Unraveling the Coordination Approach of Eu(III) in Cyphos Nitrate Ionic Liquid – A Comprehensive Luminescence Spectroscopy Study

In consideration of the mounting attention of the ionic liquid: Cyphos 101 (trihexyl(tetradecyl)phoshonium chloride: [P66614][Cl]) in the recovery of rare earth and other valuables from their waste matrices, an effort...

On the Coordination Chemistry of the lanthanum(III) Nitrate Salt in EAN/MeOH Mixtures

A thorough structural characterization of the La(NO₃)₃ salt dissolved into several mixtures of ethyl ammonium nitrate (EAN) and methanol (MeOH) with EAN molar fraction χ_EAN ranging from 0 to 1 has been carried out by combining molecular dynamics (MD) and X-ray absorption spectroscopy (XAS). The XAS and MD results show that changes take place in the La³⁺ first solvation shell when moving from pure MeOH to pure EAN. With increasing the ionic liquid content of the mixture, the La³⁺ first-shell complex progressively loses MeOH molecules to accommodate more and more nitrate anions. Except in pure EAN, the La³⁺ ion is always able to coordinate both MeOH and nitrate anions, with a ratio between the two ligands that changes continuously in the entire concentration range. When moving from pure MeOH to pure EAN, the La³⁺ first solvation shell passes from a 10-fold bicapped square antiprism geometry where all the nitrate anions act only as monodentate ligands to a 12-coordinated icosahedral structure in pure EAN where the nitrate anions bind the La³⁺ cation both in mono- and bidentate modes. The La³⁺ solvation structure formed in the MeOH/EAN mixtures shows a great adaptability to changes in the composition, allowing the system to reach the ideal compromise among all of the different interactions that take place into it.

The structural properties of the La(NO₃)₃ salt dissolved into EAN/methanol mixtures were characterized by molecular dynamics and X-ray absorption spectroscopy. The La³⁺ solvation shell undergoes significant changes with increasing the ionic liquid content of the mixture, progressively losing methanol molecules to accommodate more and more nitrate anions. The La³⁺ solvation structure shows great adaptability to composition changes, passing from a 10-fold bicapped square antiprism geometry in pure methanol to a 12-coordinated icosahedral complex in EAN.

Recent Progress in Ionic Liquid Extraction for the Separation of Rare Earth Elements

This review summarizes recent progress in solvent extraction of rare earth elements (REEs) using an ionic liquid (IL) as the extraction solvent. These IL extraction systems are advantageous owing to the affinity of ILs for both charged and neutral hydrophobic species, in contrast to conventional organic solvent extraction systems. Herein, REE extraction studies using ILs are detailed and classified based on the type of extraction system, namely extraction using anionic ligands, extraction using neutral ligands, synergistic extraction, extraction without extractants, and a specific system using task-specific ionic liquids (TSILs). In IL extraction systems, the extracted complexes are often different from those in organic solvent systems, and the REE extraction and separation efficiencies are often significantly enhanced. Synergistic IL extraction is an effective approach to improving the extractability and separability of REEs. The development of novel TSILs suitable for IL extraction systems is also effective for REE separation.

Complexation of 2-thenoyltrifluoroacetone (HTTA) with trivalent f-cations in an ionic liquid: solvent extraction and spectroscopy studies

HTTA forms M(TTA)²⁺, M(TTA)₂⁺, M(TTA)₃° and M(TTA)₄⁻ complexes with lanthanides. Complexation is strongly favoured when the salt of TTA⁻ is used.

Solvation of Zn2+ ion in 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquids: a molecular dynamics and X-ray absorption study

Molecular dynamics simulations and X-ray absorption spectroscopy were employed to study Zn²⁺ ions in [C_nmim][Tf₂N] (n = 2, 4).

