关键词: 内嵌金属富勒烯, 铽, 异构体, 电化学, 氧化-还原电位

Carbon soot containing terbium endohedral fullerenes was prepared by vaporizing a graphite rod filled with Tb₄O₇ and graphite powder in an electric arc-discharge chamber. After reflux extraction with 1,2,4-trichlorobenzene and rotary evaporation of solvent, the residue was ultrasonically dissolved in toluene. The obtained solution was filtered with a 0.2 μm PTFE film, and then subjected to a three-stage high-performance liquid chromatographic (HPLC) isolation process to achieve two individual isomers of Tb@C₈₂. The successful isolation of Tb@C₈₂ isomers was confirmed by matrix-assisted laser desorption time-of-flight mass spectrometry and analytical HPLC. According to their UV-Vis-NIR absorption spectra, the carbon cages of the isolated Tb@C₈₂ isomers are estimated to be of C_2v and C_s symmetry, respectively, and Tb atom is encapsulated in carbon cage at a valence state of +3. The cyclic voltammetry (CV) of the two Tb@C₈₂ isomers was recorded in a 0.1 mol/L ortho-dichlorobenzene (o-DCB) solution of tetrabutylammonium hexafluorophosphate (TBAPF₆) by referring the ferrocene/ferrocenium couple (Fc/Fc⁺). The working electrode and the counter electrode were platinum wires, and the reference one was a Ag/AgCl electrode. Tb@C₈₂ (I) exhibits two pairs of reversible oxidative and five pairs of reversible reductive peaks, and Tb@C₈₂ (II) shows one reversible oxidative and six reversible reductive ones. It is found that the symmetry of C₈₂ cage has little effect on the reduction potentials but great effect on the oxidation potentials of Tb@C₈₂ isomers. Moreover, the first reduction potential of both Tb@C₈₂ isomers is relatively high, indicating that they are good electron accepting materials. Additionally, the corresponding redox potentials of Tb@C₈₂ (II) are relatively higher than those of Tb@C₈₂ (I), therefore it is concluded that Tb@C₈₂ (II) is of better electron accepting ability than Tb@C₈₂ (I). In comparison with those reported previously, three pairs of reversible reductive and one pair of reversible oxidative peaks were initially detected for Tb@C₈₂ (I), offering more information on the electrochemistry of metallofullerene.

Key words: metallofullerene, terbium, isomer, electrochemistry, redox potential