The structure of zinc chloride complexes in aqueous solution

The structure of zinc chloride complexes with different ratios of chloride to zinc, formed in concentrated ZnCl2 aqueous solutions, were determined from large-angle X-ray scattering using concentrations of the chloride complexes estimated by complementary Raman spectroscopic measurements. The highest chloro complex, [ZnCl4](2-) is tetrahedral with a Zn-Cl bond length of 2.294(4) Angstrom. The trichloro complex, [ZnCl3](-), which coordinates one water molecule, is pyramidal with the Cl-Zn-Cl angle 111 degrees. The Zn-Cl and the Zn-H2O bonds are 2.282(4) and 1.9 Angstrom, respectively. The two lower complexes, [ZnCl2] and [ZnCl](+), cannot be separated by Raman spectra. The average Zn-Cl distance in these complexes is 2.24 Angstrom, and the average Zn-H2O distance is 1.9 Angstrom. In [Zn(H2O)(6)](2+) the Zn-H2O distance is 2.15 Angstrom.