Soot containing Tb₂C₉₀ was synthesized in a modified Krätschmer-Huffman generator by vaporizing composite graphite rods (8 × 150 mm) filled a mixture of Tb₄O₇ (99.99%) and graphite powder (molar ratio of Tb: C = 1 : 15) under 400 mbar He atmosphere. The as-produced soot was collected and dispersed in 1, 2, 4-trichlorobenzene (TCB). After refluxing for 12 h, the resulting brown-yellow solution was distilled to remove TCB and immediately redissolved in toluene, and then subjected to HPLC for the isolation of Tb₂C₉₀ isomers. For endohedral fullerenes with two metal atoms, M₂@C_2n, there are two possible structures, i.e. dimetallofullerene, M₂@C_2n, and metal carbide fullerene, M₂(μ-C₂)@C_2n-2. The UV-Vis-NIR absorption spectra of endohedral fullerenes are largely dependent on the fullerene cages and their electronic structures,¹ since they are mostly due to the π−π^* transitions of the fullerenes cages. Because the UV-Vis-NIR absorption spectra of Tb₂C₉₀（I）and Tb₂C₉₀（II）show much similar absorption features to those of Sm₂@C₁(21)-C₉₀ and Sc₂C₂@C_s(hept)C₈₈,^2-3 respectively, Tb₂C₉₀（I）isomer is estimated to be of Tb₂@C₁(21)-C₉₀ structure, and Tb₂C₉₀（II）isomer of Tb₂C₂@C_s(hept)-C₈₈structure. Electrochemical characterization confirms that the redox properties of endohedral metallofullerenes are tremendously dependent on the structures of carbon cage.

References

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[2] Chen CH, Abella L, Cerón MR et al. J. Am. Chem. Soc. 2016, 138(39): 13030-13037

[3] Zhang Y, Ghiassi KB, Deng Q et al. Angew. Chem., Int. Ed. 2014, 54(2): 495-499