Fullerenes

Fullerenes, which were discovered in 1985 by Kroro, Curl and Smalley (and for which the Nobel prize was awarded in 1996). The archetypal fullerene C$_{60}$, also known as buckminsterfullerene, C$_{60}$ is composed entirely of carbon (no hydrogens), and each of the 60 carbon atoms is $sp^2$ hybridized. The molecule is also nearly perfectly spherical as shown in the picture below:

Figure: C$_{60}$ fullerene.

The pattern of carbon bonding is exactly the same as the pattern on the surface of a soccer ball. There are 20 hexagonal carbon rings and 12 pentagonal carbon rings. In order to accomodate this structure, some of the bond angles are distorted from the ideal 120$^{\circ}$ corresponding to $sp^2$ hybridization, with a value of 108$^{\circ}$. Combining the 60 $p_z$ orbitals gives MOs that are spread over the entire molecule.

Another type of fullerene is known as the carbon nanotube, which is obtained by taking a sheet of graphene (a single layer of carbon in the structure of graphite) and rolling it into a cylinder. Depending on how the sheet is rolled, carbon nanotubes can be either metallic or semiconducting. The picture below shows a graphene sheet and a typical carbon nanotube:

Figure: A graphene sheet and its rolled-up version into a carbon nanotube.

Some interesting uses of carbon nanotubes are as nanowires, which exploit their high conductivity, nanoropes, which exploit their high tensile strength, and confinement agents for molecular wires.

It has also been proposed that closed fullerenes, such as C$_{60}$ or carbon nanotubes capped at both ends (also known as nanohorns) could be used to encapsulate drug molecules. The fullerene could then be coated with protein so as to make it soluble and specific to a particular biological environment. In this way, such fullerenes could serve as drug-delivery agents. This proposal has yet to be realized in practice.