Interactions of CyMe4 -BTBP ligand with lanthanides and actinides: Insights from ESI-MS and DFT calculations

Electrospray Ionization Mass Spectrometry (ESI-MS) technique and density functional theory (DFT) calculations were combined to study the formation of the complexes of lanthanides (Ln = La, Ce, Nd, Sm, Eu, Yb) and actinides (UO2 2+ , Th4+ ) with CyMe4 -BTBP (6,6'-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-benzo-[1,2,4-]triazin-3-yl)-[2,2']bipyridine) to understand the mechanisms during the extraction process. Mass spectrometry titrations showed the formation of the complexation in acetonitrile. For lanthanides, only 1:2 complexes ([Ln(L)2 ]3+ , [Ln(L)2 (CH3 CN)]3+ ), [Ln(L)2 (NO3 )]2+ ) were found at low [Ln]/[L] concentration ratios, whereas the 1:1 complexes ([Ln(L)(NO3 )2 ]+ ) were observed when the [Ln]/[L] concentration ratio reached 1.0. For uranyl complexes, 1:1 complex ([UO2 L(NO3 )]+ ) was the only species within the measuring range. Th4+ complexes had two compositions: 1:1 and 1:2, in which 1:2 species was the dominant complex. Collision-induced dissociation (CID) was employed to characterize the fragmentation process. The fragmentation process was unfolded sequentially on both sides of CyMe4 -BTBP ligand with the loss of alkyl groups and cleavage of triazinyl rings. The CID results of CyMe4 -BTBP complexes revealed a slight difference depending on the metal center. The DFT calculations showed that the stable complexes formed in acetonitrile solution were consistent with the ESI-MS results.

Influence of Electronic Modulation of Phenanthroline-Derived Ligands on Separation of Lanthanides and Actinides

The solvent extraction, complexing ability, and basicity of tetradentate N-donor 2,9-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-1,10-phenanthroline (CyMe4-BT- Phen) and its derivatives functionalized by Br, hydroxyphenyl, nitryl were discussed and compared. It was demonstrated that four BTPhen ligands are able to selectively extract Am(lll) over Eu(lll). It was notable that the distribution ratio of 5-nitryl-CyMe4-BTPhen for Eu(lll) was suppressed under 0.02, which was much lower compared to DEu(lll) = 1 by CyMe4-BTPhen. The analysis of the effect of the substituent on the affinity to lanthanides was conducted by UV/vis and fluorescence spectroscopic titration. The stability constants of various ligands with Eu(lll) were obtained by fitting titration curve. Additionally, the basicity of various ligands was determined to be 3.1 ± 0.1, 2.3 ± 0.2, 0.9 ± 0.2, 0.5 ± 0.1 by NMR in the media of CD3OD with the addition of DClO4. The basicity of ligands follows the order of L1 > L2 > L3 > L4, indicating the tendency of protonation decreases with the electron-withdrawing ability increase.

Stability of Different BTBP and BTPhen Extracting or Masking Compounds against γ Radiation

The radiolytic stability of hydrophobic extracting compounds CyMe₄-BTBP and CyMe₄-BTPhen and a hydrophilic masking agent (PhSO₃H)₂-BTPhen, widely employed for trivalent minor actinoid and lanthanoid separation, against γ radiation was tested. Even though the solvent with a promising fluorinated diluent BK-1 provides better extraction properties compared to octan-1-ol, its radiation stability is much lower, and no extraction was observed already after an absorbed dose of 150 kGy (CyMe₄-BTBP) or 200 kGy (CyMe₄-BTPhen). For the (PhSO₃H)₂-BTPhen hydrophilic masking agent, the results showed that the rate of radiolytic degradation was significantly higher in 0.25 M HNO₃ than in 0.5 M HNO₃. For both the hydrophobic and hydrophilic agents, degradation was slower in the presence of both organic and aqueous phases during irradiation.

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.

Exploring the Subtle Effect of Aliphatic Ring Size on Minor Actinide-Extraction Properties and Metal Ion Speciation in Bis-1,2,4-Triazine Ligands

The synthesis and evaluation of three novel bis-1,2,4-triazine ligands containing five-membered aliphatic rings are reported. Compared to the more hydrophobic ligands 1-3 containing six-membered aliphatic rings, the distribution ratios for relevant f-block metal ions were approximately one order of magnitude lower in each case. Ligand 10 showed an efficient, selective and rapid separation of Am^III and Cm^III from nitric acid. The speciation of the ligands with trivalent f-block metal ions was probed using NMR titrations and competition experiments, time-resolved laser fluorescence spectroscopy and X-ray crystallography. While the tetradentate ligands 8 and 10 formed Ln^III complexes of the same stoichiometry as their more hydrophobic analogues 2 and 3, significant differences in speciation were observed between the two classes of ligand, with a lower percentage of the extracted 1:2 complexes being formed for ligands 8 and 10. The structures of the solid state 1:1 and 1:2 complexes formed by 8 and 10 with Y^III , Lu^III and Pr^III are very similar to those formed by 2 and 3 with Ln^III . Ligand 10 forms Cm^III and Eu^III 1:2 complexes that are thermodynamically less stable than those formed by ligand 3, suggesting that less hydrophobic ligands form less stable An^III complexes. Thus, it has been shown for the first time how tuning the cyclic aliphatic part of these ligands leads to subtle changes in their metal ion speciation, complex stability and metal extraction affinity.

