Fullerenes are all-carbon molecules. Exchanging one or more carbon atoms with another element gives heterofullerenes. This can be useful to tune the properties of fullerenes for specific applications. In azafullerenes, for example, carbon atoms have been substituted by nitrogen. Fullerenes can also be modified by encapsulating, e.g., metal atoms inside the cage to give endohedral fullerenes.

Alexey A. Popov, Leibniz Institute for Solid State and Materials Research, Dresden, Germany, Shangfeng Yang, University of Science and Technology of China, Hefei, and colleagues have combined these two types of modification and synthesized the first pristine monometallic endohedral azafullerene, La@C₈₁N. The team synthesized this species from a mixture of La₂O₃, TiO₂, and graphite using an arc-discharge method.

The product was isolated using high-performance liquid chromatography (HPLC). Its structure was investigated using single-crystal X-ray diffraction, employing a co-crystal with a decapyrrylcorannulene host. The results confirmed the presence of an 82-atom cage with an encapsulated La atom. The team found that La@C₈₁N exists in stable monomer form with a closed-shell electronic state, in contrast to the unstable, open-shell parent endofullerene La@C₈₂. The work could be useful for the development of new heterofullerenes with the aim of tailoring their electronic states.

• Monometallic Endohedral Azafullerene,
  Wenhao Xiang, Xiaole Jiang, Yang-Rong Yao, Jinpeng Xin, Huaimin Jin, Runnan Guan, Qianyan Zhang, Muqing Chen, Su-Yuan Xie, Alexey A. Popov, Shangfeng Yang,
  J. Am. Chem. Soc. 2022.
  https://doi.org/10.1021/jacs.2c08679