Density functional investigation of X@BnHn (X = B+, Be; n = 5–8)

The stability of X@BnHn (X = B+, Be; n = 5–8) is investigated by density functional theory. Geometry optimization shows that both the radius of the center atom and the ring size make contribution to the stability of X@BnHn structure. All the optimized structures are thermodynamics stable according to the large HOMO–LUMO gap, bonding energy, vertical ionization potential and vertical electron affinity. Nuclear independent chemical shift reveals that the (quasi-)planar structures are π aromatic, which is confirmed by chemical bonding analysis.