FT-IR Investigation of the State of Iron(III) Chloride Clusters Confined in AOT Reverse Micelles Dispersed in Carbon Tetrachloride

Abstract

The state of the water-soluble salt iron(III) chloride in AOT reverse micelles dispersed in carbon tetrachloride has been investigated by FT-IR spectroscopy. Interestingly, while the entrapment of a lot of water-soluble inorganic salts in AOT reverse micelles requires preliminarily the presence of significant amounts of water within the micellar core, solubilization of FeCl₃ occurs without the need to add water in the micellar solution reaching the very high solubility value, expressed as the maximum salt-to-surfactant molar ratio, of 1.30. The analysis of the spectral features of the investigated samples leads to hypothesize that iron(III) chloride is confined within the reverse micellar core as small size melted clusters of ionic species arising from the reactions

$$ {\text{FeCl}}_{{\text{3}}} + {\text{FeCl}}_{{\text{3}}} \to {\text{FeCl}}^{ + }_{{\text{2}}} + {\text{FeCl}}^{ - }_{{\text{4}}} {\text{ }} $$

$$ {\text{FeCl}}_{{\text{3}}} + {\text{FeCl}}^{ - }_{{\text{4}}} \to {\text{Fe}}_{{\text{2}}} {\text{Cl}}^{ - }_{{\text{7}}} $$

accompanied by a marked structural rearrangement of the AOT head group domain surrounding the micellar core and a shift of the sodium counterion from the micellar core surface to its interior. This picture has been further corroborated by conductivity measurements of FeCl₃/AOT/CCl₄ solutions as a function of the salt-to-surfactant molar ratio.