Structure of the nearest surrounding of ions in aqueous solutions of iron(III) chloride by x-ray diffraction method

Abstract

The radial distribution functions of iron(III) chloride aqueous solutions in a wide range of concentrations under ambient conditions have been calculated from the experimental data obtained earlier by X-ray diffraction method. Various models of the structural organization of the systems investigated have been developed. By calculating the theoretical functions for each model and comparing them with the experimental functions, optimal variants have been identified. Quantitative characteristics of the nearest environment structure of Fe3+ and Cl− ions, such as coordination numbers, interparticle distances and varieties of ion pairs, have been determined. It has been found that in a saturated solution of iron(III) chloride the cation coordinates four water molecules at an average distance of 0.210 nm and two chloride ions. As the concentration decreases, the number of solvent molecules in the first coordination sphere of the cation increases to six, and contact ionic associates turn into solvent-separated ion pairs. The Fe3+ ion also forms a second coordination sphere at an average distance of 0.408 nm, the number of H2O molecules in which increases with dilution.