Rotor–stator molecular crystals of fullerenes with cubane

Abstract

Cubane (C8H8) and fullerene (C60) are famous cage molecules with shapes of platonic or archimedean solids. Their remarkable chemical and solid-state properties have induced great scientific interest. Both materials form polymorphic crystals of molecules with variable orientational ordering. The idea of intercalating fullerene with cubane was raised several years ago 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.

Lattice dynamics of a rotor-stator molecular crystal: Fullerene-cubaneC60⋅C8H8

“…11, with a characteristic size in the platelet plane being of about 200 m͒, and a 200 mg powder. Cubane was synthesized by the method of Eaton.…”

“…17 C 60 ·C 8 H 8 cocrystals were prepared in the form of microcrystalline powder and monocrystals by the methods described in details in Ref. 11. It consists of dissolving a C 60 powder in toluene, and filtering it before adding excess amount of cubane to the solution.…”

“…In this paper, we present a study of the dynamics of a fullerene-cubane C 60 ·C 8 H 8 cocrystal, which was synthesized for the first time by Pekker et al 11 The interest of this model system stands in the complex molecular nature of the cocrystal, where molecules of icosahedral and cubic symmetries interact. The fcc unit cell of the disordered phase is represented in Fig.…”

“…Since its discovery, the structure of fullerene-cubane cocrystal has been extensively studied by Raman and infrared spectroscopies, 12,13 1 H-nuclear magnetic resonance, 14 x-ray diffraction and calorimetry, 11,15 which allowed to produce the pressure-temperature ͑P , T͒ "reaction map" of this crystal. 13 These studies showed that fullerene-cubane polymerizes into a very stable covalent derivative in which decomposed cubanes form covalent bonds with adjacent fullerenes 13,16 above 500 K.…”

“…The low-temperature phase was indexed as orthorhombic 11 but its space group, requiring the knowledge of the fullerene orientations, is still unknown.…”