Predicting bilayer B50, B52, B56, and B58: structural evolution in bilayer B48-B72 clusters.

The successive experimental observations of planar, cage-like, seashell-like, and bilayer Bn-/0 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 C1 B50 (I), C2h B52 (II), C1 B56 (IV), and C2v B58 (V) as the global minima of the systems to fill in the missing gap in the bilayer B2n series between B48-B72. These highly stable species all contain a B38 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 C1 B50 (I) and C1 B56 (IV) prove to be obviously more stable than the previously reported quasi-planar C2v B50 and C2v B56 with two adjacent B6 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 B2n species in the size range between B48-B72 evolve gradually on the waist around the B38 or elongated B46 bilayer hexagonal prism at the center.