Spatial and Electronic Structures of BeB8 and MgB8: How far Does the Analogy Go?

Doping boron clusters with Be and its heavier alkaline-earth congener, Mg, usually leads to complexes of different geometry and electronic structure. In this work we show that both neutral BeB8 and MgB8 exhibit a singlet ground state umbrella-like form. In addition, the stability, electronic structure, and aromaticity of the target molecules are compared. The magnetically induced current densities show that BeB8 and MgB8 are double aromatic systems: pi and sigma electrons induce strong diatropic currents. The current densities induced in the studied complexes are of very similar intensity, but with a different spatial distribution. The differences in the current density patterns observed for BeB8 and MgB8 arise from the very nature of the bonding interactions between the M atom and B-8 fragment, as demonstrated through the energy decomposition analysis.