Cyclocarbon coalescence: mechanisms for tailor-made fullerene formation.

The availability of macroscopic quantities of fullerenes has resulted in a vast number of physical and chemical studies of these new materials. However, the mechanisms that lead to the formation of these spherical carbon allotropes are not well understood. Mass spectral evidence has been obtained for the size-selective growth of fullerenes through the coalescence of cyclo[n] carbons, molecular carbon allotropes consisting of monocyclic rings with n carbon atoms. Whereas coalescence of cyclo[30]carbon (cyclo-C(30)) produces predominantly buckminsterfullerene (C(60)), the smaller rings cyclo-C(l8) and cyclo-C(24) preferentially produce fullerene C(70) through distinct intermediates. The present studies not only provide new insights into fullerene formation mechanisms but also raise the possibility of tailoring the size distributions of fullerenes by variation of the appropriate properties of the precursors.