Monometallic Endohedral Azafullerene

Azafullerenes derived from nitrogen substitution of carbon cage atoms render direct modifications of the cage skeleton, electronic, and physicochemical properties of fullerene. Gas-phase ionized monometallic endohedral azafullerene (MEAF) [La@C₈₁N]⁺ formed via fragmentation of a La@C₈₂ monoadduct was detected in 1999, but the pristine MEAF has never been synthesized. Here, we report the synthesis, isolation, and characterization of the first pristine MEAF La@C₈₁N, tackling the two-decade challenge. Single-crystal X-ray diffraction study reveals that La@C₈₁N has an 82-atom cage with a pseudo C_3v(8) symmetry. According to DFT computations, the nitrogen substitution site within the C₈₂ cage is proposed to locate at a hexagon/hexagon/pentagon junction far away from the encapsulated La atom. La@C₈₁N exists in stable monomer form with a closed-shell electronic state, which is drastically different from the open-shell electronic state of the original La@C₈₂. Our breakthrough in synthesizing a new type of azafullerene offers a new insight into the skeletal modification of fullerenes.