Raman Spectral Investigation of the Complex Species of Ferric Chloride in Concentrated Aqueous Solution

Abstract

Raman spectra of concentrated aqueous solutions of ferric chloride were recorded in the spectral range 50 to 500 cm−1. In near-saturated solutions, spectra show a four-line pattern typical of the tetrahedral FeCl4– complex: 390 cm−1 (w); 335 cm−1 (vs, p); 135 cm−1 (w); 110 cm−1 (s). At lower concentrations a new species dominates the spectrum, showing characteristic Raman lines at 318 cm−1 (s, p) and 165 cm−1 (vw). Conventional investigations of spectral changes with concentration of Fe(III) and chloride, coupled with group theoretical arguments, indicate that the stoichiometry of the complex must be FeCl3 or lower. Of the several symmetries that a FeCl3 complex might assume (C2v, C3v, D2h (dimer), and D3h), the D3h trigonal bipyramid structure FeCl3·2H2O with three equatorial chloride ligands and two axial waters is most compatible with the spectral evidence.

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

“…It is fair to say that, despite these advantages, we are not able to significantly improve on the quality of the spectra of Marsten and Bush (8) to in the preamble to the Results and discussion section, the problems of severe band overlapping and absence of standard spectra for many of the femc species likely to be present are not easily overcome. We will refer, where necessary, to these separate room temperature studies and comment upon those aspects of earlier Raman room temperature solution studies which can be corrected in the light of the recent X-ray and glassy state Raman work.…”

“…( 3 , we have utilized Raman spectroscopic methods to study several such systems up to 300°C, with applied pressures up to 9 MPa to maintain the liquid phase (6, 7). We report here the results of a variable temperature investigation of several aqueous ferric chloride systems, between 25 and 300°C.Although earlier workers have used Raman spectroscopy to study similar systems at room temperature (4,8,9) there is still disagreement concerning the interpretation of their results. Indeed such disagreements are not confined to Raman investigations.…”

“…In separate studies, not reported in detail here, we have obtained the Raman spectra of numerous aqueous ferric solutions, at 25°C only, to provide background information for our high temperature work and to see whether advances in equipment (increased sensitivity) and data handling (more secure baseline subtractions and band fitting), coupled with the availability of recent XAFS and XANES results on species populations, enable a more definitive interpretation of such spectra than was possible in earlier studies (4,8,9). It is fair to say that, despite these advantages, we are not able to significantly improve on the quality of the spectra of Marsten and Bush (8) to in the preamble to the Results and discussion section, the problems of severe band overlapping and absence of standard spectra for many of the femc species likely to be present are not easily overcome.…”

“…Although earlier workers have used Raman spectroscopy to study similar systems at room temperature (4,8,9) there is still disagreement concerning the interpretation of their results. Indeed such disagreements are not confined to Raman investigations.…”

Purification of molybdenum trioxide calcine by selective leaching of copper with HCl–NH4Cl

“…There are other issues such as the formation of chloro-complexes at increasing chloride content which affect the solubility of metal ions and kinetics of (Bryce and Berk, 1995;Kimura et al, 1984;Senanayake and Muir, 1988). Using Raman spectroscopy, Marston and Bush (1972) . From the speciation modeling and distribution of these species reported in detail by Kimura et al (1984), Awakura et al (1987) Muir, 1988, 2003 using an overhead stirrer.…”