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Structure of a New Family of Buckyballs Created

Illustration of what could be called Carbon 68 - image by Steve Stevenson.
Blacksburg - Dec 4, 2000
Virginia Tech chemists and colleagues at several institutions reported in the November 23, 2000 of Nature that they have created a family of fullerene molecules that break the sacrosanct isolated-pentagon rule ("A stable non-classical metallofullerene family").

Since the carbon clusters known as fullerenes, or buckyballs, were discovered in 1985, the only stable structure has consisted of even numbers of carbon atoms linking to form pentagons isolated from each other by hexagons to form a spherical cage.

Now, a team of researchers have created a fullerene with pentagons that share one side -- looking like an angular figure eight.

Virginia Tech chemistry professor Harry C. Dorn explains that the new molecule is possible because of an earlier discovery by the university's researchers, reported in Nature last year (Sept. 2, 1999).

The chemists discovered a way to put four metal atoms inside a fullerene of 80 carbon atoms (C80), creating endohedral metallofullerenes (metal inside buckyballs). The new structure has only 68 carbon atoms, which are stabilized by the three metal atoms.

The three metal atoms have a nitrogen atom core. "It is truly remarkable that a cage of only 68 carbon atoms can encapsulate a molecular cluster of four atoms," says Dorn.

"The filled C80 nanosphere has become an important material in nanotechnology devices being developed at the university," says Dorn. "Now, the linked pentagons will help us understand defects in fullerenes and nanotubes," explains Dorn.

"The metal atoms stabilize the defect. Our study of this new family of materials will help us understand where and when defects occur." He says the new molecule can also be used as new nano-material building blocks that incorporate a variety of other lanthanide metals, such as holmium, gadolinium, and erbium.

The Virginia Tech researchers discovered that they had created the rule-breaking metallofullerene when they conducted a detailed study of the same mixtures that yielded the first metallofullerenes.

In the spring of 1999, having already discovered that nitrogen will allow metal atoms to be inserted into fullerenes, post doctoral fellow Steve Stevenson (now at Luna Innovations) noticed an unexplained peak in the mass spectrometry of the metallofullerenes and isolated it for NMR analysis by Virginia Tech graduate Roy Bible (now at Searle).

NMR indicated the new structure, but that one source wasn't proof enough for publication. So Virginia Tech undergraduate student Greg Rice and Emory and Henry College visiting scholar Jim Duchamp were able to make about a half of a milligram of the material.

"We tried to get a crystal structure, but that hasn't worked yet," says Dorn. "So we contacted Patrick Fowler of the University of Exeter, who did a theoretical study. He used computer modeling to determine that of 6,332 ways to assemble fullerenes, only 11 structures agreed with our data, and only one structure was stable."

"This research was a beautiful blend of experimental data and theoretical data," says Dorn.

Once the structure had been identified, the experimentalists could prove they could isolate the new fullerene they had created, recreate it, and change it.

The first C68 cage contained scandium, which is used because it is easy to track with an NMR. The Virginia Tech researchers created a family of C68 endohedral metallofullerenes by inserting other metals. They are now able to create large, pure quantities of C68 with rare-earth atom clusters (A3N@C68).

Authors of the Nov. 23 article in Nature (A stable non-classical metallofullerene family) are Stevenson, Fowler, T. Heine of the Universita di Bologna, Duchamp, Rice, Virginia Tech analytical chemists Tom Glass and Kim Harich, Elizabeth Hajdu and Bible at Searle, and Dorn.

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