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

The structure of crystalline [60]fullerene with a lithium cation inside (Li(+)@C(60)) was determined by synchrotron radiation X-ray diffraction measurements to understand the electrostatic and thermal properties of the encapsulated Li(+) cation. Although the C(60) cages show severe orientation disorder in [Li(+)@C(60)](TFPB(−))·C(4)H(10)O and [Li(+)@C(60)](TFSI(−))·CH(2)Cl(2), the Li(+) cations are rather ordered at specific positions by electrostatic interactions with coordinated anions outside the C(60) cage. The Li(+)@C(60) molecules in [Li(+)@C(60)](ClO(4)(−)) 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(4)(−) tetrahedra and show no orientation ordering, unlike [Li(+)@C(60)](PF(6)(−)) and pristine C(60). Single-bonded (Li(+)@C(60)(−))(2) dimers in [Li(+)@C(60)(−)](NiOEP)⋅CH(2)Cl(2) are thermally stable even at 400 K and form Li(+)–C bonds which are shorter than Li(+)–C bonds in [Li(+)@C(60)](PF(6)(−)) and suppress the rotational motion of the Li(+) cations.