Extraction performance of Eu3+ by using heterocyclic N-donor ligands with different structures in ionic liquids: an experimental and theoretical study

Extraction performance of Eu³⁺ has been studied for heterocyclic N-donor ligands with different structures in [C₂mim][NTf₂] as a diluent.

Hydrophilic 2,9-bis-triazolyl-1,10-phenanthroline ligands enable selective Am(iii) separation: a step further towards sustainable nuclear energy

An exciting new family of hydrophilic ligands for the selective extraction of Am(iii) from spent nuclear fuel are reported herein.

4,4′-Di-tert-butyl-6-(1H-tetrazol-5-yl)-2,2′-bipyridine: modification of a highly selective N-donor ligand for the separation of trivalent actinides from lanthanides

In the present work, the complexation and extraction behaviour of HN₄^tbubipy towards An(iii) and Ln(iii) is studied by spectroscopy, solvent extraction, and QM calculations.

Extraction of minor actinides, lanthanides and other fission products by silica-immobilized BTBP/BTPhen ligands

Novel BTBP [bis-(1,2,4-triazin-3-yl)-2,2′-bipyridine]/BTPhen [bis-(1,2,4-triazin-3-yl)-1,10-phenanthroline] functionalized silica gels have been developed to extract minor actinides, lanthanides and other fission products.

Selective separation of americium from europium using 2,9-bis(triazine)-1,10-phenanthrolines in ionic liquids: a new twist on an old story

Am(iii) is efficiently extracted from Eu(iii) in a single contact with a bis(triazine)-1,10-phenanthroline dissolved in an ionic liquid.

The nephelauxetic effect of Eu(iii)–N-donor compounds probed using fluorescence spectroscopy—further evidence for covalence?

A new correlation for the identification of Eu(iii) N-donor complexes in aqueous and organic media is introduced, exhibiting new information on the nature of Eu(iii) bonding.

A closer look on the coordination of soft nitrogen-donor ligands to Cm(iii): SO3-Ph-BTBP

The combination of theory, VSBS and TRLFS revealed new insights into the coordination structure of [Cm(SO₃-Ph-BTBP)₂]⁵⁻.

Exploring electronic effects on the partitioning of actinides(iii) from lanthanides(iii) using functionalised bis-triazinyl phenanthroline ligands

Revealing how soft N-type donor ligands achieve minor actinide selectivity is fundamental in the design of new and improved extractants for advanced future fuel cycles.

Separation and complexation of palladium(ii) with a new soft N-donor ligand 6,6′-bis(5,6-dinonyl-1,2,4-triazin-3-yl)-2,2′-bipyridine (C9-BTBP) in nitric acid medium

Both 1 : 1 and 2 : 1 Pd–C9-BTBP complexes were found in solution by ¹H NMR titration.

Regioselective Synthesis of V-Shaped Bistriazinyl-phenanthrolines

A new, regioselective synthesis of V-shaped 2,9-bis(6-(4-halophenyl)-1,2,4-triazin-3-yl)-1,10-phenanthrolines (4XPhBTPhen) ligands was developed, creating access to a simple and reliable synthesis of precursors for future supramolecular actinide complexing systems. Described is a reactant-directed regioselective synthetic method, which was found to be high yielding and reliable and yields exclusively 6,6'-phenyl BTPhen derivatives (including 4-chloro and 4-bromo) in five simple steps. Molecular and crystal structures of PhBTP and PhBTPhen products are fully determined and both were found to be in space group C2/c. Additionally, molecular and crystal structures of Z and E isomers of 2-hydrazono-2-phenylacetaldehyde oxime, a reagent in the synthetic route, reveal existence of strong intramolecular N-H···O hydrogen bonding in the Z isomer explaining its lower solubility in water.

Influence of the solvent on the complexation of Cm(iii) and Eu(iii) with nPr–BTP studied by time-resolved laser fluorescence spectroscopy

The systematic investigation of the influence of the water content in methanol–water mixtures on the complexation of Cm(iii) and Eu(iii) with nPr–BTP revealed an immense influence of the solvent.

The structures of CyMe4-BTBP complexes of americium(iii) and europium(iii) in solvents used in solvent extraction, explaining their separation properties

The structure around the absorbing atom in the dicomplexes of CyMe₄-BTBP of americium(iii) and europium(III) have been studied in solvent used in solvent extraction.

Effective separation of the actinides Am(iii) and Cm(iii) by electronic modulation of bis-(1,2,4-triazin-3-yl)phenanthrolines

It has been shown that modification of the phenanthroline backbone of CyMe₄-BTPhen leads to subtle electronic modulation, permitting differential ligation of Am(iii) and Cm(iii) resulting in separation factors up to 7.

Probing the difference in covalence by enthalpy measurements: a new heterocyclic N-donor ligand for actinide/lanthanide separation

BQPhen, a new tetra-dentate nitrogen-donor ligand, forms stronger complexes with Am³⁺ than Eu³⁺ or Nd³⁺, due to a more exothermic enthalpy of complexation for the Am³⁺ complexes, implying a higher degree of covalence in the BQPhen complexes with Am³⁺ than Eu³⁺ or Nd³⁺.

TRLFS study on the complexation of Cm(iii) and Eu(iii) with SO3-Ph-BTBP

Cm(iii) and Eu(iii) complexes with SO₃-Ph-BTBP are investigated. The stoichiometry and the conditional stability constants are determined revealing an important influence of the applied medium.