends on the molar ratio and the reaction conditions - pressure, temperature.

→ see also: Excimer laser (unstable: F ₂ , Xe, ArF, KrF, XeBr, XeCl, XeF)

Oxides

Xenon (VI) oxide XeO ₃ and xenon (VIII) oxide XeO _{4 are} known as oxides . Both oxides are very unstable and explosive, they are strong oxidizing agents. According to the VSEPR model, the structure of xenon trioxide is trigonal-pyramidal (pseudo-tetrahedral), that of xenon tetrahedral is tetrahedral.

→ Representation of the trioxide by complete hydrolysis of xenon hexafluoride:

${\displaystyle \mathrm {XeF_{6}+3\ H_{2}O\longrightarrow XeO_{3}+6\ HF} }$

Helium compounds

Na ₂ He could be produced in a diamond high pressure cell and is only stable at a very high pressure of> 113 G Pa . In February 2017 the compound Na ₂ HeO was predicted, which should be stable at> 15 GPa. A helium compound was computationally developed and represented, and a second was predicted.

More connections

• The first xenon compound produced was xenon hexafluoroplatinate XePtF ₆ in 1962.

• The first xenon-metal compound produced is a tetra-xenon-gold (II) cation, which has an exactly square-planar structure. It was synthesized by Stefan Seidel and Prof. Konrad Seppelt from the Institute for Inorganic and Analytical Chemistry at the Free University of Berlin .

• A xenon-nitrogen compound was first presented by DesMarteau in 1974:

${\displaystyle \mathrm {2\ XeF_{2}+2\ HN(SO_{2}F)_{2}{\xrightarrow {(CH_{2}Cl_{2};\ 273\ K;\ 4\ Tage)}}\ 2\ FXeN(SO_{2}F)_{2}+2\ HF} }$

• The argon fluorohydride (HArF) was able in 2000 photolysis of hydrogen fluoride are synthesized in an argon matrix at 7.5 K. Proof was achieved using new lines in the infrared spectrum. The compound is only stable at temperatures below 27 K.

${\displaystyle \mathrm {HF+Ar\ {\xrightarrow {(7,5\ K;\ Photolyse)}}\ HArF} }$

swell

1. ↑ Section "The chemistry of noble gases" in: Huheey, E. Keiter, R. Keiter: Inorganic Chemistry, 2nd edition deGruyter, Berlin - New York 1995
2. ↑ Xiao Dong, Artem R. Oganov et al. a .: A stable compound of helium and sodium at high pressure. In: Nature Chemistry. 9, 2017, p. 440, doi : 10.1038 / nchem . 2716 .
3. ↑ N. Bartlett: Xenon Hexafluoroplatinate (V) Xe ⁺ [PtF ₆ ] ^- In: Proceedings of the Chemical Society 1962, p. 218
4. ↑ S. Seidel, K. Seppelt: Xenon as a Complex Ligand: The Tetra Xenono Gold (II) Cation in AuXe ₄ ²⁺ (Sb ₂ F ₁₁ ^- ) ₂ In: Science 2000, pp. 117-118
5. ↑ innovations-report: First xenon metal compound synthesized , 2001.
6. ↑ RD LeBlond, DD DesMarteau, Fluoro [imidobis (sulphuryl fluoride)] xenon. An example of a xenon nitrogen bond, J. Chem. Soc., Chem. Commun. , 1974 , 555-556. doi : 10.1039 / C39740000555
7. ^ Leonid Khriachtchev, Mika Pettersson, Nino Runeberg, Jan Lundell, Markku Räsänen: A stable argon compound. In: Nature. 2000, 406, pp. 874-876, doi : 10.1038 / 35022551 .

literature

• M.Binnewies: General and Inorganic Chemistry Spectrum Verlag, Heidelberg 2004 ISBN 3-8274-0208-5
• W. Grochala, Atypical compounds of gases which have been called 'noble', Chem. Soc., Rev. 36 2007 , 1632-1655, doi : 10.1039 / B702109G