Nitrogen violation of the isolated pentagon rule

We examine a range of fullerene isomers with and without the presence of nitrogen using density-functional-based calculations. We show that nitrogen stabilizes those with neighboring pentagons, allowing sp(2) bonded carbon networks to overcome the conventional rule that paired pentagons are not allowed through energetic constraints. This implies a new family of azafullerenes containing nitrogen-stabilized pentagon pairs, many of which will be considerably smaller than C-60. We discuss the relevance for nitrogen-doped nanotube structures and the topological importance for nanotube distortion and closure.