Electrochemical reduction of cationic Li@C to neutral Li@C˙: isolation and characterisation of endohedral [60]fulleride.

Lithium-encapsulated [60]fullerene Li@C, namely, lithium-ion-encapsulated [60]fullerene radical anion Li@C˙, was synthesised by electrochemical reduction of lithium-ion-encapsulated [60]fullerene trifluoromethanesulfonylimide salt [Li@C](TFSI). The product was fully characterised by UV-vis-NIR absorption and ESR spectroscopy as well as single-crystal X-ray analysis for the co-crystal with nickel octaethylporphyrin. In solution Li@C exists as a monomer form dominantly, while in the crystal state it forms a dimer (Li@C-Li@C) through coupling of the C radical anion cage. These structural features were supported by DFT calculations at the M06-2X/6-31G(d) level of theory.