1,10‐Phenanthroline and Non‐Symmetrical 1,3,5‐Triazine Dipicolinamide‐Based Ligands For Group Actinide Extraction

Theoretical unraveling of the separation of trivalent Am and Eu ions by phosphine oxide ligands with different central heterocyclic moieties

The treatment of nuclear spent fuels, especially the separation of minor actinides, is an imperative task for the healthy development of the nuclear industry. Up to now, it still remains a worldwide challenge to separate trivalent An³⁺ from Ln³⁺ because of their similar chemical properties. Therefore, investigating the mechanism behind the selective extraction of An³⁺ by theoretical methods is necessary. In this work, three phosphine oxide ligands with the same side structures but different bridging frameworks, Ph₂PyPO, Ph₂BipyPO and Ph₂PhenPO, were investigated theoretically, and compared with each other using relativistic density functional theory. The results of QTAIM and MBO suggest that the Am-N bonds in the studied complexes have more covalent character than those in the Eu-N bonds, whereas the PDOS analysis indicates that more overlap exists between Am-5f and the Ph₂PyPO's N-2p orbital than between Am-5f and Ph₂BipyPO's N-2p, and Am-5f and Ph₂PhenPO's N-2p orbital. However, the studied ligands all possess stronger affinities towards Am³⁺ than Eu³⁺, which partly results in the Am³⁺ selectivity towards Eu³⁺ in these three ligands. The calculated reaction free energy can reproduce the Am/Eu separation ability difference of three ligands well. This work offers some useful information for An/Ln separation of phosphine oxide ligands, and may help to design more efficient An³⁺/Ln³⁺ separation ligands.

Comparative Investigation into the Complexation and Extraction Properties of Tridentate and Tetradentate Phosphine Oxide-Functionalized 1,10-Phenanthroline Ligands toward Lanthanides and Actinides

Two new phosphine oxide-functionalized 1,10-phenanthroline ligands, tetradentate 2,9-bis(butylphenylphosphine oxide)-1,10-phenanthroline (BuPh-BPPhen, L¹ ) and tridentate 2-(butylphenylphosphine oxide)-1,10-phenanthroline (BuPh-MPPhen, L² ), were synthesized and studied comparatively for their coordination with trivalent actinides and lanthanides. The complexation mechanisms of these two ligands toward trivalent f-block elements were thoroughly elucidated by NMR spectroscopy, UV/vis spectrophotometry, fluorescence spectrometry, single-crystal X-ray diffraction, solvent extraction, and theoretical calculation methods. NMR titration results demonstrated that 1 : 1 and 1 : 2 (metal to ligand) lanthanides complexes formed for L¹ , whereas 1 : 1, 1 : 2 and 1 : 3 lanthanide complexes formed for L² in methanol. The formation of these species was validated by fluorescence spectrometry, and the corresponding stability constants for the complexes of Nd^III with L¹ and L² were determined by using UV/vis spectrophotometry. Structures of the 10-coordinated 1 : 1-type complexes of EuL¹ (NO₃ )₃ and [EuL² (NO₃ )₃ (H₂ O)] Et₂ O in the solid state were characterized by X-ray crystallography. In solvent-extraction experiments, L¹ exhibited extremely strong extraction ability for both Am^III and Eu^III , whereas L² showed nearly no extraction toward Am^III or Eu^III due to its high hydrophilicity. Finally, the structures and bonding natures of the complex species formed between Am^III /Eu^III and L¹ /L² were analyzed in DFT calculations.

Influence of a N-Heterocyclic Core on the Binding Capability of N,O-Hybrid Diamide Ligands toward Trivalent Lanthanides and Actinides

N,O-hybrid diamide ligands with N-heterocyclic skeletons are one of the promising extractants for the selective separation of actinides over lanthanides in a highly acidic HNO₃ solution. In this work, three hard-soft donor mixed diamide ligands, pyridine-2,6-diylbis(pyrrolidin-1-ylmethanone) (Pyr-PyDA), 2,2'-bipyridine-6,6'-diylbis(pyr-rolidine-1-ylmethanone) (Pyr-BPyDA), and (1,10-phenanthroline-2,9-diyl)bis(pyrrolidin-1-ylmethanone) (Pyr-DAPhen), were synthesized and used to probe the influence of N-heterocyclic cores on the complexation and extraction behaviors with trivalent lanthanides and actinides. ¹H NMR titration experiments demonstrated that 1:1 metal-to-ligand complexes were mainly formed between the three ligands and lanthanides, but 1:2 type complexes were also formed between tridentate Pyr-PyDA and Lu(III). The stability constants (log β) of these three ligands with two typical lanthanides, Nd(III) and Eu(III), were determined through spectrophotometric titration. It is found that Pyr-DAPhen formed the most stable complexes, while Pyr-PyDA formed the most unstable complexes with lanthanides, which coincided well with the following solvent extraction results. The solid-state structures of 1:1 type complexes of these three ligands with La(III), Nd(III), and Er(III) in nitrate media were identified by a single-crystal X-ray diffraction technique. Nd(III) and Er(III) were 10-coordinated with Pyr-PyDA, Pyr-BPyDA, and Pyr-DAPhen via one ligand molecule and three nitrate ions. La(III), because of its larger ionic radius, was 11-coordinated with Pyr-DAPhen through one ligand molecule, three nitrate ions, and one methanol molecule. Solvent extraction experiments showed that the preorganized phenanthroline-derived Pyr-DAPhen had the best extraction performance for trivalent actinide among the three ligands tested. This work provides some experimental insights into the design of more efficient ligands for trivalent actinide separation by adjusting the N-heterocyclic cores.

