The structure of crystalline fullerene with a lithium cation inside (Li+@C60) was determined by synchrotron radiation X-ray diffraction measurements to understand the electrostatic and thermal properties of the encapsulated Li+ cation. Although the C60 cages show severe orientation disorder in [Li+@C60](TFPB-)·C4H10O and [Li+@C60](TFSI-)·CH2Cl2, the Li+ cations are rather ordered at specific positions by electrostatic interactions with coordinated anions outside the C60 cage. The Li+@C60 molecules in [Li+@C60](ClO4 -) with a rock-salt-type cubic structure are fully disordered with almost uniform spherical shell charge densities even at 100K by octahedral coordination of ClO4 - tetrahedra and show no orientation ordering, unlike [Li+@C60](PF6-) and pristine C60. Single-bonded (Li+@C60 -)2 dimers in [Li+@C60 -](NiOEP)·CH2Cl2 are thermally stable even at 400K and form Li+-C bonds which are shorter than Li+-C bonds in [Li+@C60](PF6-) and suppress the rotational motion of the Li+ cations.
- Endohedral metallofullerene
- Synchrotron radiation
- X-ray crystal structure analysis
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