Rotor–stator molecular crystals of fullerenes with cubane

Abstract

Cubane¹(C₈H₈) and fullerene²(C₆₀) are famous cage molecules with shapes of platonic or archimedean solids. Their remarkable chemical and solid-state properties have induced great scientific interest^3,4,5. Both materials form polymorphic crystals of molecules with variable orientational ordering^6,7,8,9. The idea of intercalating fullerene with cubane was raised several years ago¹⁰ but no attempts at preparation have been reported. Here we show that C₆₀ and similarly C₇₀ form high-symmetry molecular crystals with cubane owing to topological molecular recognition between the convex surface of fullerenes and the concave cubane. Static cubane occupies the octahedral voids of the face-centred-cubic structures and acts as a bearing between the rotating fullerene molecules. The smooth contact of the rotor and stator molecules decreases significantly the temperature of orientational ordering. These materials have great topochemical importance: at elevated temperatures they transform to high-stability covalent derivatives although preserving their crystalline appearance. The size-dependent molecular recognition promises selective formation of related structures with higher fullerenes and/or substituted cubanes.