Toward Synthesis and Characterization of Unconventional C66 and C68 Fullerenes inside Carbon Nanotubes

We present compelling evidence pointing to the possible synthesis of unconventional C66 and C68 fullerenes in the interior of single-walled carbon nanotubes. The production proceeds from C60-toluene/benzene clathrates encapsulated inside the nanotubes using heat-driven nanotesttube chemistry. All isomers violate the so-called isolated pentagon rule and are stabilized solely by the proximity of the wall of the host nanotube. We present detailed characterization of the unconventional fullerenes using Raman spectroscopy, 13C isotope labeling of the benzene molecules, transmission electron microscopy, X-ray diffractometry, and first-principles calculations. Multiple isomers of both C66 and C68 are identified in the sample. We argue that our method opens the way to high-yield synthesis of unconventional fullerenes.