Preferential Encapsulation and Stability of La3N Cluster in 80 Atom Cages: Experimental Synthesis and Computational Investigation of La3N@C79N

We report the synthesis and electronic stabilization of La3N@C79N. Unsuccessful efforts to encapsulate bulky La3N clusters in small C80 cages have been attributed to large ionic radii. The preferred species for La3N clusters in all-carbon cages is La3N@C96. A surprising finding is the synthesis of La3N@C79N, a new metallofullerene present in higher abundance than La3N@C96. This reduction in cage size from 96 to 80 atoms reflects the significance and role of electronic effects. To understand the geometric and electronic properties of this first metallic nitride azafullerene (M3N@C79N, M = La), density functional theory (DFT) investigations were performed on a number of isomers. Results indicate a preferred N-substitution at the 665 junction site on the cage in lieu of a 666 substitution. The relative stabilities of different isomers can be well reproduced by using the minimum distance between the metal atom and the nitrogen atom of the cage (R N′M min). Long R N′M min values indicate distant contacts between six atoms that bear significantly large positive charges: the three metal atoms and the three carbon atoms bonded with the nitrogen atom in the cage, which are favored. These results suggest a dominant electronic effect on the stabilities of metalloazafullerenes. Interestingly, spin densities of the 665 substitution isomers of La3N@C79N are located predominantly in the metal cluster, while spin densities of the 666 substitution isomers are primarily on the cage.