Isolation and Electrochemical Property of Tb@C₈₂ Isomers

Abstract

Carbon soot containing terbium endohedral fullerenes was prepared by vaporizing a graphite rod filled with Tb 4 O 7 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@C 82. The successful isolation of Tb@C 82 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@C 82 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@C 82 isomers was recorded in a 0.1 mol/L ortho-dichlorobenzene (o-DCB) solution of tetrabutylammonium hexafluorophosphate (TBAPF 6) 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@C 82 (I) exhibits two pairs of reversible oxidative and five pairs of reversible reductive peaks, and Tb@C 82 (II) shows one reversible oxidative and six reversible reductive ones. It is found that the symmetry of C 82 cage has little effect on the reduction potentials but great effect on the oxidation potentials of Tb@C 82 isomers. Moreover, the first reduction potential of both Tb@C 82 isomers is relatively high, indicating that they are good electron accepting materials. Additionally, the corresponding redox potentials of Tb@C 82 (II) are relatively higher than those of Tb@C 82 (I), therefore it is concluded that Tb@C 82 (II) is of better electron accepting ability than Tb@C 82 (I). In comparison with those reported previously, three pairs of reversible reductive and one pair of reversible oxidative peaks were initially detected for Tb@C 82 (I), offering more information on the electrochemistry of metallofullerene.

The Various Packing Structures of Tb@C82 (I, II) Isomers in Their Cocrystals with Ni(OEP)

“…It was reported for TbCN@C 82 and TbCN@C 76 that TbNC clusters are flexible, and the geometry of the embedded TbNC clusters and the length of the Tb-N(C)/C-N bond can be greatly changed by changing the size of the isomer or carbon cage structure. However, the crystalline structures of Tb-containing mono-EMFs have not been reported yet, even though some of them have been isolated and characterized electrochemically and spectroscopically [ 33 , 34 ].…”

Isolation and Electrochemical Property of Ho2O@C90 Isomers

“…According to the systematic electrochemical studies on a series of samarium-encapsulated EMFs, 29 it is proposed that with the increase in the size of carbon cage, the effect of electron transfer from endohedral metal atom(s) to carbon cages gets weaker and weaker, while the effect of carbon cages' size and symmetry gets stronger and stronger on the electrochemical properties of EMFs. We previously reported the electrochemical properties of Tb@C 82 (I, II), Tb 2 C 90 (I, II) and Ho 2 C 92 (I, II), [30][31][32] and found that the symmetry of carbon cage has little effect on their reduction process, but has a greater impact on their oxidation process. Lu et al reported the electrochemical properties of Y 2 C 2 @C 1 (1660)-C 108 (the EMF with the largest carbon cage isolated so far), 33 and found that its first oxidation potential is much lower than those of a series of Sc 2 C 2 @C 2n (2n = 72-88), reflecting the effect of the size and symmetry of carbon cage on the electrochemical properties of EMFs.…”