Buckyball scrambled

Chemists have rolled over one of the fundamental rules of fullerene chemistry - that two pentagons cannot be neighbors - to make an egg-shaped buckyball. Virginia Tech chemist Harry Dorn and colleagues were trying to make novel medical imaging contrast agents using novel fullerenes with terbium atoms trapped inside. They sent off their products to UC Davis for structure determination but graduate student Christine Beavers working with Alan Balch and Marilyn Olmstead was very surprised to obtain an X-ray structure showing that two carbon pentagons were fused in one of the compounds. This oddity meant that rather than a symmetrical buckyball, the compound was egg-shaped. The compound's formula Tb3N@C84 reveals that three Tb atoms are trapped in this oddity and somehow lead the material to break the rule.