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: π and σ 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 B₈ fragment, as demonstrated through the energy decomposition analysis.