Quantitative Precipitation of Uranyl or Plutonyl Nitrate with N-(1-Adamantyl)acetamide in Nitric Acid Aqueous Solution

The reactivity of the N-(1-adamantyl)acetamide ligand (L = adam) has been evaluated as precipitating agent for the hexavalent uranyl cation ([U] = 20-60 g L^-1) in concentrated nitric acid aqueous solution (0.5-5 M). It results in the formation of a crystalline complex (UO₂)(adam)₂(NO₃)₂·2(adam) (1), in which the uranyl center is 8-fold coordinated to two chelating nitrate groups and two N-(1-adamantyl)acetamide (= adam) ligands through the oxygen atom of the amide function. Two other noncoordinating adam moieties are also observed in the crystal structure packing and interact through a hydrogen-bond scheme with the uranyl-centered species. A similar molecular assembly has been obtained with the plutonyl(VI) cation, in the complex (PuO₂)(adam)₂(NO₃)₂·2(adam) (2). Precipitation studies indicate high (UO₂)(adam)₂(NO₃)₂·2(adam) formation yields (up to 99%_U for an L/U molecular ratio of 5/1) for HNO₃ concentration in the 0.5-5 M range. However, the precipitation kinetics is rather slow and the reaction is completed after several hours (3-4 h). The calcination of the resulting solid under an air atmosphere led to the formation of the U₃O₈ oxide from 400 °C through a transient phase UO₂ fluorite-type (from 200 °C).

Unraveling the complexation mechanism of actinide(iii) and lanthanide(iii) with a new tetradentate phenanthroline-derived phosphonate ligand

The separation and complexation mechanisms of actinide(iii) and lanthanide(iii) with a new phenanthroline-derived phosphonate ligand were studied experimentally and theoretically.

Ligands for f-element extraction used in the nuclear fuel cycle

This review describes the latest advances regarding the development, modification and application of suitable ligands for the liquid–liquid extraction of actinides and lanthanides from nuclear waste.

Selective separation of trivalent f-ions using 1,10-phenanthroline-2,9-dicarboxamide ligands in ionic liquids

1,10-Phenanthroline-2,9-dicarboxamide complexants decorated with alkyl chains and imidazolium cations have been studied for extraction of trivalent f-ions into imidazolium ionic liquids.

Theoretical insights into the separation of Am(iii) over Eu(iii) with PhenBHPPA

Due to the similar chemical properties of actinides An(iii) and lanthanides Ln(iii), their separation in spent nuclear fuel reprocessing is extremely challenging.

Metal complexes containing natural and and artificial radioactive elements and their applications

Recent advances (during the 2007–2014 period) in the coordination and organometallic chemistry of compounds containing natural and artificially prepared radionuclides (actinides and technetium), are reviewed. Radioactive isotopes of naturally stable elements are not included for discussion in this work. Actinide and technetium complexes with O-, N-, N,O, N,S-, P-containing ligands, as well π-organometallics are discussed from the view point of their synthesis, properties, and main applications. On the basis of their properties, several mono-, bi-, tri-, tetra- or polydentate ligands have been designed for specific recognition of some particular radionuclides, and can be used in the processes of nuclear waste remediation, i.e., recycling of nuclear fuel and the separation of actinides and fission products from waste solutions or for analytical determination of actinides in solutions; actinide metal complexes are also usefulas catalysts forcoupling gaseous carbon monoxide, as well as antimicrobial and anti-fungi agents due to their biological activity. Radioactive labeling based on the short-lived metastable nuclide technetium-99m (^99mTc) for biomedical use as heart, lung, kidney, bone, brain, liver or cancer imaging agents is also discussed. Finally, the promising applications of technetium labeling of nanomaterials, with potential applications as drug transport and delivery vehicles, radiotherapeutic agents or radiotracers for monitoring metabolic pathways, are also described.