Solid solutions of double phosphate hexahydrates in the MgNH4PO4 · 6H2O-Ni2+-H2O system and their dehydration products

Substitutional solid solutions Mg 2+ ↔ Ni 2+ of crystal hydrates Mg (1 − x ) Ni x NH 4 PO 4 · 6H 2 O and Mg (1 − x ) Ni x NH 4 PO 4 · H 2 O (where 0 < x ≤ 0.65), which have struvite structure and dittmarite structure, respectively, have been studied. Ion exchange Mg 2+ ↔ Ni 2+ influences the condition of M 2+ -H 2 O (M 2+ = Mg 2+ , Ni 2+ ) coordination bonds and hydrogen bonds involving coordinated H 2 O molecules, as probed by X-ray powder diffraction, thermal analysis, and FTIR spectroscopy. The coordination of water molecules to metal ions in those crystal hydrates is treated to be a factor that determines the propensity of the resulting crystal structures to polymorphism.