Electrochemical reduction of cationic Li(+)@C(60) to neutral Li(+)@C(60)˙(–): isolation and characterisation of endohedral [60]fulleride

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