NMR studies of the aluminum hydride phases and their stabilities

Multinuclear and multidimensional solid state NMR techniques including magic-angle-spinning (MAS) and multiple-quantum (MQ) MAS experiments have been used to characterize various AlH3 samples. At least three distinct polymorphic AlH3 phases have been prepared by desolvating the alane etherate product from its organometallic synthesis. MAS-NMR spectra for the 1H and 27Al nuclei have been obtained on a variety of AlH3 samples that include the β- and γ-phases as well as the α-phase. 27Al MAS NMR was found to respond with high sensitivity for showing differences in spatial arrangements of AlH6 octahedra in the three polymorphs studied. Based on the characteristic NMR signatures determined, phase transition of the γ-AlH3 to the α-AlH3 was studied at room and high temperatures. Direct decomposition of the γ-AlH3 to aluminum metal at room temperature was also unambiguously confirmed by NMR studies.