A bottom-up approach from medium-sized bilayer boron nanoclusters to bilayer borophene nanomaterials.

Inspired by the experimentally observed bilayer B 48 -/0 and theoretically predicted bilayer B 50 -B 72 and based on extensive density functional theory calculations, we report herein a series of novel medium-sized bilayer boron nanoclusters C 1 B 84 (I), C 2 v B 86 (II), C 1 B 88 (III), C 1 B 90 (IV), C 1 B 92 (V), C 1 B 94 (VI), C 2 v B 96 (VII), and C 1 B 98 (VIII) which are the most stable isomers of the systems reported to date effectively stabilized by optimum numbers of interlayer B-B σ bonds between the inward-buckled atoms on top and bottom layers. Detailed bonding analyses indicate that these bilayer species follow the universal bonding pattern of σ + π double delocalization, rendering three-dimensional aromaticity in the systems. More interestingly, the AA-stacked bilayer structural motif in B 96 (VII) with a B 72 bilayer hexagonal prism at the center can be extended to form bilayer C 2 B 128 (IX), D 2 h B 214 (X), C 2 v B 260 (XI), D 2 h B 372 (XII), and D 2 B 828 (XIII) which contain one or multiple conjoined B 72 bilayer hexagonal prisms sharing interwoven zig-zag boron triple chains between them. Such bilayer species or their close-lying AB isomers can be viewed as embryos of the newly reported most stable freestanding BL-α + bilayer borophenes and quasi-freestanding bilayer borophenes on Ag(111) which are composed of interwoven zig-zag boron triple chains shared by conjoined BL B 72 hexagonal prisms, presenting a bottom-up approach from medium-sized bilayer boron nanoclusters to two-dimensional bilayer borophene nanomaterials.