Cymric wrote:
Indeed impressive, although I consider the fact of using a temperature well below minus 200 degrees centigrades a sort-of-a-cheat. Heat the substance to room temperatures and it will most likely dissociate into ethyne and krypton again.
Without doubt. I expect dissociation would occur well below even liquid nitrogen temperatures.
Whilst I was doing my degree, noble gas chemistry was a bit of a side fascination of mine. Before quantum mechanics totally revolutionised the understanding of the chemical bond, comnpounds of any such element were deemed fundamentally impossible, due to the belief that the atom had already had a perfectly stable electronic configuration.
As it goes, the evidence that you could create compounds of the heaver atoms in the series has been around a long time before anybody managed to do so. The notion of an "expanded shell" had been around a long time to explain the electronic configuration for interhalides, oxyanions etc. Nobody ever succeded in attempts to make such compounds directly, however.
It all kicked of in about 1963 IIRC, when a feller called Neil Bartlett discovered a very unusual reaction between molecular oxygen and platinum(VI) fluoride. The compound he got appeared to be PtF6O2, which would indicate a stupidly high oxidation state, even if the oxygen was a superoxide anion.
When he studied it, he actually found he'd created a dioxygen cation compund, (O2)+ (PtF6)-. This is not as unusual as it sounds, since as anybody who has studied molecular orbital bonding theory knows, the highest electrons in the O2 exist unpaired in antibonding orbitals. Removing one actually increases the bonding order from 2 to 2.5.
He then realised that the size and first ionization potential of O2 and Xe were very similar, so he just tried it and managed to repeat the reaction to get what he believed was XePtF6 (in fact it was a mixture of xenon oxidation states).
A flurry of activity followed and it was discovered that direct flouination of Xenon was possible, up to the hexaflouride (high temperature and pressure needed for that one). XeF2 can be made by from exposing a mixture of fluorine and xenon in a sealed glass tube to sunlight.
The flourides can be hydrolysed to oxides and oxyanions. Stabilised perxennate salts are even available for quantitative analysis.
Since then, many compounds of xenon have been prepared and the Xe-C and Xe-N, Xe-H and Xe-D bonds are known.
Krypton, on the other hand is an order of magnitude less reactive, which makes this find even more remarkable.
The stability of these bonds is predicted by advanced molecular orbital calculations (known as "ab initio") and preparing the compound is proof to support the molecular orbital model.
The same team also managed to prepare the only known argon compound, Argon Hydrofluoride (HArF) in a similar manner.
As for a teflon substitute, no chance. Even Xe-C bonds dissociate rapidly at ambient temperatures. You do *not* need that form of carbon radical floating around when there is oxygen and stuff present ;-)
