Playing ball with new carbon molecules.

The aesthetically pleasing shape of buckminsterfullerene--60 carbon atoms arranged in the pattern of a soccer ball--captured the imaginations of scientists everywhere when the molecule was first discovered in 1985. Now, two studies have isolated for the first time several members of the fullerene family, one smaller and the others larger than their famous cousin.

In the June 25 Nature, researchers from the University of California, Berkeley describe their discovery of carbon-36 ([C.sub.36]), the first fullerene smaller than the buckyball. In the June 18 Nature, scientists from TDA Research in Wheat Ridge, Colo., report success in extracting larger fullerenes, notably [C.sub.74] and [C.sub.80], from an indeterminate mix of carbon molecules. Previously, scientists had known that bigger fullerenes existed but didn't have a practical way to separate them.

Both studies may help researchers explore the properties of fullerenes in solid form. The larger fullerenes and [C.sub.36] readily fuse into polymer films. The strong bonds that form between molecules appear to give these solid films electronic and mechanical properties that differ from those of buckyball films.

The most common method of making fullerenes is by sparking two carbon rods together to produce a soot that contains a melange of fullerenes and other carbon compounds (SN: 10/13/90, p. 238). Unlike [C.sub.60] and [C.sub.70], neither [C.sub.36] nor the larger fullerenes are soluble in toluene, an organic solvent, so they cannot be extracted easily from the soot.

The Berkeley researchers, physicist Alex Zettl and his colleagues Charles R. Piskoti and Jeffery Yarger, used two novel methods to isolate [C.sub.36]. One technique produced a hard, black film and the other a fine powder. Using electron diffraction to examine the powder, they found evidence that the [C.sub.36] molecules bond strongly with each other.

The [C.sub.36] films seem to be more robust than films of [C.sub.60], surviving at high temperatures, says John H. Weaver of the University of Minnesota in Minneapolis.

Moreover, by adding sodium or potassium atoms to solid [C.sub.36], the researchers could lower the electrical resistance of the material, suggesting that, like [C.sub.60], it could become superconducting with some modification.

At TDA Research, John M. Alford and Michael D. Diener found a way to make the ordinarily insoluble fullerenes such as [C.sub.80] dissolve in an organic liquid. After removing the bulk of the [C.sub.60] and [C.sub.70], "we add electrons to the fullerenes electrochemically, which breaks the bonds" holding them together, says Alford. The resulting negatively charged molecules dissolve in benzonitrile, allowing the researchers to extract them.

"It's a very convincing demonstration of how to prepare things that we had thought were insoluble," says Weaver.

The electronic structure of the larger fullerenes allows them to polymerize more easily, says Alford. Although this makes them harder to work with than buckyballs, it also gives them some interesting and unusual properties. The same could be said for [C.sub.36]. The two groups are already exploring what those properties might be.