Structure of [60]fullerene with a mobile lithium cation inside.

The structure of crystalline [60]fullerene with a lithium cation inside (Li@C) was determined by synchrotron radiation X-ray diffraction measurements to understand the electrostatic and thermal properties of the encapsulated Li cation. Although the C cages show severe orientation disorder in [Li@C](TFPB)·CHO and [Li@C](TFSI)·CHCl, the Li cations are rather ordered at specific positions by electrostatic interactions with coordinated anions outside the C cage. The Li@C molecules in [Li@C](ClO) with a rock-salt-type cubic structure are fully disordered with almost uniform spherical shell charge densities even at 100 K by octahedral coordination of ClO tetrahedra and show no orientation ordering, unlike [Li@C](PF) and pristine C. Single-bonded (Li@C) dimers in [Li@C](NiOEP)⋅CHCl are thermally stable even at 400 K and form Li-C bonds which are shorter than Li-C bonds in [Li@C](PF) and suppress the rotational motion of the Li cations.