Structural and thermal gas desorption properties of metal aluminum amides

Metal aluminum amides M[Al(NH2)4]x (M = K, Mg, and Ca; x = 1 and 2) were synthesized along with previously reported LiAl(NH2)4 and NaAl(NH2)4 by ball milling technique under liquid NH3. The profiles of synchrotron radiation X-ray diffraction suggest that KAl(NH2)4, Mg[Al(NH2)4]2 and Ca[Al(NH2)4]2 have been indexed with single phases, which have never been reported so far. Combination of both FT-IR and 27Al MAS/3QMAS nuclear magnetic resonance suggest that they all have an anion complex unit [Al(NH2)4]− as a basic component, indicating successful synthesis of the metal aluminum amides. Thermogravimetry-differential thermal analysis coupled with mass spectroscopy showed the release of NH3 below the temperatures of 140 °C during the thermal decomposition and a NH3 desorption peak temperature (Tdes) decreased with the increasing atomic number. Additionally, a relationship between 27Al isotropic chemical shift and Tdes was discussed. The present study gives an useful information that the thermal stability of the anion complex [Al(NH2)4]− can be controlled by a cation M.

Research highlights▶ M[Al(NH2)4]x (M = Li, Na, K, Mg, and Ca; x = 1 and 2) were successfully prepared. ▶ The decomposition temperature of M[Al(NH2)4]x is much lower than those of M(NH2)x. ▶ The thermal stability and 27Al chemical shift and χp of M have a correlation. ▶ The thermal stability of M[Al(NH2)4]x can be driven by the choice of the cation M.