Noble gases clathrate compounds

As with other compounds, solution effects can elevate the condensation temperatures of clathrate guest species. Sill and Wilkening calculated that in a gas of solar composition the major clathrate, and the first to form, will be ice-methane, and that noble gases can substitute for the methane at temperatures higher than decomposition temperatures for noble gas clathrates. They calculate, for example, that in a total nebular pressure of 2 x 10 atm (high in comparison with most model pressures currently considered of about 10 4 atm ), ice-methane clathrate at 80 K will have dissolved 99% of the available Xe (and substantially smaller amounts of the other noble gases). 

What about neutral helium-containing compounds Atomic helium has been trapped inside dodecahedrane and buckminsterfullerene, analogous to other endohe-dral species to be discussed later. Are the resulting species C2oH2oHe and CeoHe organohelium compounds, or are they better understood as related to the long-known noble gas clathrates ... 

Strictly speaking, the title noble-gas chemistry should be an oxymoron. But the noble gases are not literally and completely noble in the sense that they fail entirely to interact chemically with other forms of matter. Under appropriate conditions in the laboratory they can form real compounds with other elements, although there is no evidence that actual noble-gas compounds are relevant in cosmochemistry (possibly excepting ice clathrates in comets). StiU, planetary materials do contain noble gases that were somehow incorporated into them, and at least some of these appear to have involved some form of chemical interaction. The issue of chemical interactions is a venerable topic in noble-gas cosmochemistry, but there are still questions that have been unanswered for a long time. 

Until 1962 only physical inclusion compounds were known. Argon, krypton, and xenon form cage or clathrate compounds with water (clathrate hydrates) and with some organics such as quinol. The host molecules are arranged in such a way that they form cavities that can physically trap the noble gas atoms, referred to as guests. The noble gas will be released upon dissolution or melting of the host lattice. 

Chemically, radon is a noble gas. As such, it is colorless, odorless, and almost chemically inert. Although radon is not chemically active, it is interesting to note that radon is not a totally inert gas either. Studies on radon chemistry have been reported in which compounds such as clathrates and complex fluorides have been formed. Compared with the other noble gases, radon is the heaviest and has the highest melting point, boiling point, critical temperature, and critical pressure. 

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