The B35 Cluster with a Double-Hexagonal Vacancy: A New and More Flexible Structural Motif for Borophene.

Elemental boron is electron-deficient and cannot form graphene-like structures. Instead, triangular boron lattices with hexagonal vacancies have been predicted to be stable. A recent experimental and computational study showed that the B36 cluster has a planar C6v structure with a central hexagonal hole, providing the first experimental evidence for the viability of atom-thin boron sheets with hexagonal vacancies, dubbed borophene. Here we report a boron cluster with a double-hexagonal vacancy as a new and more flexible structural motif for borophene. Photoelectron spectrum of B35− displays a simple pattern with certain similarity to that of B36-. Global minimum searches find that both B35− and B35 possess planar hexagonal structures, similar to that of B36, except a missing interior B atom that creates a doublehexagonal vacancy. The closed-shell B35− is found to exhibit triple n aromaticity with 11 delocalized π bonds, analogous to benzo(g,h,i)perylene (C22H12). The B35 cluster can be used to build atom-thin boron sheets with various hexagonal hole densities, providing further experimental evidence for the viability of borophene. [ABSTRACT FROM AUTHOR]