Synthesis, isolation, characterization, and theoretical studies of Sc ₃NC@C₇₈- C₂

Following the first isolation of Sc₃NC@C₈₀, a second member of this family of endohedral metallofullerenes, Sc₃NC@C ₇₈, was prepared by an arc-discharging method. Experimental and theoretical studies demonstrated that the Sc₃NC@C₇₈ has a C₇₈-C₂ cage with two pairs of adjacent pentagons, which is different from the IPR-satisfying Sc₃N@C₇₈-D _3h. It was revealed that the size of C₇₈-D_3h is appropriate for the Sc₃N cluster, but not large enough for encaging the large planar species Sc₃NC. Theoretical calculations were preformed on Sc₃NC@C₇₈-C₂ and Sc ₃NC@C₇₈-D_3h. The results show that Sc ₃NC would bear a strong depression inside the C₇₈-D _3h fullerene cage due to the limited internal space of C ₇₈-D_3h; on the contrary, C₇₈-C₂ has two pairs of adjacent pentagons that induce a large curvature in these sites to form an oblate ellipsoid structure. Thus, it is more favorable to encapsulate the planar species Sc₃NC. Ab initio calculations were also performed to further disclose the electronic and electrochemical properties of Sc ₃NC@C₇₈-C₂. It was revealed that the molecule has an electronic structure of (Sc³⁺)₃(NC) ^3-@C₇₈^6-, in which the inner species NC has an unprecedented (NC)^3- trianion charging status similar to that in the recently reported Sc₃NC@C₈₀-I_h.