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

Abstract

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 AmIII and CmIII 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 LnIII 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 YIII, LuIII and PrIII are very similar to those formed by 2 and 3 with LnIII. Ligand 10 forms CmIII and EuIII 1:2 complexes that are thermodynamically less stable than those formed by ligand 3, suggesting that less hydrophobic ligands form less stable AnIII 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.

Selective Separation of Am(III)/Eu(III) by the QL-DAPhen Ligand under High Acidity: Extraction, Spectroscopy, and Theoretical Calculations

“…The extraction of Am(III) and Eu(III) by the QL-DAPhen ligand reaches equilibrium at about 5 min, which is better than that at the equilibrium time of other phenanthroline-based ligands (these ligands reach extraction equilibrium within 20 min) for the extraction of trivalent ions. 26,32,51,52 This difference may be due to the large quinoline group that enables the ligand to have higher preorganization capabilities. At equilibrium, the distribution ratio of Am(III) (D Am = 17) was 2 orders of magnitude larger than that of Eu(III) (D Eu = 0.37), which was roughly equivalent to the previously reported results obtained by the Et-Tol-DAPhen ligand in 3-nitrotrifluorotoluene.…”

Strong Periodic Tendency of Trivalent Lanthanides Coordinated with a Phenanthroline-Based Ligand: Cascade Countercurrent Extraction, Spectroscopy, and Crystallography

“…However, it is extremely difficult to separate Ans­(III) from Lns­(III) efficiently and conveniently. − It is believed that the separation of Lns­(III) and Ans­(III) with specifically designed ligands is an efficient and convenient method. , Researchers have developed a series of ligands and studied their applications in the separation of Lns­(III) and Ans­(III), − such as trialkylphosphine oxide (TRPO), , N,N,N′,N′ -tetraoctyl diglycolamide (TODGA), , and di­(2-ethylhexyl)­phosphoric acid (HDEHP). Due to the demand for the “CHON” principle and high selectivity, nitrogen heterocyclic ligands, ,− such as 2,6-bis­(5,6-dialkyl-1,2,4-triazin-3-yl)-pyridine (BTP), − 6,6′-bis­(5,6-dialkyl-1,2,4-triazin-3-yl)-2,2′-bypyridine (BTBP), , and 2,9-bis­(1,2,4-triazin-3-yl)-1,10-phenanthroline (BTPhen), − are considered to be the most promising ligands for research and application. − Therefore, to design a potential ligand to separate Ans­(III) over Lns­(III) with high efficiency and selectivity, our laboratory has successfully synthesized and characterized a novel lipophilic ligand, Et-Tol-DAPhen, which is applied in the selective separation of actinides over Eu­(III) in a highly acidic environment. − …”

Recent Progress in Trivalent Actinide and Lanthanide Solvent Extraction and Coordination Chemistry with Triazinylpyridine N Donor Ligands

“…85 • Distribution ratios are repressed by electronically modifying the BTPhen, 92,101,[103][104] by adding TEDGA (a competing water soluble ligand), 106 by changing the diluent 99 or using ionic liquids as diluents, 107,111 or by tuning the aliphatic ring size. 95 • Increased Am(III)/Cm(III) selectivity and different intra-Ln(III) selectivity patterns for BTPhen 99 compared to BTBP 12,[112][113] are due to a kinetic effect. Upon extended contacting times, BTPhen show a selectivity similar to BTBP.…”