Theoretical Modeling of the Structure of Complexes of the Dodecaalane Anion Al12H2−12 with Borane, Alane, Diborane, and Dialane Molecules

Abstract

The structures, energies, and spectroscopic characteristics of Al12 H12 (L) 2− complexes with the icosahedral Al12 H 12 2− , dianion sequentially “solvated” with borane, alane, diborane, and dialane molecules (L = BH3, AlH3, B2H6, and Al2H6) have been calculated by the density functional theory method. It has been shown that upon the coordination to the dianion, the BH3 and B2H6 molecules change their configuration and coordinate as bidentate BH4 and B2H7 ligands, while their alane analogues coordinate as monodentate AlH4 and Al2H7 groups to form tetrahydroboranate and tetrahydroalanate complexes like Al12 H12-n (BH4) 2− and Al12 H12-n (AlH4) 2− , respectively. The hydroboranate complexes are stable to decomposition with elimination of a diborane molecule within ∼15−17 kcal/mol for all n values, n = 1−12. Their alanate analogues Al12 H12-n (AlH4) 2− are less stable, but the first members of the series (with n = 2−4) also exhibit noticeable stability to elimination of a dialane molecule within ∼7−10 kcal/mol. Calculations have predicted a possibility of the existence of the most stable of the considered complexes in an isolated state or under matrix isolation conditions. The results can be useful in quantum-chemical modeling of the structure and stability of nanoscale aluminoborohydride compounds with high hydrogen content.