Crystallographic and Theoretical Investigations of Er @C (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 @C (6)-C , Er @C (8)-C , Er @C (12)-C , and Er @C (9)-C , in which the structure of the C (12)-C 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 @C (6)-C , Er @C (8)-C , and Er @C (9)-C form a two-electron-two-center Er-Er bond. However, for Er @C (12)-C , 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 @C are good electron donors instead of electron acceptors. Hence, this finding initiates a connection between metal-metal bonding chemistry and fullerene chemistry.