Higher fullerenes are fullerene molecules consisting of more than 70 carbon atoms. They are cage-like fused-ring structures made of hexagons and pentagons, with a carbon atom at the vertices of each polygon and a bond along each polygon edge.
Contents
Synthesis
In 1990, W. Krätchmer and D. R. Huffman's developed a simple and efficient method which boosted the fullerene research. In this technique, carbon soot is produced from two high-purity graphite electrodes by igniting an arc discharge between them in an inert atmosphere (helium gas). Alternatively, soot is produced by laser ablation of graphite or pyrolysis of aromatic hydrocarbons. Fullerenes are extracted from the soot by dissolving it in appropriate organic solvents followed by chromatography. Milligram amounts of higher fullerenes can be obtained with this method in the laboratory and are available commercially for C76, C78 and C84.
Molecule
In the table, Nis represents the number of possible isomers within the "isolated pentagon rule", which states that two pentagons in a fullerene should not share edges. Symmetry is specified for the most experimentally abundant form(s), and * marks symmetries with more than one chiral form.
Solid
When C76 or C82 crystals are grown from toluene solution they have a monoclinic symmetry. The crystal structure contains toluene molecules packed between the spheres of the fullerene. However, evaporation of the solvent from C76 transforms it into a face-centered cubic form. Both monoclinic and face-centered cubic (fcc) phases are known for better-characterized C60 and C70 fullerenes.