New class of compounds promises clean energy

By combining a common organic compound with a rare metal, a team of Brown University chemists has created a new class of molecules that have potentially important applications for the pharmaceutical, chemical and energy industries.

To create the mixture, scientists working in the laboratory of Dwight Sweigart, a Brown professor of chemistry, combined two compounds. One is hydroquinone, pale organic crystals critical for many biological processes as well as the manufacture of everything from skin bleaching creams to high-performance plastics. The other is the precious metal rhodium. The resulting reaction produced rhodium quinones.

"This mixture has marvellous properties," Sweigart said. "Rhodium quinones are very fast and efficient catalysts. They also have pores, or channels, that act like a sponge, giving them the ability to store gases. The secret is rhodium. It's the Superman of elements."

Rhodium is lighter than platinum, rarer than gold, and, at about $3,000 an ounce, the priciest of precious metals. The silvery white substance is prized as a potent, long-lasting catalyst and is used to concoct antifreeze, detergents and other industrial chemicals as well to make automotive catalytic converters, which cut down on air pollution. Rhodium is also the most reflective element on the periodic table and can be found in searchlights, dental mirrors, and giant microscopes known as synchotrons.

The potential applications of rhodium quinines include:

• Storage " Energy experts hope that hydrogen will eventually replace fossil fuels as a clean source of power. The promise: Convert the gas to electricity, leaving water as the only byproduct. But to create this 'hydrogen economy,' major hurdles must be overcome to make, transport and store hydrogen. Sweigart and his team have shown that rhodium quinones, in a solid state, feature channels suitable for storage of hydrogen and other gases, and might be used in fuel cells to generate electricity.
• Catalysis " Rhodium quinones are highly effective catalysts for so-called carbon-carbon coupling reactions. These reactions are essential to make drugs for cancer, depression and other diseases. Rhodium catalysts promise a conceptual advance over current production systems by boosting the amount of end product and by making new drugs possible. Sweigart is currently working with William Trenkle, an assistant professor of chemistry at Brown, and graduate student Julia Barkin to use the compounds to make drugs for asthma, depression and other conditions. Through Brown, the pair filed preliminary patents on the use of rhodium quinones as catalysts.

"After routinely working until 2 or 3 am in the lab, creating the new compound is extremely exciting," said Jeffrey Reingold, a graduate student working in the Sweigart lab. "The rhodium and the quinone parts of the molecule each contribute unique characteristics to generate a powerful new reagent with enormous potential. Much of our future research will focus on the development of this fascinating chemistry."