A layered ionic crystal of polar Li@C60 superatoms

If the physical properties of C-60 fullerene molecules can be controlled in C-60 products already in use in various applications, the potential for industrial development will be significant. Encapsulation of a metal atom in the C-60 fullerene molecule is a promising way to control its physical properties. However, the isolation of C-60-based metallofullerenes has been difficult due to their insolubility. Here, we report the complete isolation and determination of the molecular and crystal structure of polar cationic Li@C-60 metallofullerene. The physical and chemical properties of Li@C-60 cation are compared with those of pristine C-60. It is found that the lithium cation is located at off-centre positions in the C-60-I-h cage interior and that the [Li+@C-60] salt has a unique two-dimensional structure. The present method of purification and crystallization of C-60-based metallofullerenes provides a new C-60 fullerene material that contains a metal atom.