A Bent Tb₂C₂ Cluster Encaged in a C_S (6)-C₈₂ Cage: Synthesis, Isolation and X-ray Crystallographic Study

Terbium (Tb)-based dimetallofullerene, Tb2C84, has been synthesized and isolated by multistep HPLC. According to the UV-vis-NIR spectroscopic characterization and comparison with the reported analogous M2C84 (M = Sc, Y) metallofullerenes, the molecular structure of Tb2C84 is proposed to be Tb2C2@Cs (6)-C82 featuring a metal carbide clusterfullerene (CCF) structure, which is unambiguously confirmed by X-ray crystallographic study. A detailed analysis of the crystal structure of a cocrystal of Tb2C2@Cs (6)-C82·NiII(OEP)·2C6H6 (NiII(OEP) = nickel (II) octaethylporphyrin) reveals that a bent Tb2C2 carbide cluster is encaged rigidly inside a Cs (6)-C82 cage. The C-C bond within the encaged Tb2C2 carbide cluster behaves as a typical C-C triple bond. The asymmetric unit in Tb2C2@Cs (6)-C82·NiII(OEP)·2C6H6 contains two fullerene sites, for which the encaged Tb2C2 carbide cluster however locates at nearly the same position with one Tb atom being beneath a hexagon and another Tb atom pointing to the conjunction of two adjacent hexagons.