The σ delocalization in planar boron clusters

The σ delocalization plays an important role in the stability of small boron clusters; therefore, it is important to establish under which circumstances this delocalization contributes to the aromaticity of these molecules. In this work, using electron localization function (ELF) calculations, we show that σ and π electrons follow different patterns of delocalization. For σ electrons the delocalization is mainly due to the p_σ radial overlapping which decreases with ring size, thus, considerable delocalization is expected for small rings, while for the π subsystem, the Hückel rule of organic chemistry works successfully regardless of the cluster size.