Structural and thermal gas desorption properties of metal aluminum amides

Abstract

Metal aluminum amides M[Al(NH 2) 4] x ( M = K, Mg, and Ca; x = 1 and 2) were synthesized along with previously reported LiAl(NH 2) 4 and NaAl(NH 2) 4 by ball milling technique under liquid NH 3. The profiles of synchrotron radiation X-ray diffraction suggest that KAl(NH 2) 4, Mg[Al(NH 2) 4] 2 and Ca[Al(NH 2) 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(NH 2) 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 NH 3 below the temperatures of 140 °C during the thermal decomposition and a NH 3 desorption peak temperature ( T des) decreased with the increasing atomic number. Additionally, a relationship between 27Al isotropic chemical shift and T des was discussed. The present study gives an useful information that the thermal stability of the anion complex [Al(NH 2) 4] − can be controlled by a cation M.