The nature of salt effect in enhancing the extraction of rare earths by non-functional ionic liquids: Synergism of salt anion complexation and Hofmeister bias

Separation and recycling of rare-earths using ionic liquids as extractant are becoming a promising approach to replace traditional volatile organic solvents in recent years. Generally, the addition of some special salts could improve the extraction efficiency of rare-earths by numerous non-functional ionic liquids. However, knowledge behind the nature of the salt effect is limited. Here, we found that the enhancement in the extraction of rare-earth ions, Pr³⁺ ions, using non-functional ionic liquid, [A336][NO₃] (Tricaprylmethylammonium nitrate) was driven by the synergism of Hofmeister bias and complexation behaviors of salt anions with Pr³⁺ ions. Molecular dynamic simulations offered a new insight into the interaction mechanism of the ionic liquid with Pr³⁺ ions at liquid/liquid interface. It was revealed that salt anions could perform as a bridge to connect Pr³⁺ ions and the ionic liquid, so that promoted the extraction of Pr³⁺ ions. Therefore, the strong complexation ability of salt anions with Pr³⁺ ions and poor hydration of salt anions faciliated the transport of Pr³⁺ ions across liquid/liquid interface.

Complexation thermodynamics of tetraalkyl diglycolamides with trivalent f-elements in ionic liquids: spectroscopic, microcalorimetric and computational studies

The thermodynamics of lanthanide complexation with DGA ligands was studied in an ionic liquid.

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.

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

The complexation of U(VI) with octylphenyl-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO, denoted as L) in ionic liquid (IL) C₄mimNTf₂ was investigated by UV-vis absorption spectrophotometry and isothermal titration calorimetry. Spectro-photometric titration suggests that three successive complexes, UO₂L_j²⁺ (j = 1-3), formed both in "dry" (water content < 250 ppm) and "wet" (water content ≈ 12 500 ppm) ionic liquid. However, the thermodynamic parameters are distinctly different in the two ILs. In dry IL, the complexation strength between CMPO and U(VI) is much stronger, with stability constants of the respective complexes more than 1 order of magnitude higher than that in wet IL. Energetically, the complexation of U(VI) with CMPO in dry IL is mainly driven by negative enthalpies. In contrast, the complexation in wet IL is overwhelmingly driven by highly positive entropies as a result of the release of a large amount of water molecules from the solvation sphere of U(VI). Moreover, comparisons between the fitted absorption spectra of complexes in wet IL and that of extractive samples from solvent extraction have identified the speciation involved in the extraction of U(VI) by CMPO in ionic liquid. The results from this study not only offer a thermodynamic insight into the complexation behavior of U(VI) with CMPO in IL but also provide valuable information for understanding the extraction behavior in the corresponding solvent extraction system.

Role of Tf2N− anions in the ionic liquid–water distribution of europium(iii) chelates

The replacement of water molecules of [Eu(tta)₃(H₂O)₃] with Tf₂N⁻ was evidenced in water-saturated [C_nmim][Tf₂N] by time-resolved laser-induced fluorescence spectroscopy.

Benzene-centred tripodal diglycolamides for the sequestration of trivalent actinides: metal ion extraction and luminescence spectroscopic investigations in a room temperature ionic liquid

Three benzene-centred tripodal diglycolamide (Bz-T-DGA) ligands were evaluated for actinide ion extraction/complexation in an ionic liquid medium.

Complexation of tetraalkyl diglycolamides with trivalent f-cations in a room temperature ionic liquid: extraction and spectroscopic investigations

This paper reports the complexation of a series of tetraalkyl diglycolamides (TRDGA) with trivalent f-cations in a room temperature ionic liquid,viz. 3-octyl-1-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C₈mim][Tf₂N]).

Highly efficient extraction of actinides with pillar[5]arene-derived diglycolamides in ionic liquids via a unique mechanism involving competitive host–guest interactions

A novel extraction mechanism is described.

Binding of pyrazine-functionalized calix[4]arene ligands with lanthanides in an ionic liquid: thermodynamics and coordination modes

Complexation thermodynamics of Eu³⁺ with pyrazine-functionalized calix[4]arene in ionic liquid was investigated by absorption spectroscopy, luminescence spectroscopy and microcalorimetry.