The structure and desorption properties of the ammines of the group II halides

- The structure of (Mg(NH3)6Cl2, Mg(NH3)6Br2 and Mg(NH3)6I2) are reported.
- Mg(NH3)6X2 shows a monotonic increase in lattice parameters with increasing anion size.
- The desorption properties of Mg(NH3)6X2 are examined by TGA and NMR.
- Decomposition temperature increases with anion size and is independent of Mg-N bonding strength.
- The trends in desorption properties are interpreted using a simple ionic model.

The synthesis of the magnesium halide ammines (Mg(NH3)6Cl2, Mg(NH3)6Br2 and Mg(NH3)6I2) is reported and their structures are identified by high resolution X-ray diffraction. The structures of Mg(NH3)6Br2 and Mg(NH3)6I2 are reported for the first time. The desorption properties of Mg(NH3)6Cl2, Mg(NH3)6Br2 and Mg(NH3)6I2 are examined by thermogravimetric analysis and NMR, and the trends in desorption properties as a function of composition are interpreted using a simple ionic model. It is found that the desorption properties are dependent on the lattice enthalpy of the intermediate and final phases Mg(NH3)2X2, Mg(NH3)X2 and MgX2, that the anion has limited effect on the state of Mg-N bonding and that the desorption temperature of ionic ammines may be tuned by varying the size of the anion.