Ultrastable actinide endohedral borospherenes

Abstract

Since the discovery of the first all-boron fullerenes B₄₀^−/0, metal-doped borospherenes have received extensive attention. So far, in spite of theoretical efforts on metalloborospherenes, the feasibility of actinide analogues remains minimally explored. Here we report a series of actinide borospherenes AnB_n (An = U, Th; n = 36, 38, and 40) using DFT-PBE0 calculations. All the AnB_n complexes are found to possess endohedral structures (An@B_n) as the global minima. In particular, U@B₃₆ (C_2h, ³A_g) and Th@B₃₈ (D_2h, ¹A_g) exhibit nearly ideal endohedral borospherene structures. The C_2h U@B₃₆ and D_2h Th@B₃₈ complexes are predicted to be highly robust both thermodynamically and dynamically. In addition to the actinide size match to the cage, the covalent character of the metal-cage bonding in U@B₃₆ and Th@B₃₈ affords further stabilization. Bonding analysis indicates that U@B₃₆ and Th@B₃₈ can be qualified as 32-electron systems, and Th@B₃₈ exhibits 3D aromaticity with σ plus π double delocalization bonding. The results demonstrate that doping with appropriate actinide atoms is promising to stabilize diverse borospherenes, and may provide routes for borospherene modification and functionalization.