Buckminsterfullerene: The Soccer-Ball Molecule Found by Accident
On November 14, 1985, the journal Nature published a two-page letter claiming something almost no chemist expected: a third form of pure carbon, after diamond and graphite, made of 60 atoms joined into a hollow ball. The team named it after an architect famous for his geodesic domes. Buckminsterfullerene, or C60, was found by accident while its discoverers were chasing molecules from distant stars, and its shape was cracked late at night with paper, tape and a beer.
A chemist chasing carbon from the stars
The story begins with astronomy. Harry Kroto, a chemist at the University of Sussex in England, had helped discover long, chain-like carbon molecules in interstellar space. According to the American Chemical Society’s history of the discovery, he was convinced they formed in the atmospheres of carbon-rich red giant stars, and he wanted to prove it in the lab.
The instrument he needed was in Texas. At Rice University, Richard Smalley had built a laser-supersonic cluster beam apparatus, nicknamed AP2, that could vaporize almost any material and study the clusters of atoms that formed as the vapor cooled. The Nobel Foundation’s 1996 press release describes the method: an intense laser pulse vaporizes a carbon surface, the freed atoms are swept along in a stream of helium and clump into clusters, and the clusters are cooled in a vacuum and weighed by mass spectrometry.
Kroto learned about the machine from Robert Curl, an old friend and Smalley’s collaborator, at a conference in Austin in 1984. Smalley wasn’t keen at first. The ACS history says he and Curl were busy with semiconductor clusters. A team at Exxon had already vaporized graphite in a similar machine and found that carbon clusters larger than about 40 atoms tended to have an even number of atoms. A year later Smalley relented, and Kroto arrived in Houston in late August 1985.
The peak at sixty
The experiments began in earnest on September 1, 1985, with graduate students James Heath, Sean O’Brien and Yuan Liu running the machine. The ACS history describes about ten feverish days of work. On Wednesday, September 4, with helium as the carrier gas, the students saw a striking peak at exactly 60 carbon atoms, with a smaller one at 70. Liu wrote in the lab book, “C60 and C70 are very strong,” underlined and with an exclamation mark.
By tuning the conditions, the team could make C60 dominate. In one run, according to the ACS, the machine produced forty times more C60 than C58 or C62. The molecule was also strangely unreactive. That suggested it had no “dangling bonds,” the loose ends at the edges of ordinary carbon molecules that are usually capped with hydrogen. At first the team half-jokingly called it a “wadge,” British slang for a handful of stuff.
How buckminsterfullerene got its shape
The puzzle was what shape could have 60 carbon atoms and no edges. A closed cage would have no dangling bonds. The team kept returning to the geodesic domes of the American architect R. Buckminster Fuller, but they thought those domes were made only of hexagons. Curl doubted that hexagons alone could close into a ball.
Smalley, as the ACS tells it, tried modeling the shape on his home computer the night of Monday, September 9, and failed. So he cut hexagons out of a legal pad and taped them together, but even with some cheating they wouldn’t close. Around midnight he went to the kitchen for a beer and remembered Kroto describing a “stardome” he had once built for his children with pentagons as well as hexagons. Smalley cut a single pentagon and surrounded it with hexagons. “Now no cheating was required,” he later wrote. “The hexagons automatically assumed the shape of a bowl.”
The finished paper model had 12 pentagons and 20 hexagons. When Smalley phoned Bill Veech, chair of Rice’s mathematics department, to ask about the shape, the answer came back a few minutes later: “what you’ve got there, boys, is a soccer ball.”
The letter was sent to Nature on September 12, received on September 13, and published on November 14, 1985, according to the Nobel Foundation. Written by Kroto, Heath, O’Brien, Curl and Smalley, “C60: Buckminsterfullerene” proposed a truncated icosahedron: “a polygon with 60 vertices and 32 faces, 12 of which are pentagonal and 20 hexagonal.” With a carbon atom at each vertex, each atom forms two single bonds and one double bond, and the molecule “appears to be aromatic.” The name came from Fuller’s domes. Who thought of it is disputed. Curl later said, “Harry was convinced that was his idea and Rick was convinced it was his idea and I’m convinced it wasn’t my idea.”
