Quantum chemical studies of M(BH4)n and M(AlH4)n, M = Li and Na

The ionic clusters of boron tetrahydride anions (boronhydrides) and aluminum tetrahydride anions (alanate) with Li and Na ions were studied using the ab initio molecular orbital theories. The structures of the clusters of [M(BH4)]n and [M(AlH4)]n (M = Li, Na; n = 1–6) were optimized using the second order Møller–Plesset perturbation theory (MP2) with the aug-cc-pVDZ basis set. The works were extended to the ionic clusters [Mm(XH4)n]+m−n. The stability of these clusters by oxidation (ionization) and by reduction (electron attachment) was also examined. These clusters are found as partial structures of the crystals of M(BH4) and M(AlH4) studied both theoretically and experimentally. Various unique chemical species produced after reduction and oxidation were found as molecular units in the clusters. For instance, Rydberg double anions of (BH4)2− and (AlH4)2− are stable without changing their geometries from the valence-saturated closed shell anions (XH4)−. The molecular units, H2B–H2 and H2Al–H2, are repeatedly found when they are ionized (oxidized) from the parent clusters. The geometric and electronic structures are sometimes drastically deformed from the parents and they might play a role in the decomposition process of the solid materials to produce hydrogen molecules. The anions, [H3XHXH3]− and [H3XH2XH3]−, are also found in the intermediates of the ionization processes.