89Y and 13C NMR Cluster and Carbon Cage Studies of an Yttrium Metallofullerene Family, Y3N@C2n (n = 40−43)
Wujun Fu, Liaosa Xu, Hugo Azurmendi, Jiechao Ge, Tim Fuhrer, Tianming Zuo, Jonathan Reid, Chunying Shu, Kim Harich and Harry C. Dorn*
The members of a new family of yttrium trimetallic nitride-templated (TNT) endohedral metallofullerenes (EMFs), Y3N@C2n (n = 40−43), have been synthesized and purified. On the basis of experimental and computational 13C NMR studies, we propose cage structures for Y3N@Ih-C80 (IPR allowed), Y3N@D5h-C80 (IPR allowed), Y3N@Cs-C82 (non-IPR), Y3N@Cs-C84 (non-IPR), and Y3N@D3-C86 (IPR allowed). A significant result is the limited number of isomers found for each carbon cage. For example, there are 24 isolated pentagon rule (IPR) and 51568 non-IPR structures possible for the C84 cage, but only one major isomer of Y3N@Cs-C84 was found. The current study confirms the unique role of the trimetallic nitride (M3N)6+ cluster template in the Krtschmer−Huffman electric-arc process for fullerene cage size and high symmetry isomer selectivity. This study reports the first 89Y NMR results for Y3N@Ih-C80, Y3N@Cs(51365)-C84, and Y3N@D3(19)-C86, which reveal a progression from isotropic to restricted (Y3N)6+ cluster motional processes. Even more surprising is the sensitivity of the 89Y NMR chemical shift parameter to subtle changes in the electronic environment at each yttrium nuclide in the (Y3N)6+ cluster (more than 200 ppm for these EMFs). This 89Y NMR study suggests that 89Y NMR will evolve as a powerful tool for cluster motional studies of EMFs.