Actinide-doped boron clusters: from borophenes to borospherenes.

Similar to graphene and fullerene, metal-doping has been considered to be an effective approach to the construction of highly stable boron clusters. In this work, a series of actinide metal-doped boron clusters AnB ₃₆ (An = Pa, Np, Pu, Am, Cm, Bk, and Cf) have been explored using extensive first-principles calculations. We found that the quasi-planar structure of B ₃₆ transforms to an endohedral borospherene An@B ₃₆ after actinide metal doping. Actinoborospherenes exhibit C _2h symmetry with Pa, Np, and Pu dopants and for Am, Cm, Bk and Cf dopants with larger atomic radii, the symmetry of An@B ₃₆ is reduced to C _i . Bonding property analyses such as bond order, molecular orbital (MO) and quantum theory of atoms in molecules (QTAIM) analysis show that the covalency of the An-B bonds in C _2h An@B ₃₆ (An = Pa, Np, and Pu) is higher than that in C _i An@B ₃₆ (An = Am, Cm, Bk, and Cf). These endohedral borospherenes are robust according to thermodynamic and dynamic analyses. As expected, the C _i An@B ₃₆ clusters are less stable compared to C _2h An@B ₃₆ , which is consistent with the stronger covalent bonds of the latter. These results indicate that the existence of the actinide-boron bonding is essential for the high stability of the An@B ₃₆ clusters, confirming that the fullerene-like boron cages can be stabilized by actinide encapsulation. This work is expected to provide potential routes for the construction of robust borospherenes.