Theoretical Prediction of Divalent Actinide Borozene Complexes

The aromatic boron cluster B82– (D7h) has similar π bonding to C6H6, which is named “borozene”. The B82– ligand has been observed to stabilize monovalent Ln(+I) in C7v-LnB8− (Ln = La, Pr, Tb, Tm, and Yb) borozene complexes. Low-valency actinide complexes have been reported more rarely, and B82– may be one of the potential ligands. Here, we report a theoretical study on a series of actinide metal-doping octa-boron clusters AnB8 (An = Pa, U, Np, and Pu). It was found that each species has both half-sandwich and chair-like structures. Except for PaB8, the half-sandwich structures of UB8, NpB8, and PuB8 are more energetically stable than the chair-like structures, and the half-sandwich clusters of AnB8 are found to be actinide(II) borozene complexes with the MII[B82−] type. For each of the half-sandwich clusters, the B82− ligand has σ and π double aromaticity. Various bonding analyses of AnB8 confirm the covalent interactions between the doped actinide metals and the octa-boron clusters, which further stabilize the complexes and determine the relative stability of AnB8. As expected, these complexes show high bond dissociation energies, especially PaB8 with stronger Pa-B covalent bonds. These results demonstrate that the B82− doubly aromatic ligand is able to stabilize divalent actinides.