Predicting bilayer B, B, B, and B: structural evolution in bilayer B-B clusters.

The successive experimental observations of planar, cage-like, seashell-like, and bilayer B clusters in the size range between n = 3-48 well demonstrate the structural diversity and rich chemistry of boron nanoclusters. Based on extensive global minimum search and density functional theory calculations, we predict herein the bilayer C B (I), C B (II), C B (IV), and C B (V) as the global minima of the systems to fill in the missing gap in the bilayer B series between B-B. These highly stable species all contain a B bilayer hexagonal prism at the center, with 2, 2, 3, and 3 effective interlayer B-B σ-bonds formed between inward-buckled atoms on the top and bottom layers, respectively. Our bilayer C B (I) and C B (IV) prove to be obviously more stable than the previously reported quasi-planar C B and C B with two adjacent B hexagonal holes. Detailed bonding analyses indicate that these bilayer clusters follow the universal bonding pattern of σ + π double delocalization, making them three-dimensionally aromatic in nature. The bilayer B species in the size range between B-B evolve gradually on the waist around the B or elongated B bilayer hexagonal prism at the center.