Lithium-encapsulated fullerene Li@C60, namely, lithium-ion-encapsulated fullerene radical anion Li+@C60-, was synthesised by electrochemical reduction of lithium-ion-encapsulated 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.
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