Theoretical prediction of chiral actinide endohedral borospherenes

Abstract

Recently, the observation of the first axially chiral borospherenes (B₃₉⁻) enriched the members of the boron cluster family, and opened the door to axially chiral boron cages. Herein, we theoretically predicted a series of chiral borospherenes by actinide metal (An) encapsulation, which are new chiral members of the borospherene family. Theoretical calculations demonstrate that the C₂ neutral and charged Ac– and Th–B₃₉ boron clusters (Ac@B₃₉, [Ac@B₃₉]²⁺, and Th@B₃₉, [Th@B₃₉]³⁺) are the most stable structures, and each borospherene possesses degenerate enantiomers, in accordance with the chiral borospherenes B₃₉⁻. In contrast, the global minimum structures of Cf embedded borospherenes have no symmetry (C₁). All the chiral actinoborospherenes [An@B₃₉]ⁿ⁺ (An = Ac, n = 0, 2; An = Th, n = 0, 3) possess high formation energies, especially C₂ [Th@B₃₉]³⁺. Bonding analysis shows that each complex of [Ac@B₃₉]ⁿ⁺ and [Th@B₃₉]ⁿ⁺ has the characteristic of σ + π double delocalization, and the Th–B bonds possess relatively higher covalency than the Ac–B bonds, resulting in the higher formation energy of C₂ [Th@B₃₉]³⁺. Therefore, the covalent character of An–B bonding may be essential for the formation of these chiral actinoborospherenes. This work extends the chiral borospherenes to actinide metal-doped chiral borospherenes, and sheds light on the design of chiral metalloborospherenes.