Xenon hexafluoroplatinate

Xenon hexafluoroplatinate is the product of the reaction of platinum hexafluoride with xenon, in an experiment that proved the chemical reactivity of the noble gases. This experiment was performed by Neil Bartlett at the University of British Columbia, who formulated the product as "Xe⁺⁻", although subsequent work suggests that Bartlett's product was probably a salt mixture and did not in fact contain this specific salt.

Preparation

"Xenon hexafluoroplatinate" is prepared from xenon and platinum hexafluoride as gaseous solutions in SF₆. The reactants are combined at 77 K and slowly warmed to allow for a controlled reaction.

Structure

The material described originally as "xenon hexafluoroplatinate" is probably not Xe⁺⁻. The main problem with this formulation is "Xe⁺", which would be a radical and would dimerize or abstract a fluorine atom to give XeF⁺. Thus, Bartlett discovered that Xe undergoes chemical reactions, but the nature and purity of his initial mustard yellow product remains uncertain. Further work indicates that Bartlett's product probably also contained products of further oxidation by PtF₆, platinum derivatives PtF₅, ⁺⁻, and ⁺⁻. The title "compound" is a salt, consisting of an octahedral anionic fluoride complex of platinum and various xenon cations.
It has been proposed that the platinum fluoride forms a negatively charged polymeric anion with xenon fluoride cations. A preparation of "XePtF₆" by reaction of XeF₂ and PtF₄ in anhydrous HF solution results in a solid which has been characterized as a polymeric or oligomeric anion associated with XeF⁺. Such F-bridged polymeric chains and tetrameric ring with pendant XeF⁺ units have been observed in the crystal structures of the analogous compounds XeCrF₆ and XeMnF₆, respectively. These structures could serve as structural models for XePtF₆.

History

In 1962, Neil Bartlett discovered that a mixture of platinum hexafluoride gas and oxygen formed a red solid. The red solid turned out to be dioxygenyl hexafluoroplatinate, Bartlett noticed that the ionization energy for O₂ was very close to the ionization energy for Xe. He then asked his colleagues to give him some xenon "so that he could try out some reactions", whereupon he established that xenon indeed reacts with PtF₆. Although, as discussed above, the product was probably a mixture of several compounds, Bartlett's work was the first proof that compounds could be prepared from a noble gas. Since Bartlett's observation, many well-defined compounds of xenon have been reported including XeF₂, XeF₄, and XeF₆.