Mapping the metal positions inside spherical C_(80) cages: Crystallographic and theoretical studies of Ce_2@D_(5h)-C _(80) and Ce_2@I_h-C_(80)

摘要

The dynamic positions of the dimetallic cluster inside the mid-sized spherical cages of C_(80)-C_(82) have been seldom studied, despite the high abundance of M_2@C_(2n) (2n=80, 82) species among various endohedral metallofullerenes. Herein, using crystallographic methods, we first unambiguously map the metal positions for both Ce _2@D_(5h)-C_(80) and Ce_2@I _h-C_(80), showing how the symmetry or geometrical change in cage structure can influence the motional behavior of the cluster. Inside the D_(5h) cage, the primary cerium sites have been identified along a cage belt of the contiguous hexagons, which suggests the significant influence of such a cage motif on endohedral cluster motion. Further analysis revealed a distorted D5h cage owing to the "punch-out" effect of cerium atoms. The consequence is the presence of two localized electrostatic potential minima inside the cage of (D_(5h)-C_(80)) ~(6-), thus reflecting the primary ionic cerium-cage interaction. In contrast, a different motional behavior of Ce_2 cluster was observed inside the I_h cage. With the major cerium sites, the molecule of Ce_2@I_h-C_(80) presented an approximate D _(2h) configuration. With the combined theoretical study, we propose that the additional unidentified influence of Ni~(II)(OEP) (OEP=octaethylporphyrin) might be also relevant for the location of cerium sites inside the I_h cage. Acting cagey: Dynamic metal positions inside spherical C80 cages can be visualized by using crystallographic methods. A comparison study between Ce_2@D_(5h)-C_(80) and Ce_2@I_h-C_(80) (see figure) shows us how changes in the cage structure can influence the motional behaviors of the Ce_2 cluster