A diuranium carbide cluster stabilized inside a C-80 fullerene cage

Unsupported non-bridged uranium-carbon double bonds have long been sought after in actinide chemistry as fundamental synthetic targets in the study of actinide-ligand multiple bonding. Here we report that, utilizing I-h(7)-C-80 fullerenes as nanocontainers, a diuranium carbide cluster, U=C=U, has been encapsulated and stabilized in the form of UCU@I-h(7)-C-80 . This endohedral fullerene was prepared utilizing the Kratschmer-Huffman arc discharge method, and was then co-crystallized with nickel(II) octaethylporphyrin (Ni-II-OEP) to produce UCU@I-h(7)-C-80 center dot[ Ni-II-OEP] as single crystals. X-ray diffraction analysis reveals a cage-stabilized, carbide-bridged, bent UCU cluster with unexpectedly short uranium-carbon distances (2.03 angstrom) indicative of covalent U=C double-bond character. The quantum-chemical results suggest that both U atoms in the UCU unit have formal oxidation state of +5. The structural features of UCU@I-h(7)-C-80 and the covalent nature of the U(f(1))=C double bonds were further affirmed through various spectroscopic and theoretical analyses.