Rare-Gas Intercalation Into Fullerene Interstices

We review our neutron diffraction studies of the intercalation of the rare gases into the interstices of C-60 at pressures ranging from 0 to 6 kbar, primarily at room temperature, but also at other temperatures. Room temperature compressibilities of C-60 for both the face-centered-cubic and simple-cubic phases using Ar, which does not intercalate, as the pressure medium are in excellent agreement with the earlier work of David et al., while the values for He and Ne are slightly smaller than those using Ar. The rates of intercalation and release of Ne, at a number of different temperatures, have been measured and show that, at a given temperature, intercalation is much slower than release. Structural refinements of the Ne intercalated C-60 have been carried out for room temperature samples at many different pressures. These data suggest that Ne only intercalates into the octahedral hole and that the occupancy increases smoothly with pressure.