Novel rare gas interstitial fullerenes of C₇₀

The formation and characterisation of the rare gas interstitial compounds of argon, krypton and xenon with C70 are presented. The materials were produced by hot-isostatically pressing (HIPing) powdered samples of C₇₀ at a temperature of 400°C and under a surrounding rare gas pressure between 170 and 200 MPa for ∼ 12 h. The materials were analysed by thermogravimetric analysis (TGA) and X-ray powder diffraction (XRD). It appears that under the HIP conditions used we were able to saturate all octahedral sites of the C₇₀ lattice (experimental error 5-10%), giving the rare gas stoichiometric materials Ar₁C₇₀, Kr₁C₇₀ and Xe₁C₇₀. The C₇₀ rare gas fullerenes were found to be more susceptible to loss of rare gas, compared with the corresponding C₆₀ materials, although the relative stabilities followed the same pattern, with heavier intercalated rare gases being lost more slowly. The argon is lost very easily (within a few days) whereas the krypton and xenon C₇₀ fullerenes were found to be stable at room temperature for several months, with some loss from the krypton fullerene.