Stabilization of Giant Fullerenes C(41)-C, D(85)-C, C(132)-C, C(157)-C, and C(175)-C by Encapsulation of a Large LaC Cluster: The Importance of Cluster-Cage Matching.

Successful isolation and unambiguous crystallographic assignment of a series of higher carbide cluster metallofullerenes present new insights into the molecular structures and cluster-cage interactions of endohedral metallofullerenes. These new species are identified as LaC@C(41)-C, LaC@D(85)-C, LaC@C(132)-C, LaC@C(157)-C, and LaC@C(175)-C. This is the first report for these new cage structures except for D(85)-C. Our experimental and theoretical results demonstrate that LaC are more inclined to exist stably in the carbide form LaC@C rather than as the dimetallofullerenes La@C, which are rationalized by considering a synergistic effect of inserting a C unit into the cage, which ensures strong metal-cage interactions by partially neutralizing the charges from the metal ions and by fulfilling the coordination requirement of the La ions as much as possible.