Credit: © 2008 NPG

Buckminsterfullerene is a highly symmetrical molecule, and its famous truncated icosahedral structure looks similar to a soccer ball, but with pentagons and hexagons of carbon. However, this is only one of 1812 potential isomers of C60, and the only one in which all the pentagons are isolated from each other. As a result of the stability of this and other fullerenes, the isolated-pentagon rule was suggested: the pentagons of carbon atoms in stable fullerenes are not connected. Although the existence of non-icosohedral C60 fullerenes has been suspected, it is only now that Su-Yuan Xie and colleagues at Xiamen University in China have been able to prepare, isolate and characterize two of them1.

Chlorinated species of the two lower-symmetry C60 compounds were made and isolated in low yields, but enough for detailed structural characterization. One of the compounds, C60Cl8, still had mirror symmetry (point group C2v), but the other one did not, making C60Cl12 chiral (Cs). The crucial structural feature, fused pentagon rings, is observed twice in the C2v compound and three times in the Cs cage. The chlorination stabilizes the structures, with the C2v-C60Cl8 compound calculated to be lower in energy than the corresponding octachloro derivative of icosahedral C60.

Xie and colleagues were able to perform a classical Freidel–Crafts reaction on one of the compounds, which resulted in it being substituted with four phenyl rings in quantitative yield. These were added only at hexagon–hexagon vertices, with the four Cl atoms at pentagon–pentagon joints remaining intact. The existence of the rule-breaking C60 compounds, together with the fact they can be functionalized at specific sites, offers the promise of creating a new range of functional fullerene materials.