Thermodynamic Insight into the Solvation and Complexation Behavior of U(VI) in Ionic Liquid: Binding of CMPO with U(VI) Studied by Optical Spectroscopy and Calorimetry

Understanding the Complexation of Alkyl-Substituted Nitrilotriacetamides with Uranium: A Study by Absorption Spectroscopy and Microcalorimetry

Complexation thermodynamics of UO22+ ions with a series of alkyl-substituted nitrilotriacetamides (NTA) was investigated by absorption spectroscopy and microcalorimetry. The hexamethyl derivative of NTA (HMNTA) forms the weakest two successive complexes with UO22+ ions with stability constants of log β11 = 3.5 ± 0.1 and log β12 = 6.1 ± 0.1. The formation constant values increased linearly with increasing alkyl chain length of the substituents from hexamethyl NTA to hexabutyl NTA (HBNTA) and to hexahexyl NTA (HHNTA). The complexation with each ligand was both enthalpy and entropy driven with exothermic enthalpy changes of ΔH11 = -14.7 ± 1.0 kJ/mol, ΔH12 = -10.2 ± 0.8 kJ/mol for HMNTA, ΔH11 = -19.2 ± 1.2 kJ/mol, ΔH12 = -16.4 ± 1.1 kJ/mol for HBNTA, and ΔH11 = -21.3 ± 1.4 kJ/mol, ΔH12 = -19.4 ± 2.3 kJ/mol for HHNTA. Similarly, the positive entropy changes with each ligand were ΔS11 = 18.1 ± 2.7 J/mol/K, ΔS12 = 82.9 ± 3.8 J/mol/K for HMNTA, ΔS11 = 14.4 ± 1.2 J/mol/K, ΔS12 = 87.2 ± 4.2 J/mol/K for HBNTA, and ΔS11 = 16.1 ± 2.4 J/mol/K, ΔS12 = 92.6 ± 3.1 J/mol/K for HHNTA. Structural features of the complex suggest the participation of two ligands coordinating in a bidentate mode via the carbonyl oxygens. The [UO2L2]2+ complexes appear to be noncentrosymmetric with two ligands and one water molecule occupying the equatorial plane of the dioxo uranyl cation. The structure of the complex was confirmed by 1H NMR titration, EXAFS measurements, and DFT calculations.

Understanding the Interaction of Uranyl Cation with Two C-Pivot Tripodal Amides: Synthesis, Complexation, Microcalorimetry, and DFT Studies

Complexation of uranyl ions with two structurally related C-pivotal tripodal amides with varying spacer lengths, synthesized for the first time, was studied by optical spectroscopy. In the tripodal amides, the coordination was through the carbonyl O atoms where the carbonyl groups were away from the central C-atom by three spacer atoms (LI) and four spacer atoms (LII), respectively. Increasing the spacer atoms going from LI to LII favors the complexation with the linear uranyl cations and results in stronger complex formation. The complexation heat between the uranyl cations and the two amide ligands was directly measured by microcalorimetric titrations. The complexation with both the ligands was driven by exothermic enthalpy and positive entropy changes. Formation of the complex proceeded by the replacement of water molecules from the primary coordination sphere of the uranyl cation. Both ligands formed bisolvated (ML2-type) complexes in which one unit of the ligand binds in a monodentate manner and the other in a bidentate mode. Density functional theory calculations further supported our experimental observations.

Recent Advances in the Study of Trivalent Lanthanides and Actinides by Phosphinic and Thiophosphinic Ligands in Condensed Phases

The separation of trivalent actinides and lanthanides is a key step in the sustainable development of nuclear energy, and it is currently mainly realized via liquid-liquid extraction techniques. The underlying mechanism is complicated and remains ambiguous, which hinders the further development of extraction. Herein, to better understand the mechanism of the extraction, the contributing factors for the extraction are discussed (specifically, the sulfur-donating ligand, Cyanex301) by combing molecular dynamics simulations and experiments. This work is expected to contribute to improve our systematic understanding on a molecular scale of the extraction of lanthanides and actinides, and to assist in the extensive studies on the design and optimization of novel ligands with improved performance.

