Mechanochemical Synthesis and Crystal Structure of α‘-AlD3 and α-AlD3

Abstract

AlD₃ was synthesized by ball milling of 3LiAlD₄ + AlCl₃. Planetary ball milling at room temperature resulted in a mixture of AlD₃ (α and α‘) and Al in addition to LiCl, whereas cryomilling at 77 K resulted in only AlD₃ and LiCl. The AlD₃ obtained was a mixture of about ²/₃α and ¹/₃α‘. α‘ was determined by powder neutron diffraction to take the β-AlF₃ structure with space group Cmcm and a = 6.470(3), b = 11.117(5), and c = 6.562(2) Å. It is built up of corner-sharing AlD₆ octahedra in an open structure with hexagonal holes of radius 3.9 Å. α‘ slowly decomposes during storage at 40 °C. α-AlD₃ is also described by a corner-sharing AlD₆ network but in a more dense ReO₃-type arrangement. Both AlD₃ modifications have slightly shorter Al−D distances compared to Na₃AlD₆, Na₂LiAlD₆, and K₂NaAlH₆.