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

Abstract

Herein, we report the preparation, purification, and characterization of a mixed trimetallic nitride endohedral metallofullerene, CeSc(2)N@C(80). Single-crystal X-ray diffraction shows that CeSc(2)N@C(80) consists of a four-atom asymmetric top (CeSc(2)N) inside a C(80) (I(h)()) carbon cage. Unlike the situation in most endohedrals of the M(3)N@C(2)(n)() type, the nitride ion is not located at the center of the carbon cage but is offset by 0.36 A in order to accommodate the large Ce(III) ion. The cage carbon atoms near the endohedral Ce and Sc atoms exhibit significantly larger pyramidal angles than the other carbon atoms on the C(80) cage. Surprisingly, at ambient temperature, the (13)C NMR spectrum exhibits isotropic motional averaging yielding only two signals (3 to 1 intensity ratio) for the icosahedral C(80) cage carbons. At the same temperature, the (45)Sc NMR exhibits a relatively narrow, symmetric signal (2700 Hz) with a small temperature-dependent Curie shift. A rotation energy barrier (E(a) = 79 meV) was derived from the (45)Sc NMR line-width analysis. Finally, the XPS spectrum for CeSc(2)N@C(80) confirms a +3 oxidation state for cerium, Ce(3+)(4f(1)5d(0)). This oxidation state and the Curie shift are consistent with a weakly paramagnetic system with a single buried f electron spin.