Aromaticity of singlet and triplet boron disk-like clusters: A test for electron counting aromaticity rules

Abstract

Boron clusters are polyhedral boron containing structures that have unique features and properties. The disk-like boron clusters are among the most fascinating boron cluster forms. These clusters have a molecular orbital distribution similar to the one derived from the simple particle-on-a-disk model. In this model, the molecular orbitals come by pairs except for m = 0. Disk-like boron clusters in their singlet ground state are aromatic when they reach a closed-shell structure. One could expect that disk-like aromatic boron clusters in the singlet state, when acquiring or releasing two electrons, may be also aromatic in the lowest-lying triplet state. We use magnetically induced current densities and bond current strengths to analyze the aromatic character of a series of disk-like boron clusters. Our results show that, with the exception of triplet 3B19-, the disk-like boron clusters follow Hückel and Baird's rules if one considers the different molecular orbitals grouped by its symmetry. We also found that, if the lowest-lying triplet state in disk-like boron clusters is aromatic, this triplet state is the ground state for this species