New zinc-glycine-iodide complexes as a product of equilibrium and non-equilibrium crystallization in the Gly – ZnI 2 – H 2 O system

Abstract Equilibrium crystallization of two anhydrous complex compounds, [Zn(gly) 2 I 2 ] and [Zn(gly)I 2 ], and non-equilibrium crystallization of the [Zn 3 (H 2 O) 4 (μ-gly) 2 I 6 ] complex have been observed in the Gly – ZnI 2 – H 2 O system at 25°C. Different mixed zinc-glycine-iodide-aqua complexes exist in the studied solutions and those with the highest activity are responsible for the crystallization process. The stable [ZnI 2 O 2(2Gly) ] 0 complexes are responsible for the large equilibrium crystallization field of the compound [Zn(gly) 2 I 2 ] (monoclinic system, C 2/ c space group), in whose crystal structure they are incorporated as discrete distorted electroneutral tetrahedra. In zinc-iodide solutions with a low water activity it is more probable that the glycine zwitterions act as bidentate ligands and form polynuclear complexes. We assume the [ZnI 2 O 2(2/2Gly) ] 0 infinite chains build the compound [Zn(gly)I 2 ], for which we have found a narrow equilibrium crystallization field. We have failed to describe the crystal structure of this compound because of its limited stability in the air. Non-equilibrium crystallization of [Zn 3 (H 2 O) 4 (μ-gly) 2 I 6 ] (triclinic system, P -1 space group) was demonstrated, with crystal structure built by trinuclear complexes [ZnI 3 O (1/2Gly) ] [ZnO 4(4H2O) O 2(2/2Gly)(trans) ][ZnI 3 O (1/2Gly) ]. The FTIR and Raman spectra and also the thermal behaviour of the three compounds were discussed.