Quasi-planar aromatic B36 and B36− clusters: all-boron analogues of coronene

Abstract

Flat boron has recently emerged as a fascinating concept in cluster science. Here we present computational evidence for the quasi-planar all-boron aromatic B₃₆ (C_6v, ¹A₁) and B₃₆⁻ (C_2v, ²A₁) clusters, established as the global-minimum structures on the basis of Stochastic Surface Walking (SSW) searches. The energetics for low-lying isomeric structures are evaluated using the validated density-functional method at the PBE0/6-311+G* level. Our global-minimum structures are in line with a recent report (Z. A. Piazza et al., Nat. Commun., 2014, 5, 3113). These structures consist of two-dimensional close-packing boron with a perfect hexagonal hole at the center, which may serve as molecular models for the monolayer boron α sheet. Chemical bonding analysis indicates that B₃₆ and B₃₆⁻ are all-boron analogues of coronene (C₂₄H₁₂), featuring concentric dual π aromaticity with an inner π sextet and an outer π sextet. The hydrogenated B₃₆H₆ (C_6v, ¹A₁) model cluster shows similar bonding properties, which possesses concentric triple aromaticity with inner π, outer π, and outer σ sextets.