Radical character of non-IPR isomer 17418 (C₁) of fullerene C₇₆

Abstract Using a theoretical approach supported by DFT calculations, the features of molecular structure of isomer 17418 (C1) of fullerene C76 with the distribution of single, double and delocalized π-bonds has been determined for the first time. It is shown the radical nature together with the well-known overstrain due to pentalene fragment are the reasons for the instability of this fullerene as empty molecule. The synthesis of endohedral metallofulerenes is accompanied by the formation of an ion pair: the fullerene anion and a metal cation inside the molecule. It`s leading to the closure of the electron shell of the fullerene molecule and the removal of excess local strains. The previously experimentally determined cations sites inside the fullerene, which stabilize the molecule as a whole, are close to the disclosed radical clusters.