Synthesis of continuous substitutional solid solutions M1−x Ni x (H2PO4)2 · 2H2O with M = Mg, Mn, Co, or Zn

New continuous substitutional solid solutions Mg1−x Ni x (H2PO4)2 · 2H2O, Mn1−x Ni x (H2PO4)2 · 2H2O, Co1−x Ni x (H2PO4)2 · 2H2O, and Zn1−x Ni x (H2PO4)2 · 2H2O (0 ≤ x ≤ 1.00) crystallizing in monoclinic space group P21/n have been synthesized. Their end-member is Ni(H2PO4)2 · 2H2O. Ni(H2PO4)2 · 2H2O is isostructural to magnesium, manganese, iron, cobalt, zinc, and cadmium dihydrogenphosphates. The chemical composition and the unit cell parameters have been determined for the solid solutions. Their IR spectra have been measured.