Solid-Phase Solvate-Free Formation of Magnesium Hydroaluminates Mg(AlH4)2and MgAlH5upon Mechanochemical Activation or Heating of Magnesium Hydride and Aluminum Chloride Mixtures

It is shown that vibromechanically activated or heated magnesium hydride is capable of solid-phase interacting with aluminum chloride to form magnesium tetra- and pentahydroaluminates (Mg(AlH₄)₂and MgAlH₅). When heated above 100°C, Mg(AlH₄)₂undergoes thermolysis (or mechanolysis upon mechanical activation) to form MgAlH₅and AlH₃. The latter liberates aluminum and hydrogen in the moment of isolation. In the 230 to 280°C interval, MgAlH₅also loses reactive AlH₃ . On further heating, the obtained active aluminum and MgH₂give intermetallide Al₂Mg. The ability of Mg(AlH₄)₂to transform into MgAlH₅by the addition of excessive activated MgH₂, as in the case of Sr(AlH₄)₂, is revealed.