The electrochemical and spectroelectrochemical
behavior of europium(III)
chloride in a molten salt eutectic, 3LiCl–2KCl, over a temperature
range of 643–1123 K using differential pulse voltammetry, cyclic
voltammetry, potential step chronoabsorptometry, and thin-layer spectroelectrochemistry
is reported. The electrochemical reaction was determined to be the
one-electron reduction of Eu3+ to Eu2+ at all
temperatures. The redox potential of Eu3+/2+ shifts to
more positive potentials, and the diffusion coefficient for Eu3+ increases as temperature increases. The results for the
number of electrons transferred, redox potential, and diffusion coefficient
are in good agreement between the electrochemical and spectroelectrochemical
techniques. This research extends our ability to develop a spectroelectrochemical
sensor for lanthanides and actinides into molten salt media.
The absorption spectra of single-component mixtures of six lanthanide chloride salts were obtained in the molten salt eutectic 3LiCl–2CsCl at 723 K, and used to build multivariate regression models to predict concentrations of multi-component mixtures of these metals in solution.
A series of five new alpha-hydroxy acid-containing chelates inspired by photoactive marine siderophores, along with their Fe(III) complexes, have been synthesized and characterized. These chelates, designated X-Sal-AHA, each contributes a bidentate salicylidene moiety (X-Sal, X = 5-NO(2), 3,5-diCl, H, 3,5-di-tert-butyl, or 3-OCH(3) on the phenolate ring) and a bidentate alpha-hydroxy acid moiety (AHA). The X-ray crystal structure of Na[Fe(3)(3,5-diCl-Sal-AHA)(3)(mu(3)-OCH(3))] shows an Fe(III) trimer with the triply deprotonated, trianionic ligands each spanning two Fe(III)'s that are bridged by the hydroxyl group of the ligand. Additionally, a mu(3)-methoxy anion caps the Fe(III)(3) face. Electrospray ionization mass spectra demonstrate that this structure is representative of the Fe(III) complexes of all five derivatives in methanol solution, with the exception of the X = 3,5-di-t-Bu derivative having a mu(3)-OH bridge rather than a methoxy bridge. Stability constants determined from reduction potentials range from 10(34) for the 5-NO(2) derivative to >10(40) for the 3,5-di-tBu derivative. All five complexes are photoactive when irradiated by sunlight, with the relative rate of photolysis as monitored by Fe(II) transfer correlating with the Hammett sigma(+) parameter for the phenolate ring substituents.
Here we report a technique to perform thin layer spectroelectrochemistry using an aqueous microdrop. The chemical systems used to demonstrate the aqueous microdrop technique were an absorption based ionic probe [Fe(CN)6]3−/4− and an emission based ionic probe [Ru(bpy)3]3+/2+. The ability of the technique to perform semi‐infinite linear diffusion spectroelectrochemistry on an aqueous microdrop has been previously demonstrated; in this work we were able to demonstrate spectroelectrochemical behavior consistent with the restricted diffusion in a thin layer cell by reducing the analyte volume and the optical path length. The thin‐layer diffusion behavior was illustrated by substantial reduction in peak‐to‐peak separations of the cyclic voltammograms and the significant decrease in electrolysis time compared to the semi‐infinite linear diffusion behavior.
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