Isolation and Electrochemical Property of Ho2O@C-90 Isomers

Four oxide clusterfullerenes Ho2O@C-90 (I-IV) were prepared by a modified arc discharge method and isolated by a multistage high performance liquid chromatography procedure. Based on their vis-NIR spectra, the carbon cage symmetries in Ho2O@C-90 (I, III, IV) are confirmed to be C (2)(43)-C-90, C (2)(40)-C-90 and C (2)(41)-C-90, respectively. Electrochemical studies display that the first and second reduction potentials of Ho2O@C-90 isomers are close to those of Er2C2@C-90 ones, but much lower than those of Sm@C-90 ones. Moreover, it is found that the electrochemical band gaps of Ho2O@C-90 isomers are also very close to those of Er2C2@C-90 isomers. A detailed investigation on the redox potentials of C-90 based EMFs reveals that endohedral clusters/atoms have much greater effect than carbon cage symmetries on the electrochemical properties of EMFs.