Probing copper-boron interactions in the Cu2B8− bimetallic cluster

Abstract

Borophenes are atom-thin boron layers that can be grown on coinage metal substrates and have become an important class of synthetic 2D nanomaterials. The interactions between boron and substrates are critical to understand the growth mechanisms of borophenes. Here, we report an investigation of copper-boron interactions in the Cu2B8− bimetallic cluster using photoelectron spectroscopy and quantum chemical calculations. Well-resolved photoelectron spectra are obtained at several photon energies and are combined with theoretical calculations to elucidate the structures and bonding of Cu2B8−. Global minimum searches reveal that Cu2B8− consists of a Cu2 dimer atop a B8 molecular wheel with a long Cu–Cu bond length close to that in Cu2+. Chemical bonding analyses indicate that there is clear charge transfer from Cu2 to B8, and the Cu2B8− cluster can be viewed as a [Cu2+]-borozene complex, [Cu2+][B82–]. In the neutral cluster, no Cu–Cu bond exists and Cu2B8 consists of two Cu+ centers interacting with doubly aromatic B82− borozene. The charge transfer interactions between Cu and boron in the Cu2B8− cluster are analogous to charge transfer from the copper substrate to the first borophene layer recently reported to be critical in the growth of bilayer borophenes on a Cu(111) substrate.