A charged diatomic triple-bonded U equivalent to N species trapped in C-82 fullerene cages

Diatomic actinide molecules are ideal models for studying rare multiple-bond motifs. Here, the authors report host-guest structures of metastable charged U equivalent to N diatoms confined in fullerene cages and stabilized by coordinative electron transfer. Actinide diatomic molecules are ideal models to study elusive actinide multiple bonds, but most of these diatomic molecules have so far only been studied in solid inert gas matrices. Herein, we report a charged U equivalent to N diatomic species captured in fullerene cages and stabilized by the U-fullerene coordination interaction. Two diatomic clusterfullerenes, viz. UN@C-s(6)-C-82 and UN@C-2(5)-C-82, were successfully synthesized and characterized. Crystallographic analysis reveals U-N bond lengths of 1.760(7) and 1.760(20) angstrom in UN@C-s(6)-C-82 and UN@C-2(5)-C-82. Moreover, U equivalent to N was found to be immobilized and coordinated to the fullerene cages at 100 K but it rotates inside the cage at 273 K. Quantum-chemical calculations show a (UN)(2+)@(C-82)(2-) electronic structure with formal +5 oxidation state (f(1)) of U and unambiguously demonstrate the presence of a U equivalent to N bond in the clusterfullerenes. This study constitutes an approach to stabilize fundamentally important actinide multiply bonded species.