Endohedral metallofullerenes (EMFs) are a new class of hybrid molecules formed by encapsulation of metallic species inside fullerene cages. They show unique structures, novel properties, and potential applications in such fields as photovoltaics, biomedicine, and materials science.

Scientists from China, Japan, and the United States obtained single crystals of three soluble Yb@C₈₂ isomers, namely, Yb@C₂(5)-C₈₂, Yb@C_s(6)-C₈₂, and Yb@C_2v(9)-C₈₂, cocrystallized with Ni^II(octaethylporphyrin). These allowed accurate crystallographic elucidation of their molecular structures in terms of both cage symmetry and metal location.

The results from these crystallographic studies agree with the results of previous ¹³C NMR studies that determined only the cage isomers present for these three EMFs. Moreover, the team found that the Yb²⁺ ion tends to be localized in some specific areas within the cages, regardless of the cage symmetry. These locations correspond to electrostatic potential minima and give the most stable configurations of these Yb@C₈₂ isomers.

• Single-Crystal X‑ray Diffraction Study of Three Yb@C₈₂ Isomers Cocrystallized with Ni^II(octaethylporphyrin),
  Mitsuaki Suzuki, Zdenek Slanina, Naomi Mizorogi, Xing Lu, Shigeru Nagase, Marilyn M. Olmstead, Alan L. Balch, Takeshi Akasaka,
  J. Am. Chem. Soc. 2012.
  DOI: 10.1021/ja308706d