Theoretical Study on the Ground State Structure of Uranofullerene U@C<sub>82</sub>

Despite its experimental characterization, the detailed geometry and electronic structure of actinide metallofullerene U@C<sub>82</sub> have been rarely studied. We predict that <sup>#5</sup>C<sub>82</sub> and <sup>#8</sup>C<sub>82</sub> are the best cages for the encapsulation of monovalent and tetravalent U (i.e., U<sup>+</sup> and U<sup>4+</sup>), respectively; while <sup>#9</sup>C<sub>82</sub> is the best cage for divalent, trivalent, pentavalent, and hexavalent U cations (i.e., U<sup>2+</sup>, U<sup>3+</sup>, U<sup>5+</sup>, and U<sup>6+</sup>). U@<sup>#9</sup>C<sub>82</sub> is the thermodynamically most stable one among all the isomers and thus corresponds to the most experimentally isolable isomer of U@C<sub>82</sub>. The calculated spin density explicitly suggests that the endohedral metallofullerene U@<sup>#9</sup>C<sub>82</sub> is a trivalent ion-pair with an electronic configuration of U<sup>3+</sup>@C<sub>82</sub><sup>3–</sup>. The proposed geometry and electronic structure of U<sup>3+</sup>@<sup>#9</sup>C<sub>82</sub><sup>3–</sup> are in good agreement with the experimental observation.