Illustration: glowing gas around a pair of stars, the kind of environment where fullerenes have been detected.
Five years of doubt, then a pile of black powder
A peak in a mass spectrum is not a molecule in a bottle. The Nobel Foundation notes that the discovery had a mixed reception, with both criticism and enthusiasm, and the team spent 1985 to 1990 gathering more evidence. In one test, carbon was vaporized with a lanthanum salt, and the team detected C60 carrying a lanthanum atom that laser light couldn’t knock loose, as you’d expect if the metal was trapped inside the cage. In “shrink-wrapping” experiments, lasers stripped carbon atoms off metal-filled cages two at a time, until the cage was squeezed tight around the atom inside.
The decisive step came in 1990. Wolfgang Krätschmer of the Max Planck Institute for Nuclear Physics in Heidelberg and Donald Huffman of the University of Arizona, with students Konstantinos Fostiropoulos and Lowell Lamb, made C60 in bulk by running an electric arc between graphite rods in helium and extracting the soot with an organic solvent. Their paper in Nature described a new form of solid carbon, a “somewhat disordered hexagonal close packing of soccer-ball-shaped C60 molecules.” Infrared spectra and X-ray diffraction confirmed the predicted structure, and C70 was present at a few percent.
That opened the door. In 1996 Curl, Kroto and Smalley shared the Nobel Prize in Chemistry “for their discovery of fullerenes.” The family now includes C70, C76, C78, C84 and more. According to the ACS, the discovery also led to research on carbon nanotubes, the cylindrical cousins of buckyballs, and to new fields of advanced materials.
Buckyballs in space
The molecule that came out of a search for star chemistry turned out to be in space after all. In 2010 a team of astronomers reported in Science that the infrared spectrum of Tc 1, a planetary nebula, shows emission from cold, neutral C60 and C70. The two molecules make up a few percent of the carbon available there, which the authors read as a sign that “if the conditions are right, fullerenes can and do form efficiently in space.” In 2012 NASA’s Jet Propulsion Laboratory reported a Spitzer Space Telescope study that found buckyballs in solid form, stacked “like oranges in a crate,” around a pair of stars called XX Ophiuchi, about 6,500 light-years away.
Buckyballs also helped solve a much older astronomy puzzle. The diffuse interstellar bands are dark absorption lines in starlight, and for a long time none of the molecules behind them had been conclusively identified. In 2015 E. K. Campbell and colleagues at the University of Basel and Chemnitz University of Technology measured the spectrum of C60+, the positively charged ion, in the gas phase at 5.8 kelvin. They found bands at 9,632.7 and 9,577.5 ångströms, and their Nature paper concluded that these two interstellar bands come from C60+. According to the ACS, Kroto had also seen his 1985 carbon-chain experiment as a possible pilot for work on the carriers of the diffuse interstellar bands.
What’s known and what’s still open
C60‘s cage structure is settled. It was confirmed by bulk synthesis, infrared spectra and X-ray diffraction in 1990, and the Nobel Foundation describes the fullerene hypothesis as “completely confirmed.”
Practical uses came more slowly than the excitement. In 1996 the Nobel Foundation wrote that “no practically useful applications have yet been produced,” while pointing to superconducting salts, new polymers, catalysts and sensors as research directions. The ACS lists possible future uses in antibiotics and armor. Those are candidates, not established products, in these sources.
In space, the open questions are about chemistry: exactly how and where fullerenes form in space, and what molecules are behind the many diffuse interstellar bands that remain unidentified. Campbell’s identification covers two bands, not the rest.
Interested in other molecules built like cages and sandwiches? Odinity’s lab on synthesizing a cobalt cage complex traps a metal inside an organic cage, a chemical cousin of the metal-filled fullerenes. The ferrocene synthesis lab explores another unusually stable, symmetrical carbon compound. And the quantum dot nanocrystals experiment shows how materials behave at the nanoscale.