Entrapped planar trimetallic carbide in a fullerene cage: Synthesis, isolation, and spectroscopic studies of Lu₃C₂@C ₈₈

We report the preparation, isolation, and spectroscopic characterizations of a novel endofullerene Lu₃C₂@C₈₈, where a planar trimetallic carbide cluster Lu₃C₂ is encapsulated by D₂-symmetric C₈₈ cage. Meanwhile, the trimetallic nitride endofullerene Lu₃N@C₈₈ was also isolated and characterized for comparison. The results revealed that both metal carbide Lu₃C₂ and metal nitride Lu₃N share the same D₂-symmetric C₈₈ cage. Theoretical studies revealed that the internal moieties supply the C₈₈ cage with six electrons in both Lu₃N@C₈₈ and Lu₃C₂@C₈₈ cases; however, Lu₃N@C₈₈ has a closed-shell electronic structure and Lu₃C₂@C₈₈ owns an unpaired electron localized on the internal [Lu₃C₂]⁶⁺ moiety. The different molecular electronic structures of Lu₃C ₂@C₈₈ and Lu₃N@C₈₈ lead to distinct differences on both the UV-vis absorption spectral features and their electrochemical redox properties.