Double Negatively Curved C70 Growth through a Heptagon‐Involving Pathway.

All previously reported C70 isomers have positive curvature and contain 12 pentagons in addition to hexagons. Herein, we report a new C70 species with two negatively curved heptagon moieties and 14 pentagons. This unconventional heptafullerene[70] containing two symmetric heptagons, referred to as dihept‐C70, grows in the carbon arc by a theoretically supported pathway in which the carbon cluster of a previously reported C66 species undergoes successive C2 insertion via a known heptafullerene[68] intermediate with low energy barriers. As identified by X‐ray crystallography, the occurrence of heptagons facilitates a reduction in the angle of the π‐orbital axis vector in the fused pentagons to stabilize dihept‐C70. Chlorination at the intersection of a heptagon and two adjacent pentagons can greatly enlarge the HOMO–LUMO gap, which makes dihept‐C70Cl6 isolable by chromatography. The synthesis of dihept‐C70Cl6 offers precious clues with respect to the fullerene formation mechanism in the carbon‐clustering process. [ABSTRACT FROM AUTHOR]