Deciphering Chemical Bonding in a BC3 Honeycomb Epitaxial Sheet

Abstract

The substitution of every fourth carbon atom in graphene by a boron atom preserves the honeycomb structure in the BC3 two-dimentional lattice, but as we found in our adaptive natural density partitioning analysis, it remarkably alters the chemical bonding. First, in the BC3 lattice, where boron atoms are surrounded by three carbon atoms, carbon forces boron to form two-center–two-electron B–C σ-bonds, while boron is known to participate only in multicenter (three-center–two-electron or four-center–two-electron) σ-bonding in the most stable two-dimensional form of the pure boron lattice, the α-sheet. Second, six-center–two-electron π-bonds found over every hexagon in graphene and in the α-sheet migrate in BC3 to hexagons composed out of carbon atoms only, making π-bonding in those hexagons more similar to the corresponding π-bonding in benzene rather then graphene, leaving hexagons formed by carbon and boron atoms in the BC3 lattice empty without π-bonding. We believe that chemical bonding elements found in our chemical bonding analysis of graphene, the α-sheet of boron, and the BC3 lattice will be useful tools for rationalizing chemical bonding in other two-dimensional boron–carbon materials.