Angewandte Chemie International Edition
Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
For full article and contact information, see Angew. Chem. Int. Ed. 2001, 40 (8), 1543-1546
Insertion of helium and hydrogen
into an opened fullerene
Ever since it was discovered in the early nineties, buckminsterfullerene has kept many scientists busy. Among the features that make this soccer-ball shaped cage made of 60 carbon atoms so interesting is the large cavity at its center. It really just calls out for someone to put atoms or smaller molecules into it. This could lead to the formation of materials with interesting new properties. Until now, however, synthetic procedures have not been satisfactory.
American chemists working with Yves Rubin, Martin Saunders and Ken Houk have taken a new approach to filling the hollow soccer ball; they are working as "molecular surgeons". Like in an operation, the fullerene is first carefully opened in one place - through a chemical reaction. The co-reactant then acts like a surgical clamp, holding the resulting hole open.
Small particles can then be introduced through this inviting opening. The researchers first tried to insert an atom of the noble gas helium. Even under mild conditions (3 atm, 100 °C), a helium atom can be smuggled into one of these open cages.
The insertion of a dumbbell-shaped hydrogen molecule proved to be a bit more difficult. The opened fullerene, a crystalline powder, had to be heated to about 400 °C under a hydrogen pressure of 100 atm. Nearly 30 % of the cage-shaped molecules decomposed under these conditions. Of those that remained intact, 5 % wound up with an "inhabitant". This may sound like a small number, but it is by far the best result yet obtained for the direct insertion of a gas into a fullerene. "It should be possible to further increase the number of inserted gas molecules under conditions of extreme pressure," Rubin is confident.
There are further plans to introduce larger molecules and metal ions into fullerene derivatives. To do this the researchers will need to increase the size of the opening accordingly. Also, the final step of the "surgical operation" has yet to be completed; the wound has to be "sewn up". Initial results look promising. Despite severe deformation, the fullerene cage seems to be able to return to its soccer-ball shape.
However, the open fullerene does not only point the way toward new materials, it can also be used as a trial system for examining the passage of small molecules or ions through narrow channels to learn more about certain key biological processes.