Baby buckyballs hold unusual promise

19:00 29 April 2004, NewScientist.com news service

Miniature "buckyballs" have been created for the first time, and hold the promise of new and unusual physical properties for nano-engineers to explore.

Buckminsterfullerenes - buckyballs - are molecular spheres in which carbon atoms form interlinked pentagons and hexagons that resemble the panels on a soccer ball. Buckyballs, and the related carbon nanotubes, are extremely strong and very good conductors of electricity. This had led then to be common components of nanodevices such as tiny soldering irons and thermometers.

The molecules consist of 50 carbon atoms surrounded by 10 chlorine atoms (Image: Science)

Normally it takes 60 carbon atoms to construct a stable buckyball. But Su-Yuan Xie, from Xiamen University in south-east China, and colleagues made buckyballs from just 50 carbon atoms, by using a ring of 10 chlorine atoms as a belt to support the smaller structure.

Other fullerenes with fewer than 60 carbon atoms have been created before, but none that so closely resembles the original buckyball.

Isolated pentagons

A remarkable feature of the new buckyballs is that they do not obey the "isolated pentagon rule". This mathematical law states that a structure will fall apart if the edges of two of its pentagon sides touch. The new molecules defy this thanks to the support of the chlorine atoms.

Buckyballs and nanotubes are usually fabricated using an electric arc to vaporise carbon. The Chinese team used this method but added chlorine. They believe similar methods could be used to construct even smaller fullerene structures.

"Our successful capture of C[50] not only brings into reality a long-sought member of the fullerene family but also reveals that small fullerenes can be obtained in macroscopic quantities," the researchers write in the journal Science.

Electronic properties

Laszlo Mihaly, a buckyball researcher Stony Brook University in New York, US, says the molecules may turn out to have unusual conducting characteristics. This is because the carbon atoms should conduct electricity well, like a normal buckyball, but the chlorine ones should act as insulators.

He says it will therefore be interesting to experiment with the structures. "We do not have the capacity to predict the properties of such solids," he told New Scientist. "What happens if we take the C[50]Cl[10] and add a bit of sodium or rubidium? Nobody can tell for sure."

"It is an exciting piece of work," adds Kosmas Prassides, at the University of Sussex, UK. "There are very few experimental studies on small fullerenes, especially those not obeying the isolated pentagon rule."

Journal reference: Science (vol 304, p 699)