NMR studies of the aluminum hydride phases and their stabilities

Abstract

Multinuclear and multidimensional solid state NMR techniques including magic-angle-spinning (MAS) and multiple-quantum (MQ) MAS experiments have been used to characterize various AlH 3 samples. At least three distinct polymorphic AlH 3 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 AlH 3 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 AlH 6 octahedra in the three polymorphs studied. Based on the characteristic NMR signatures determined, phase transition of the γ-AlH 3 to the α-AlH 3 was studied at room and high temperatures. Direct decomposition of the γ-AlH 3 to aluminum metal at room temperature was also unambiguously confirmed by NMR studies.