Isolation of single crystals of a homoleptic UO22+-diglycolamide complex from a room temperature ionic liquid: X-ray crystallography and complexation studies

Complexation and structural investigations of the solid complex of UO22+ ion and TMDGA isolated from an ionic liquid for the first time revealed that the nature and structural features of the complex are identical with those of the complex isolated from the aqueous medium.

Substituent Effect on the Selective Separation and Complexation of Trivalent Americium and Lanthanides by N,O-Hybrid 2,9-Diamide-1,10-phenanthroline Ligands in Ionic Liquid

The extraction and complexation of trivalent americium (Am) and lanthanides (Ln) by four 2,9-diamide-1,10-phenanthroline (DAPhen) ligands with different alkyl substituent groups on the diamide moiety in an ionic liquid (IL), C₄mimNTf₂, were studied through a combination of batch extraction, spectroscopic, and calorimetric approaches. All four DAPhen ligands can achieve selective separation of Am(III) from Eu(III), but the detailed extractability and the extraction kinetics are affected significantly by the length of the alkyl substituent groups. UV-vis absorption spectrophotometric titrations indicate that Ln(III) coordinates with all four ligands in a 1:2 mode in the ionic liquid and the binding strength decreases with the increase of the alkyl chain length. The complexation of the DAPhen ligands with Ln(III) in the ionic liquid is driven by highly positive entropies and opposed by endothermic enthalpies. A luminescence spectroscopy study suggests that each DAPhen ligand coordinates in a tetradentate form with Eu(III). This work further unravels the unique extraction and coordination behavior in an ionic liquid system and offers additional guidelines to design more efficient DAPhen ligands for Ln(III)/An(III) separation.

Coordination of Nd(iii) and Eu(iii) with monodentate organophosphorus ligands in ionic liquids: spectroscopy and thermodynamics

The thermodynamics and coordination nature of the complexes of Ln(iii) with three monodentate organophosphorus ligands in ionic liquids have been elucidated and illustrated by spectroscopic and calorimetric techniques.

Uranium(VI) Complexes with a Calix[4]arene-Based 8-Hydroxyquinoline Ligand: Thermodynamic and Structural Characterization Based on Calorimetry, Spectroscopy, and Liquid-Liquid Extraction

The environmental aspects of ore processing and waste treatment call for an optimization of applied technologies. There, understanding of the structure and complexation mechanism on a molecular scale is indispensable. Here, the complexation of UVI with a calix[4]arene-based 8-hydroxyquinoline ligand was investigated by applying a wide range of complementary methods. In solution, the formation of two complex species was proven with stability constants of log ß1:1=5.94±0.02 and log ß2:1=6.33±0.01, respectively. The formation of the 1:1 complex was found to be enthalpy driven [ΔH1:1=(-71.5±10.0) kJ mol-1; TΔS1:1=(-37.57±10.0) kJ mol-1], whereas the second complexation step was found to be endothermic and entropy driven [ΔH2:1=(32.8±4.0) kJ mol-1; TΔS2:1=(68.97±4.0) kJ mol-1]. Moreover, the molecular structure of [UO2(H6L)(NO3)](NO3) (1) was determined by single-crystal X-ray diffraction. Concluding, radiotoxic UVI was separated from a EuIII-containing solution by the calix[4]arene-based ligand in solvent extractions.

Thermodynamic and spectroscopic study on the solvation and complexation behavior of Ln(iii) in ionic liquids: binding of Ln(iii) with CMPO in C4mimNTf2

Thermodynamics of Ln(iii) complexation with CMPO in “dry” and “wet” ionic liquids reflects how solvation of Ln(iii) affects the complexation and helps identify the extractive species involved in solvent extraction.