Preparation and Structure of CeSc₂N@C₈₀: An Icosahedral Carbon Cage Enclosing an Acentric CeSc₂N Unit with Buried f Electron Spin

Herein, we report the preparation, purification, and characterization of a mixed trimetallic nitride endohedral metallofullerene, CeSc2N@C80. Single-crystal X-ray diffraction shows that CeSc2N@C80 consists of a four-atom asymmetric top (CeSc2N) inside a C80 (Ih) carbon cage. Unlike the situation in most endohedrals of the M3N@C2n type, the nitride ion is not located at the center of the carbon cage but is offset by 0.36 Å in order to accommodate the large CeIII ion. The cage carbon atoms near the endohedral Ce and Sc atoms exhibit significantly larger pyramidal angles than the other carbon atoms on the C80 cage. Surprisingly, at ambient temperature, the 13C NMR spectrum exhibits isotropic motional averaging yielding only two signals (3 to 1 intensity ratio) for the icosahedral C80 cage carbons. At the same temperature, the 45Sc NMR exhibits a relatively narrow, symmetric signal (2700 Hz) with a small temperature-dependent Curie shift. A rotation energy barrier (Ea = 79 meV) was derived from the 45Sc NMR line-width analysis. Finally, the XPS spectrum for CeSc2N@C80 confirms a +3 oxidation state for cerium, Ce3+(4f15d0).This oxidation state and the Curie shift are consistent with a weakly paramagnetic system with a single buried f electron spin.