A New Chemistry for Carbon

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A New Chemistry for Carbon

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The perfectly round C60 "buckyball" cluster. Source: National Science Foundation

A NEW CHEMISTRY FOR CARBON

Until a few years ago, there were two known forms of pure carbon, graphite and diamond. Then an improbable-seeming third form of carbon was discovered: a hollow cluster of 60 carbon atoms shaped like a soccer ball. Buckminsterfullerene or "buckyballs"--named for the American architect R. Buckminster Fuller, whose geodesic domes had a similar structure--is the roundest, most symmetrical large molecule known. It is exceedingly rugged and very stable, capable of surviving the temperature extremes of outer space.

At first, however, the molecule was a mystery wrapped in an enigma. But when a convenient way of making this molecule, also known as C60, was discovered, it set off an explosion of research among chemists, physicists, and materials scientists to uncover the molecule's secrets. Investigators soon discovered a whole family of related molecules, including C70, C84 and other "fullerenes"--clusters as small as C28 and as large as a postulated C240.

These unusual molecules turn out to have extraordinary chemical and physical properties.They react with elements from across the periodic table and with the chemical species known as free radicals--key to the polymerization processes widely used in industry--thus opening up the fullerenes to the manipulative magic of organic chemists. When a fullerene is "doped" by inserting just the right amount of potassium or cesium into empty spaces within the crystal, it becomes a superconductor--the best organic superconductor known. More important, because C60 is a relatively simple system, it may help physicists master the still mysterious theory of high-temperature superconductivity.

Speculation and some hard work on potential applications began almost immediately after the discovery of buckyballs. Possible applications of interest to industry include optical devices; chemical sensors and chemical separation devices; production of diamonds and carbides as cutting tools or hardening agents; batteries and other electrochemical applications, including hydrogen storage media; drug delivery systems and other medical applications; polymers, such as new plastics; and catalysts.

Catalysts, in fact, appear to be a natural application for fullerenes, given their combination of rugged structure and high reactivity. Experiments suggest that fullerenes which incorporate alkali metals possess catalytic properties resembling those of platinum. The C60 molecule can also absorb large numbers of hydrogen atoms--almost one hydrogen for each carbon--without disrupting the buckyball structure. This property suggests that fullerenes may be a better storage medium for hydrogen than metal hydrides, the best current material, and hence possibly a key factor in the development of new batteries and even of non-polluting automobiles based on fuel cells. A thin layer of the C70 fullerene, when deposited on a silicon chip, seems to provide a vastly improved template for growing thin films of diamond.

It is too early to make reliable forecasts of commercial potential, although the early indications are that buckyballs may represent a technological bonanza when their properties are fully understood. Yet it is important to note that the discovery of this curious molecule and its cousins was serendipitous, made in the course of fundamental experiments aimed at understanding how long-chain molecules are formed in outer space. It is a strong reminder that fundamental science is often the wellspring of advanced technology in ways that are completely unpredictable.