Enhanced Dipole Moments in Trimetallic Nitride Template Endohedral Metallofullerenes with the Pentalene Motif

摘要

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 Y_3N@C_(2n) (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 Y_3N@C_2-C_(78), Y_3N@C_5-C_(82), and Y_3N@C_5-C_(84) are examples that pentalene groups lead to a significant induced dipole moment (～1D). A special case is the Y_3N@C_2-C_(78) that contains two pentalenes in a relatively small cage. The ~13C NMR spectrum for Y_3N@C_2-C_(78) 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 M_3N cluster is found for all reported TNT EMFs that contain one or two pentalene motifs.