What Are Fullerenes?

Natural carbon can exist in several forms. Most people know about graphite and diamond, but there is a third type-- fullerenes. Sometimes these are mistakenly called a "new form of carbon"; in fact, fullerenes have been found to exist in interstellar dust as well as in geological formations on Earth. They are only new to us. Fullerenes are large carbon-cage molecules. By far the most common one is C₆₀-- also called a "buckyball"-- but some other relatively common ones are C₇₀, C₇₆, and C₈₄ (there are plenty of others too).

Fullerene cages are about 7-15 angstroms in diameter (that's around a billionth of a meter, or 6-10 times the diameter of a typical atom). In atomic terms, they are enormous-- a compound such as K₃C₆₀ looks like a stack of bowling balls (the C₆₀'s) with marbles poured between them. But fullerenes are still small compared to many organic molecules.

Chemically, they are quite stable; breaking the balls requires temperatures of over 1000 degrees C (the exact number depends on which particular fullerene). At much lower temperatures (a few hundred degrees C) fullerenes will "sublime," which means vapor will form directly from the solid. The balls don't break; they just separate from the solid intact. This property is used in growing crystals and thin films of fullerenes.

What is interesting about these "new" carbon materials? In pure scientific terms, fullerenes are fascinating because they show unusual properties for carbon materials. For example, adding 3 alkali atoms per C₆₀ results in a material which goes superconducting at quite a high temperature (10-40 K, depending which alkali). There are other organic superconductors, but they are different from A₃C₆₀. We still don't fully understand the electronic behavior of the alkali-C₆₀ compounds.

Also, having a molecule that looks like a cage invites the obvious question: can we put something in the cage? The answer is yes, as is discussed on the page about endohedral fullerenes.

What about practical applications? That's a tougher question. I discuss this on the page called What Are These Things Good For?.

In summary, fullerenes are fun because they are unusual. We are still exploring the physics, chemistry, and engineering potential of these materials. Although we've known about carbon as long as we've known about fire, we are still discovering new aspects of this element every decade. You can't say that about very many things.

Return to the Main Fullerene Page

Email: kimall (at symbol) mindspring.com