Theoretical Modeling of the Structure of Complexes of the Dodecaalane Anion Al12H122− with Borane, Alane, Diborane, and Dialane Molecules

Resumo

The structures, energies, and spectroscopic characteristics of Al₁₂ H₁₂ (L)_n²⁻ complexes with the icosahedral Al₁₂ H₁₂²⁻, 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 H_12-n (BH₄)_n²⁻ and Al₁₂ H_12-n (AlH₄)_n²⁻, 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 H_12-n (AlH₄)_n²⁻ 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.