UN@C82: A U≡N Triple Bond Captured inside Fullerene Cages

Abstract Actinide diatomic molecules are ideal models to study elusive actinide multiple bonds, but they have only been studies in solid inert gas matrices to date. Here we report the unprecedented U ≡ N diatomic species captured in two different fullerene cages. UN@Cs(6)-C82 and UN@C2(5)-C82, the first diatomic clusterfullerenes, were successfully synthesized and fully characterized. X-ray single crystal diffraction reveals very short U-N bond lengths of 1.760 Å in both UN@Cs(6)-C82 and UN@C2(5)-C82. Moreover, U ≡ N was found to be immobilized and coordinated to the fullerene cages at 100 K but it spins inside the cage at 273 K. Quantum-chemical calculations show a (UN)2+@(C82)2− electronic structure with formal + 5 oxidation state (f1) of U and demonstrate the presence of a rare U ≡ N bond in the cluster fullerenes This study opens a new direction for endohedral fullerenes and constitutes a new approach to stabilize elusive yet fundamentally important actinide multiply bonded species.