Electronic structure, stability, and oxidation of boron-magnesium clusters and cluster solids

Electronic structure studies on MgmBn (-) (1 ≤ n ≤ 15, 0 ≤ m ≤ 3) clusters have been performed to identify the nature of bonding and the origin of stability in the mixed clusters. Boron clusters are found to have planar structures marked by tangential, radial, and π aromaticity. The maximum stability is achieved for when all three types of aromaticity are quenched. The ring like Bn (-) clusters are shown to be electron deficient for n = 6-8, and the addition of Mg atoms is found to enhance the stability of the boron cluster through ionic bonding that quenches the aromaticity and produces umbrella-like structures. Several species including MgB6 (-), MgB8 (-), Mg2B(-), and Mg3B7 (-) are found to have the largest Mg binding energies due to this mechanism. The transfer of a single electron from the Mg atom to the boron cluster results in a Mg atom with a half-filled 3s orbital that may serve as an ignition center for combustion. Studies on the MgB7 and MgB4 cluster solids indicate that they are constructed from icosahedral and umbrella-like motifs and are semiconductors with band gap energies of 1.46 eV and 0.41 eV, respectively.