The chloride ion coordination numbers, obtained from the neutron diffraction experiments of Powell et al.1 on aqueous ZnCl2 solutions, are analyzed assuming inner-sphere complexing of the chloride ion by zinc. Several of the different published sets of stability constants, which describe the equilibria between the various zinc complexes present in solution, are used to determine the mean number of water molecules, x̄, in the complex ClZn(H2O)x̄+. It is shown that, irrespective of the set of stability constants used, x̄ is independent of concentration, within the experimental uncertainty of the neutron data, and takes a value in the range from 3.2 to 3.6. This result implies that the mean number of water molecules displaced from free chloride ions on complexing with Zn2+ is constant and independent of whether the chloride ion is incorporated in the species ZnCl+, ZnCl2, ZnCl3-, or ZnCl42-.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry