Ab initio molecular dynamics study of the hydrolysis reaction of diborane

Abstract

The hydrolysis reaction of the diborane molecule in aqueous solution has been studied by a series of Car–Parrinello Molecular Dynamics simulations in the Blue Moon Ensemble. The total reaction has been divided into two parts: one dealing with the breaking of B₂H₆ molecule and the formation of a BH₄⁻ ion, a H₂BOH molecule and a H⁺ ion; the second leads to the formation of two hydrogen molecules and another H₂BOH molecule, starting from BH₄⁻, two water molecules and a H⁺ ion. The total reaction studied in this work has been B₂H₆ + 2H₂O → 2H₂BOH + 2H₂. We have described both structurally and electronically the reagents and the products through the radial distribution functions and the Wannier Function Center positions calculations, with attention to the solvent effects on the compounds. The free energy barrier value for the first part of the reaction and a detailed mechanisms for both parts have been reported. An interesting behavior of BH₃ and H₂ molecules in solution has been observed. They form a quite stable three center bond between the electron pair of the hydrogen molecule and the empty orbital of the boron atom in BH₃, which has been described from both a structural and electronic point of view.