Formation of Curvature Subunit of Carbon in Combustion.

Curvature prevalently exists in the world of carbon materials (e.g., fullerenes, buckyl bowls, carbon nanotubes, and onions), but traditional C2-addition mechanisms fail to elucidate the mechanism responsible for the formation of carbon curvature starting from a pentagonal carbon ring in currently available chemical-physical processes such as combustion. Here, we show a complete series of nascent pentagon-incorporating C5-C18 that are online produced in the flame of acetylene-cyclopentadiene-oxygen and in situ captured by C60 or trapped as polycyclic aromatic hydrocarbons for clarifying the growth of the curved subunit of C20H10. A mechanism regarding C1-substitution and C2-addition has been proposed for understanding the formation of curvature in carbon materials, as exemplified by the typical curved molecule containing a single pentagon completely surrounded by five hexagons. The present mechanism, supported by the intermediates characterized by X-ray crystallography as well as NMR, has been experimentally validated for the rational synthesis of curved molecule in the commercially useful combustion process.

Capturing the Fused-Pentagon C74 by Stepwise Chlorination.

As a bridge to connect medium-sized fullerenes, fused-pentagon C74 is still missing heretofore. Of 14 246 possible isomers, the first fused-pentagon C74 with the Fowler-Manolopoulos code of 14 049 was stabilized as C74Cl10 in the chlorine-involving carbon arc. The structure of C74Cl10 was identified by X-ray crystallography. The stabilization of pristine fused-pentagon C74 by stepwise chlorination was clarified in both theoretical simulation with density functional theory calculations and experimental fragmentation with multistage mass spectrometry.

Synthesis of long-sought C66 with exohedral stabilization.

Previously reported fused-pentagon fullerenes stabilized by exohedral derivatization do not share the same cage with those stabilized by endohedral encapsulation. Herein we report the crystallographic identification of (#4348)C66Cl10, which has the same cage as that of previously reported Sc2@C66. According to the geometrical data of (#4348)C66Cl10, both strain relief (at the fused pentagons) and local aromaticity (on the remaining sp(2)-hybrided carbon framework) contribute to the exohedral stabilization of this long-sought 66 carbon atom cage.