Crystallographic Characterization of U@C2n (2n=82-86): Insights about Metal-Cage Interactions for Mono-metallofullerenes

Endohedral mono-metallofullerenes are the prototypes to understand the fundamental nature and the unique interactions between the encapsulated metals and the fullerene cages. Herein, we report the crystallographic characterizations of four new U-based mono-metallofullerenes, namely, U@C-s(6)-C-82, U@C-2(8)-C-84, U@C-s(15)-C-84, and U@C-1(12)-C-86, among which the chiral cages C-2(8)-C-84 and C-1(12)-C-86 have never been previously reported for either endohedral or empty fullerenes. Symmetrical patterns, such as indacene, sumanene, and phenalene, and charge transfer are found to determine the metal positions inside the fullerene cages. In addition, a new finding concerning the metal positions inside the cages reveals that the encapsulated metal ions are always located on symmetry planes of the fullerene cages, as long as the fullerene cages possess mirror planes. DFT calculations show that the metal-fullerene motif interaction determines the stability of the metal position. In fullerenes containing symmetry planes, the metal prefers to occupy a symmetrical arrangement with respect to the interacting motifs, which share one of their symmetry planes with the fullerene. In all computationally analyzed fullerenes containing at least one symmetry plane, the actinide was found to be located on the mirror plane. This finding provides new insights into the nature of metal-cage interactions and gives new guidelines for structural determinations using crystallographic and theoretical methods.

Automated summary

The study presents crystallographic characterizations of four new U-based mono-metallofullerenes, highlighting the role of symmetrical patterns and charge transfer in determining the metal positions inside the fullerene cages. It also reveals that in fullerenes containing symmetry planes, the actinide metal ions tend to be located on the mirror plane, providing new insights into metal-cage interactions and guidelines for structural determinations.