Ythrene: From the Real Radical Fullerene Substructure to Hypothetical (yet?) Radical Molecules

Among higher fullerenes that obey the isolated pentagon rule (IPR), there is an appreciable share of fullerenes with open electron shells. For a long time, this rule was used as a criterion for fullerene stability. Notwithstanding the IPR, fullerene radicals are unstable as pristine fullerenes but may be stabilized as their derivatives. Mainly, the molecules of such fullerenes contain phenalenyl-radical substructures. Here, for the first time, we found and theoretically investigated a new radical substructure of fullerene molecules of IPR isomer 7 (C3v) of C82 that bears two unpaired electrons and of IPR isomer 822 (D3d) of C104 with two equivalent substructures (four unpaired electrons). The fullerenes were obtained, and their molecular structures reliably characterized experimentally as endohedral derivatives. According to our computations, two hypothetical polyaromatic radical molecules C34H18 and C34H12, which are the models of the fullerene substructure, have the same open-shell triplet ground states...