Vibrational spectral studies of solutions at elevated temperatures and pressures. 11. A Raman spectral study of aqueous iron(III) chloride solutions between 25 and 300 °C

Abstract

The Raman spectra of acidified aqueous iron(III) chloride solutions have been measured between 25 and 300 °C. When Fe3+ concentrations are in the range 0.75 to 1.0 mol kg−1 and Cl−/Fe3+ ratios, R, in the range 3 to 9.5, the dominant species at 25 °C is trans-[Fe(H2O)4Cl2]+; at 300 °C the sole iron-containing species is tetrahedral [Formula: see text]. Conversion of [Fe(H2O)4Cl2]+ into [Formula: see text] appears not to involve intermediate iron species. In the presence of excess chloride the reaction [Formula: see text] is presumed to occur; ΔH for this reaction has been estimated as +65 ± 8 kJ mol−1. In addition to increasing temperature, factors which favour [Formula: see text] over other iron species include increasing acidity, increasing R, and decreasing dielectric constant. Keywords: high temperature aqueous solutions, iron(III) chloride, Raman spectroscopy.