Highly delocalized endohedral metal in Gd@C_2v(9)-C₈₂ metallofullerenes co-crystallized with α-S₈

A new Gd@C_2v(9)-C₈₂·2.5(S₈)·0.5(CS₂) co-crystal was prepared for the first time and characterized by single-crystal X-ray diffraction (XRD). The analysis clearly showed that, even though the C_2v(9)-C₈₂ cage is fully ordered, the endohedral Gd atoms are highly disordered. This result indicates the presence of highly delocalized endohedral Gd atoms, which has never been reported before. Density functional theory (DFT) calculations were used to rationalize the XRD results. The calculations reveal the presence of two local energy minima, a and b, with the latter existing as four conformers b1–b4. Whereas the energy difference between the two minima is calculated only ~ 10 kcal/mol, their interconversion is almost impossible due to a high energy barrier, of up to 35.98 kcal/mol. This suggests the existence of multiple low-energy positions for the endohedral Gd atom. In addition, a remarkable electron transfer from the C_2v(9)-C₈₂ cage to the S₈ moieties was demonstrated, which might result in a modified endohedral environment and further contribute to the occurrence of delocalized endohedral Gd atoms.