Buckyballs act just like giant atoms, complete with s, p and d orbitals that are bound to the sphere's hollow centre
Buckminsterfullerene (C60) is a famously spherical molecule, made up of sixty carbon atoms arranged in hexagons and pentagons. When doped with alkali metals such as lithium or potassium, the resulting phases offer metallic, magnetic or even superconducting properties. Studies of KxC60 on gold surfaces have revealed orientational ordering of C60 molecules — an effect attributed to anisotropic intermolecular interactions that are thought to arise from electron hopping between π-orbitals in molecular neighbours.
Investigating a similar system — with the fullerenes adsorbed on a copper surface — Hrvoje Petek and colleagues1 at the University of Pittsburgh have discovered atom-like orbitals on C60. These 'superatom molecular orbitals' (SAMOs), as the team calls them, were detected by performing distance–voltage scans using low-temperature scanning tunnelling microscopy. At energies 2–3 eV above the lowest unoccupied molecular orbital, giant versions of s, p and d orbitals seem to be present. Studying C60 dimers suggests that the superorbitals hybridize to form both bonding and antibonding σ and π molecular orbitals.
But how can 'atomic' orbitals exist without a positive nucleus? It is proposed that the curvature of the molecule results in a hybridization of molecular states that leads to the creation of a dipole normal to the surface — and hence an internal potential. Consequently, Petek and co-workers suggest that SAMOs could be a property of any rolled or wrapped two-dimensional material, such as nanotubes.
Feng, M., Zhao, J. & Petek, H. Atomlike, hollow-core-bound molecular orbitals of C60 . Science 320, 359–362 (2008). 10.1126/science.1155866
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Withers, N. Superatomic orbitals. Nature Chem (2008). https://doi.org/10.1038/nchem.4