Cage closed

Polycyclic aromatic compounds sitting on a platinum surface lose their hydrogen atoms at 750 K and are zipped up to form fullerene molecules

Credit: © 2008 NPG

Perhaps the best-known method for making fullerenes involves vapourizing a carbon source in an inert atmosphere to produce a soot from which predominantly C₆₀ and some larger cages can be isolated. Such brute-force approaches do not, however, offer any way in which the synthesis can be modified to target a wider variety of fullerenes or their derivatives. Using molecular precursors that contain the correct atoms for a given fullerene enables more control over the products, but only in very low yields.

Researchers in Spain have now shown that a much more efficient synthesis¹ occurs if the reaction is performed on a surface, rather than in the gas phase. The team, lead by Berta Gómez-Lor and José Martín-Gago from the Instituto de Ciencia de Materiales de Madrid, deposited aromatic molecules with the formula C₆₀H₃₀ on a platinum surface and heated the sample to 750 K. This resulted in the platinum-catalysed cyclodehydrogenation of the C₆₀H₃₀ precursors, which zip themselves up to form C₆₀ molecules. It is suggested that strong interactions with the platinum surface distort the precursor molecules into a geometry that promotes the cyclodehydrogenation reaction.

Scanning tunnelling microscope images of the metal surface before and after the reaction show that all of the adsorbed molecules are converted into fullerenes. Moreover, the ability to make particular fullerene targets is demonstrated by using a precursor compound with the formula C₅₇H₃₃N₃, which reacts on the surface to form triazafullerenes (C₅₇N₃).