Fe K-Edge XANES and EXAFS of the X-Ray Absorption Spectra of FeCl3 Aqueous Solutions. A Structural Study of the Solute, Iron(III) Chloro Complexes

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Abstract
The Fe K-edge spectra were measured on FeCl3 aqueous solutions by use of synchrotron radiation to reveal the solute structure from the analysis of Fe K-edge EXAFS and XANES. It is concluded that the solute exists mainly as [Fe(H2O)6]3+ but partially as [FeCl(H2O)5]3+ at FeCl3 concentration of 0.1–1 mol dm−3, and it exsits mainly as [FeCl2(H2O)4]+ at the concentration of 3–4 mol dm−3. In the diliquescent product of FeCl3, about a half of the solute is in the state of [FeCl4]− and the remaining half is likely to be in the state of [FeCl2(H2O)4]+. No indication was found for the dimer formation of FeCl3 even in the deliquescent product.