Crystallographic and Theoretical Investigations of Er 2 @C 2 n (2 n= 82, 84, 86): Indication of Distance‐Dependent Metal–Metal Bonding Nature

Successful isolation and characterization of a series of Er‐based dimetallofullerenes present valuable insights into the realm of metal–metal bonding. These species are crystallographically identified as Er 2 @ C s (6)‐C 82 , Er 2 @ C 3 v (8)‐C 82 , Er 2 @ C 1 (12)‐C 84 , and Er 2 @ C 2 v (9)‐C 86 , in which the structure of the C 1 (12)‐C 84 cage is unambiguously characterized for the first time by single‐crystal X‐ray diffraction. Interestingly, natural bond orbital analysis demonstrates that the two Er atoms in Er 2 @ C s (6)‐C 82 , Er 2 @ C 3 v (8)‐C 82 , and Er 2 @ C 2 v (9)‐C 86 form a two‐electron‐two‐center Er−Er bond. However, for Er 2 @ C 1 (12)‐C 84 , with the longest Er⋅⋅⋅Er distance, a one‐electron‐two‐center Er−Er bond may exist. Thus, the difference in the Er⋅⋅⋅Er separation indicates distinct metal bonding natures, suggesting a distance‐dependent bonding behavior for the internal dimetallic cluster. Additionally, electrochemical studies suggest that Er 2 @C 82–86 are good electron donors instead of electron acceptors. Hence, this finding initiates a connection between metal–metal bonding chemistry and fullerene chemistry.