Fig. 1. Selected examples for carbon allotropes (top row): diamond, graphite, γ-graphyne,4 carbon nanotube and cyclo[18]carbon.6 Selected examples for fullerenes Cn.12,13 Grey box: the most abundant endohedral metallofullerene Sc3N⊂Ih-C80 and heterofullerene (C59N)2 as examples for relevant compounds beyond carbon allotropes.10,14.
