Preferential Coordination of Ammonia to Specific Cations in Mixed Metal Halides

Metal halide-based absorbents of ammonia are promising materials for developing new separation methods for ammonia production. In this study, the ammonia absorption/desorption behaviors of single metal halide salts and mixed metal halides composed of different cations were investigated. The mixed metal halides were prepared via mechanochemical (MC) treatment. The ammonia absorption/desorption behaviors of the MC-treated mixed metal halides were completely different from those of the individual single salts, as well as a simple mixture of the corresponding metal halides prepared using a mortar and pestle. After ammonia absorption, the mixed metal halides formed a single-phase crystal structure with no phase segregation. Fourier-transform infrared analysis revealed that the samples containing specific metal cations (Mn2+) had the same position for the infrared peak (1415 cm–1) assigned to ammonia coordinated to metal cations. These results demonstrate that ammonia preferentially coordinates to specific metal cations (Mn2+) within the mixed metal halides.