Complexation of Light Trivalent Lanthanides with N-(2-Hydroxyethyl)ethylenediamine-N,N′,N′-triacetic Acid in Aqueous Solutions: Thermodynamic Analysis and Coordination Modes

Abstract

N-(2-Hydroxyethyl)ethylenediamine-N,N′,N′-triacetic acid (HEDTA, denoted as H 3 L) is a strong chelating ligand that is widely used in the separation of f elements as relevant to the nuclear fuel cycle. There is much to be known about the structure and composition of the coordination sphere of the complexes of HEDTA with lanthanides. The complexation of HEDTA with light lanthanides (La 3+ , Nd 3+ , and Eu 3+ ) was investigated thermodynamically and structurally in aqueous solutions. Potentiometry and microcalorimetry were performed to acquire the complexation constants (25−70 °C) and enthalpies (25 °C), respectively, at I = 1.0 mol•L −1 NaClO 4 . Coordination modes of the complexes were analyzed by luminescence spectroscopy and NMR spectroscopy. The results indicate that there are two successive Ln 3+ /HEDTA complexes, LnL aq and Ln 2 (H −1 L) 2 2− (Ln 3+ refers to La 3+ , Nd 3+ , and Eu 3+ ; H −1 L 4− refers to deprotonation of the hydroxyl group) during titration. The hydroxyl group of HEDTA is coordinated in the Ln 3+ /HEDTA complex. The dinuclear Ln 2 (H −1 L) 2 2− complex is present as a carboxyl-bridged centrosymmetric dimer, and two carboxyl groups in bridging positions are coordinated to two adjacent Ln 3+ cations. Complexation of NdL aq is exothermic, while formation of the hydrolytic complex Nd 2 (H −1 L) 2 2− is endothermic. Both NdL aq and Nd 2 (H −1 L) 2 2− complexes are driven by entropic force. These data will help to predict the behavior of lanthanides in the separation process, where HEDTA is used as the aqueous complexant.

Complexation of Cyclic Glutarimidedioxime with Cerium: Surrogating for Redox Behavior of Plutonium

“…Parameters such as delivery of titrating volume and electromotive force (EMF, in millivolts) acquisition were controlled by the Tiamo software (version: 2.5). Potentiometric titrations were carried out under magnetic stirring at 25 ± 0.1 °C in a constant temperature cell as described previously. , Argon gas was bubbling to eliminate CO 2 contamination during titration. Multiple potentiometric titrations were performed with different concentrations of Ce 3+ ( C Ce as the total Ce), ligands ( C L for the total ligand concentration), and acidity ( C H for the total concentration of dissociable protons).…”

LUMINESCENT PROPERTIES OF Nd(III) COMPLEXES WITH ETHY­LENE­DIAMINE-N,N'-DISUCCINIC AND N,N-BIS(PHOSPHONO­METHYL)-2-AMINOPROPIONIC ACIDS

“…In addition, for selective binding to various metal ions, ligands must have a heterodentate nature and an unsaturated character [1,2]. These requirements are met by polydentate acyclic ligands, such as aminopolycarboxylic (APС) or aminocarboxyphosphonic (AСPh) acids, which form highly stable metal complexes with lanthanide ions [3][4][5][6][7][8]. Complexes of lanthanides with APC or ACPh that exhibit luminescence in the IR region (Nd, Pr, Er, Yb) can be used as precursors for luminescent diagnostics, for fluorescent immunoassays, for creating amplifiers in laser systems, etc.…”