Solid phases in the systems glycine–ZnX 2 –H 2 O (X = Cl − , Br − , I − ) at 25 °C

The crystallization in the systems glycine – ZnX 2 – H 2 O (X = Cl − , Br − , I − ) was summarised. Occurrence of both equilibrium and non-equilibrium crystallization was found for these systems. The systems include complex compounds, from which three anhydrous and four hydrate formula types were obtained. The main building units of their crystal structures were mixed electroneutral tetrahedra, isolated in the case of x Gly·ZnX 2 · y H 2 O ( x = 1, 2, 3; y = 0, 1, 2) compounds, or connected in more complex polymer chains in the cases of Gly·ZnX 2 and 2Gly·3ZnI 2 ·4H 2 O. These crystallization processes were explained on the basis of Pearson’s softness–hardness concept and the chemical species existing in the solutions. The study of the system glycine–ZnBr 2 –H 2 O at 25 °C showed the occurrence of equilibrium and non-equilibrium crystallization in it. Three hitherto unknown compounds were obtained, Gly·ZnBr 2 (monoclinic crystal system, space group P 2 1 ), 3Gly·ZnBr 2 (orthorhombic crystal system, space group Pna 2 1 ) and 2Gly·ZnBr 2 ·2H 2 O (monoclinic crystal system, space group C 2/ c ), and characterised by XRD, IR, Raman, and DTA methods. Graphical abstract