M@C2(10612)-C72 (M = Ce, Gd): synthesis and characterization of open-shell paramagnetic mono-metallofullerenes

Abstract

Paramagnetic metallofullerenes are critical as exceptionally promising spin materials, yet their characteristic open-shell electronic configurations make them challenging to stabilize and isolate. Herein, we report the successful synthesis and isolation of two paramagnetic mono-metallofullerenes, M@C₂(10612)-C₇₂ (M = Gd, Ce), which possess an open-shell electronic configuration but are stably isolable in their pristine form. The crystallographic analysis reveals that Ce@C₂(10612)-C₇₂ is isolable in its pristine form without exohedral stabilizing functionalization and bears a non-IPR carbon cage featuring a pair of adjacent pentagons. The spectroscopic characterization of M@C₂(10612)-C₇₂ support a three-electron transfer from the encapsulated metal, endowing the fullerene compounds with paramagnetic properties. This work updates our understanding of open-shell paramagnetic mono-metallofullerenes, demonstrating that paramagnetic small-caged mono-EMFs can also exist stably without external stabilizing groups and provide a new paradigm for the development of metallofullerene-based spin materials.