New zinc-glycine-iodide complexes as a product of equilibrium and non-equilibrium crystallization in the Gly - ZnI2 - H2O 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(H2O)(4)(μ-gly)(2)I-6] complex have been observed in the Gly - ZnI2 - H2O 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 [ZnI2O2(2-Gly)](0) complexes are responsible for the large equilibrium crystallization field of the compound [Zn(gly)(2)I-2] (monoclinic system, C2/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 [ZnI2O2(2/2Gly)] 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(H2O)(4)(μ-glY)(2)I-6] (triclinic system, P-1 space group) was demonstrated, with crystal structure built by trinuclear complexes [ZnI3O(1/2Gly)] [ZnO4(4H2O)O2(2/2Gly)(trans)][ZnI3O(1/2Gly)]. The FTIR and Raman spectra and also the thermal behaviour of the three compounds were discussed.