Spherical Trihedral Metallo-Borospherene with Asymmetric Triangles in Boron Framework

The recent discovery of spherical trihedral metallo-borospherenes Ln₃B₁₈^- (Ln = La, Tb) represents the onset of an unprecedented class of boron-metal binary nanomaterials, where heterogeneous La or Tb atoms, alongside B atoms, constitute integral components of the outer cage surface. Here, C_3v A₁-Sc₃B₁₆⁺ is theoretically predicted as the global minimum by the particle swarm optimization (PSO) algorithm, and its B₁₆-framework comprises unequal B₆ and B₇ triangles, connected by three B atoms between the vertexes of the B₆ triangle and the interval edges of the B₇ triangle. This arrangement forms three equivalent η⁷-B₇ rings, each centered with a Sc atom. The cage surface of the second low-lying A₂ isomer features an asymmetric triangle of B₃ and B₇, along with three B₂-linked units. This configuration gives rise to three equivalent octacoordinated Sc atoms, each centered within η⁸-B₈ rings. These two cationic isomers have been proven to be very stable in kinetics and thermodynamics. Our findings regarding unequal boron triangles and smaller odd-coordinated rings in the B-framework enrich the geometric patterns of trihedral metallo-borospherenes.