Steering Lu 3 N clusters in C 76-78 cages: cluster configuration dominated by cage transformation.

While the strong interaction between the internal unit and the fullerene cage inside metallofullerenes is widely acknowledged, how the cage transformation interacts with the cluster configuration remains elusive. For this purpose, we herein synthesized three metallofullerene molecules with an easy-to-compare cluster configuration and cage arrangement, namely Lu 3 N@ C s (17 490)-C 76 , Lu 3 N@ C 2 (22 010)-C 78 , and Lu 3 N@ D 3 h (5)-C 78 . The three lutetium-based nitride clusterfullerenes (NCFs) with small C 76-78 carbon cages were synthesized by a modified arc-discharge method and their structures were unambiguously confirmed by X-ray crystallography. Notably, the cage transformation from C s (17 490)-C 76 to C 2 (22 010)-C 78 via a simple C 2 -unit insertion leads to a remarkable configuration change of the encapsulated Lu 3 N cluster from an unusual asymmetric plane to a common symmetric one. This close correlation between the cluster configuration and cage transformation is further confirmed by the pyramidal Lu 3 N cluster in Lu 3 N@ D 3 h (5)-C 78 other than the symmetric planar Lu 3 N unit in Lu 3 N@ C 2 (22 010)-C 78 , as a result of an even larger difference in the cage arrangement. Astonishingly, such a cluster shrinkage, accompanied by an increase in the cage size from C s (17 490)-C 76 to D 3 h (5)-C 78 , is dramatically opposite to the cluster expansion with cage elongation found in La 2 C 2 - or Y 2 C 2 -based metallofullerenes.