An elusive wreath of carbon has made its long-awaited debut.
Scientists created a molecule called cyclocarbon and imaged its structure, describing the ring of 18 carbon atoms online August 15 in Science. The work unveils a new face of one of chemistry’s most celebrated elements.
“It’s not every day that you make a new form of carbon,” says chemist Rik Tykwinski of the University of Alberta in Edmonton, Canada, who was not involved with the research. The result had eluded chemists for so long that Tykwinski had placed a bet about whether cyclocarbon would be created and imaged. “I basically won a bottle of Scotch from a friend,” he says.
Cyclocarbon joins other forms of the versatile element, including diamond, graphite, thin sheets called graphene, tiny spheres known as buckyballs and miniature cylinders called carbon nanotubes.
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Chemists thought that it should be possible to create the ring-shaped molecules of carbon. But until now, nobody knew what their properties would be, says physicist Katharina Kaiser of IBM Research in Zurich. “It’s really amazing that we found it and it’s absolutely great that we could characterize it.”
In the lab, Kaiser and colleagues started with molecules of cyclocarbon oxide, which consist of carbon atoms arranged in a loop with additional carbon monoxide groups attached to the atoms. Removing the carbon monoxide to create the coveted new form of carbon is no easy task; those groups help to stabilize the molecule. Using an atomic force microscope, the researchers managed to pluck off the extraneous carbon monoxide by applying voltages to the molecule.
Eventually, the procedure yielded a bare ring of carbon, which the team imaged with the microscope. Cyclocarbon reacts easily with other substances, so to isolate it, the team created the new carbon molecule on an inert surface of table salt.
Previous research had found hints of cyclocarbon molecules in a gas. But that work didn’t satisfy chemists’ curiosity because it wasn’t possible to image the molecule and confirm its structure. In particular, it was unclear if the bonds between each atom would alternate between longer and shorter lengths, known as single and triple bonds, or whether all the bonds would be the same length, or double bonds. The new study resolves the debate, revealing that the carbon atoms are held together by alternating single and triple bonds.
That conclusion could help scientists refine the complex computer calculations that are used to predict the structures of unknown molecules. “There’s still a big question whether many of these … calculations give the right answer, so it’s very important to confirm by experiment,” says chemist Yves Rubin of UCLA, who was not involved with the study.
Previous work on new forms of carbon has been received with great excitement. The discovery in the 1980s of buckyballs and the family of molecules that includes them, fullerenes, garnered a Nobel Prize and much additional research (SN: 10/19/96, p. 247). Likewise, the 2004 discovery of graphene was honored with a Nobel and followed by investigations of potential applications in electronics, for example (SN Online: 10/5/10).
But because cyclocarbon isn’t stable, it can’t be bottled up for further study. So, for now, it’s not clear how wide-ranging the new molecule’s impact will be.