Where Does the Metal Cation Stay in Gd@<i>C</i>_2<i>v</i>(9)-C₈₂? A Single-Crystal X-ray Diffraction Study

Metal positions in endohedral metallofullerenes (EMFs) are of special importance because their molecular symmetry and intrinsic properties are strongly influenced by the location and motion of the encapsulated metals. X-ray analyses of the cocrystals of Gd@C2v(9)-C82 with nickelII octaethylporphyrin [NiII(OEP)] reveal that the Gd3+ cation is off-center, being located under a hexagonal ring along the 2-fold axis of the C2v(9)-C82 cage. This result is in sharp contrast to that of a previous study, showing that Gd@C2v(9)-C82 has an anomalous endohedral structure, with the metal being positioned over a [6,6] bond, which is opposite to the hexagonal ring along the C2 axis (Phys. Rev. B 2004, 69, 113412). In agreement with theoretical calculations and related studies, it is conclusive that the single rare-earth metal in M@C2v(9)-C82 always tends to coordinate with the hexagonal ring along the 2-fold axis, instead of interacting with the [6,6] bond on the other end, regardless of the type of metal atom.