An Expanded Family of Dysprosium-Scandium Mixed-Metal Nitride Clusterfullerenes

Metallic nitride clusterfullerene (NCF) is the most rapidly-growing branch of endohedral fullerenes because of its extraordinarily high yield and peculiar electronic structure with six-electron transfer from the encapsulated trimetallic nitride cluster to the outer carbon cage. A large family of dysprosium-scandium (Dy-Sc) mixed-metal nitride clusterfullerenes (MMNCFs), Dy_xSc_3-xN@C_2n (x=1, 2, 2n=68, 70, 76 - 86) have been successfully synthesized and isolated, among which the C₇₀ and C₈₂-based MMNCFs represent two new cages that have never been isolated for MMNCFs. Synthesis of Dy_xSc_3-xN@C_2n was accomplished by the “selective organic solid” route using guanidinium thiocyanate as the nitrogen source, and their isolation was fulfilled by recycling HPLC. UV-vis-NIR spectroscopic study indicates that almost all Dy_xSc_3-xN@C_2n MMNCFs are kinetically stable fullerenes with optical band-gaps beyond 1 eV. This feature is distinctly different to their counterparts Dy₃N@C_2n (78≤2n≤88), for which those with relatively large cages such as C₈₄ and C₈₆ have optical band-gaps below 1 eV. FTIR spectroscopic study in combination with DFT calculation enables successful assignments of the cage isomeric structures of all Dy_xSc_3-xN@C_2n (x=1, 2, 2n=68, 70, 76 - 86) MMNCFs. The carbon cage size distribution of Dy_xSc_3-xN@C_2n (2n=68, 70, 76 - 86) is compared to the reported Dy₃N@C_2n (78≤2n≤88) homogeneous NCF and Gd_xSc_3-xN@C_2n (78≤2n≤88) MMNCF families, revealing that the medium-sized Dy metal plays a crucial role on the expanded size distribution of MMNCFs. As a result, Dy_xSc_3-xN@C_2n MMNCFs represent the largest MMNCF family reported to date.