HOLEY FULLERENE OPENS WIDE FOR H2
Open-cage derivative is first to provide H2-encapsulated complex in 100% yield
Japanese chemists for the first time have prepared an open-cage fullerene derivative with an orifice large enough to allow a hydrogen molecule to be inserted into the cage in 100% yield [J. Am. Chem. Soc., 125, 7152 (2003)].
"I think it is an important advance for this field, since I can see this type of system being used for H2 storage once C60 becomes cheaper," comments Yves Rubin, a chemistry professor at the University of California, Los Angeles.
Scientists are looking for efficient methods for stuffing fullerene cages with metal atoms or gases to make new types of functional materials.
Two years ago, Rubin and his collaborators at UCLA and Yale University reported the synthesis of a fullerene derivative featuring a "mouth" large enough to accept and trap a H2 molecule in 5% yield (C&EN, April 23, 2001, page 11). Although the yield has since been improved to 10%, this system still cannot compete with the new Japanese molecule, which Rubin says is better because it has a slightly larger orifice.
The new molecule was prepared from C60 in three steps in 40% overall yield by chemistry professor Koichi Komatsu and coworkers Yasujiro Murata and Michihisa Murata at Kyoto University. When they expose the compound to hydrogen gas at 800 atm and 200 °C in an autoclave, 100% encapsulation is achieved within eight hours, they report.
None of the encapsulated hydrogen escaped when a solution of the endohedral complex was monitored for more than three months at room temperature. However, hydrogen was released slowly when the solution was heated above 160 °C, Komatsu says.
During mass spectral studies, the Kyoto group discovered that laser irradiation can cause the endohedral complex to regenerate pristine buckminsterfullerene with H2 inside--that is, H2@C60--in the gas phase. This suggests that endohedral fullerene complexes might one day be prepared entirely by organic synthesis, Komatsu tells C&EN. In fact, his group is now aiming to close the orifice chemically to achieve a chemical synthesis of H2@C60.
|NANOCONTAINER The open-cage fullerene shown at right is filled with a H2 molecule. In the representation at left, the cage is empty.
IMAGES COURTESY OF KOICHI KOMATSU