On the geometries, stabilities, and potential energy surfaces of planar C4B2 and C2B4

The geometrical structures, potential energy surfaces, stabilities, and bonding characteristics of low-energy isomers for planar C4B2 and C2B4 are systematically investigated at the CCSD(T)/6-311+G(d)//B3LYP/6-311+G(d) level. Isomers 1a (C2h, 1Ag) and 2a (D2h, 1Ag) with belt-like geometries are the lowest-energy structures of C4B2 and C2B4, respectively, and their structures tend to be similar to those of B6, CB5, and C3B3 clusters. For CxB6-x (x = 1-6) clusters, an interesting planar-to-linear structural transition occurs at x = 1 and 2. The σ-radial, σ-tangential, and delocalized π molecular orbitals are favorable to stabilizing structures of lower-energy isomers of C4B2 and C2B4 based on the NBO and molecular orbital analyses. The lowest-energy isomers of C4B2 and C2B4 are stable both thermodynamically and kinetically at the CCSD(T)/6-311+G(d)//B3LYP/6-311+G(d) level and detectable in experiment, which is significant for future experimental studies of C4B2 and C2B4.