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

Abstract

Lithium-encapsulated [60] fullerene Li@C-60, namely, lithium-ion-encapsulated [60]fullerene radical anion Li+@C-60(center dot-), 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.