Crystallographic and Theoretical Investigations of Er2 @C2 n (2 n=82, 84, 86): Indication of Distance-Dependent Metal-Metal Bonding Nature

Abstract

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 Er₂ @C_s (6)-C₈₂ , Er₂ @C_3v (8)-C₈₂ , Er₂ @C₁ (12)-C₈₄ , and Er₂ @C_2v (9)-C₈₆ , in which the structure of the C₁ (12)-C₈₄ 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 Er₂ @C_s (6)-C₈₂ , Er₂ @C_3v (8)-C₈₂ , and Er₂ @C_2v (9)-C₈₆ form a two-electron-two-center Er-Er bond. However, for Er₂ @C₁ (12)-C₈₄ , 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 Er₂ @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.

Keywords: cluster compounds; density functional calculations; endohedral metallofullerenes; metal-metal bonds; structure elucidation.