Formation of Magnesium and Aluminum Oxides from Water and Metal Hydrides: Creation of the Smallest Ruby

The reaction of water molecules with alane (AlH₃) or magnesium hydride (MgH₂) ultimately produces metal oxide clusters with surrounding hydrogen atoms. This quantum chemical study shows that such reactions proceed initially barrierlessly by creating dative-bonded intermediates, then go through a transition state, where two of the hydrogen atoms come within close proximity of one another, and then eject a hydrogen molecule, producing a strongly favored product. The hydrogen molecule can dissipate the kinetic energy, promoting the formation of the metal hydroxide products as opposed to simply breaking the intermediate apart. This reaction then proceeds consecutively, ultimately producing, in this study, a hydrogenated corundum monomer and hydrogenated periclase dimer, two notable terrestrial minerals. These clusters can likely then react with each other, self-catalyzing a larger reaction network. Such processes may complement or even compete with other means of producing inorganic oxide covalent network molecular clusters or even larger mineral grains.