C₃₆, a new carbon solid

Under appropriate non-equilibrium growth conditions, carbon atoms form relatively stable hollow dusters of well-defined mass number, collectively known as fullerenes. The mass production, purification and condensation of such dusters into a molecular solid is generally essential to full experimental characterization: the initial discovery of C₆₀ for example, had to await a bulk synthesis method₃ six years later before detailed characterization of the molecule was possible. Gas-phase experiments have indicated the existence of a wide range of fullerene clusters, but beyond C₆₀ only a few pure fullerene solids have been obtained most notably C₇₀. Low-mass fullerenes axe of particular interest because their high curvature and increased strain energy owing to adjacent pentagonal rings could lead to solids with unusual intermolecular bonding and electronic properties. Here we report the synthesis of the solid form of C₃₆ by the arc-discharge method. We have developed purification methods that separate C₃₆ from amorphous carbon and other fullerenes, to yield saturated solutions, thin films and polycrystalline powders of the pure solid form. Solid-state NMR measurements suggest that the molecule has D(6h) symmetry, and electron-diffraction patterns are consistent with a tightly bound molecular solid with an intermolecular spacing of 6.68 Å. We observe large increases in the electrical conductivity of the solid on doping with alkali metals.