Enhanced dipole moments in trimetallic nitride template endohedral metallofullerenes with the pentalene motif.

Although not found to date in empty-cage fullerenes, the fused pentagon motifs (pentalenes) are allowed in endohedral metallofullerenes (EMFs). We have found that members of the trimetallic nitride template (TNT) EMF Y3N@C2n (n = 39–44) family that contain pentalene motifs exhibit significant dipole moments. This finding is predicted to be significant for other EMFs with a metal atom orientated toward the pentalene motif. Chromatographic retention data and computational results for Y3N@C2-C78, Y3N@Cs-C82, and Y3N@Cs-C84 are examples that pentalene groups lead to a significant induced dipole moment (∼1D). A special case is the Y3N@C2-C78 that contains two pentalenes in a relatively small cage. The 13C NMR spectrum for Y3N@C2-C78 exhibits strongly deshielded signals for the fullerene cage (155–170 ppm) supporting the presence of the pentalene motif. In addition, a lengthening of the covalent M–N bond in the internal M3N cluster is found for all reported TNT EMFs that contain one or two pentalene motifs.