Ultrastable actinide endohedral borospherenes

Since the discovery of the first all-boron fullerenes B-40(-/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@B-36 (C-2h, (3)A(g)) and Th@B-38 (D-2h, (1)A(g)) exhibit nearly ideal endohedral borospherene structures. The C-2h U@B-36 and D-2h Th@B-38 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@B-36 and Th@B-38 affords further stabilization. Bonding analysis indicates that U@B-36 and Th@B-38 can be qualified as 32-electron systems, and Th@B-38 exhibits 3D aromaticity with sigma plus 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.