The synthesis of endohedral metallofullerenes (EMFs) from a carbon soot sample of an arc discharge leads to a variety of EMFs that are obtained in different relative abundances. Several different guiding principles as the relative size of the metallic cluster respect to fullerene cage, the number of electrons that are formally transferred from the metallic cluster to the fullerene cage and electrostatic repulsion between charged five-carbon rings have been used to explain the choice of the EMF most stable cages.¹ However, no single factor was capable to predict the most stable isomer for all EMFs. Our group has proposed that maximum aromaticity is the driving force that determines the most suitable hosting carbon cage for a given metallic cluster.² The most stable anionic fullerene isomer is the one whose total aromaticity is maximized. Our results show that maximum aromaticity criterion (MARC) successfully predicts the most suitable C_2n cage isomer for the endohedral metallofullerenes with carbon cages from C₆₆ to C₁₀₄. Furthermore, we have used electronic-based aromaticity measures to show that relative abundances of Sc₃N-based EMFs correlate with the aromaticity measures. Our results show that, for the Sc₃N-based EMFs, the most abundant EMFs are the most aromatic. This result reinforces the idea that aromaticity plays a key role in determining the stability of EMFs.

1. Garcia-Borras, M.; Osuna, S.; Luis, J. M.; Swart, M.; Sola, M. Chem-ical Society Reviews 2014, 43, 5089.

2. M. GarciaBorràs, S. Osuna, M. Swart, J.M. Luis, and M. Solà, Angew. Chem. Int. Ed. 2013, 52, 9275.