Structural and spectral characterization of the compounds nGly·ZnCl2·mH2O (n = 1,2,3; m = 0,2)

The coordination behaviour of Zn2+ ions in chloride-glycine aqueous solutions and the formation of different complexes were discussed to predict the crystallization of compounds. The crystal structures of three compounds, Gly·ZnCl2, 2Gly·ZnCl2·2H2O and 3Gly·ZnCl2, crystallizing from the above solutions were determined. The data showed the building units of the crystal structures of compounds 2Gly·ZnCl2·2H2O (monoclinic crystal system, space group C2/c) and 3Gly·ZnCl2 (orthorhombic crystal system, space group Pna21) to be discrete distorted electroneutral tetrahedra [Zn(Gly)2Cl2], only differing in the position of Cl− ions (trans or cis), and isolated H2O molecules or Gly zwitterions. Infinite chains of [Zn(Gly)2/2Cl2] tetrahedra build the crystal structure of the compound Gly·ZnCl2 (monoclinic crystal system, space group P21), thus forming a coordination polymer. The Cl− ions are in cis-position and Gly zwitterions are bidentately coordinated to two neighbouring Zn2+ ions, contrary to the monodentate coordination in the previous two structures. The FTIR and FT Raman spectra of all three compounds were recorded and discussed. Their thermal behaviour was also studied, the similarities and differences were explained by the structural features.