Electrochemical reduction of cationic Li+@C60to neutral Li+@C60˙−: isolation and characterisation of endohedral [60]fulleride

Lithium-encapsulated [60]fullerene Li@C60, namely, lithium-ion-encapsulated [60]fullerene radical anion Li+@C60˙−, was synthesised by electrochemical reduction of lithium-ion-encapsulated [60]fullerene trifluoromethanesulfonylimide salt [Li+@C60](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@C60 exists as a monomer form dominantly, while in the crystal state it forms a dimer (Li@C60–Li@C60) through coupling of the C60 radical anion cage. These structural features were supported by DFT calculations at the M06-2X/6-31G(d) level of theory