Sc₂C₂@D_3h(14246)-C₇₄: A Missing Piece of the Clusterfullerene Puzzle

Clusterfullerenes with variable carbon cages have been extensively studied in recent years. However, despite all these efforts, C₇₄ cage-based clusterfullerene remains a missing piece of the puzzle. Herein, we show that single-crystal X-ray crystallographic analysis unambiguously assigns the previously reported dimetallofullerene Sc₂@C₇₆ to a novel carbide clusterfullerene, Sc₂C₂@D_3h(14246)-C₇₄, the first experimentally proven clusterfullerene with a C₇₄ cage. In addition, Sc₂C₂@D_3h(14246)-C₇₄ was charaterized by mass spectrometry, ultraviolet-visible-near-infrared absorption spectroscopy, ⁴⁵Sc nuclear magnetic resonance, and cyclic voltammetry. Comparative studies of the motion of the carbide cluster in Sc₂C₂@D_3h(14246)-C₇₄ and Sc₂C₂@C_2n (n = 40-44) revealed that a combination of factors, involving both the shape and size of the cage, is crucial in dictating the cluster motion. Moreover, structural studies of D_3h(14246)-C₇₄ revealed that it can be easily converted to C_s(10528)-C₇₂ and T_d(19151)-C₇₆ cages via C₂ desertion/insertion and Stone-Wales transformation. This suggests that D_3h(14246)-C₇₄ might play an important role in the growth pathway of clusterfullerenes.