Lanthanide extraction selectivity of a tripodal carbamoylmethylphosphine oxide ligand system

Abstract

Four tripodal carbamoylmethylphosphine oxide (CMPO)-based ligands are reported here and assessed with regard to lanthanide (Ln) coordination chemistry and selective extraction of lanthanide ions from aqueous solution. Inspired by previous liquid-liquid extraction studies that suggested a preference for terbium(iii), the current work further probes the extraction behavior of a tris-(2-aminoethyl)amine (TREN) capped, ethoxy substituted CMPO ligand with respect to the entire series of lanthanides. Upon confirmation of Tb3+ extraction selectivity versus the whole series, experiments were conducted to assess the effect of increasing the alkyl chain length within the ligand TREN cap, as well as changing the CMPO substituents by replacing the ethoxy groups with more hydrophobic phenyl groups to promote solubility in the organic extraction solvent. Extraction efficiencies remained low for most lanthanides upon increasing the cap size, with %E values consistently around 5%, and a complete loss of Tb3+ preference was noted with a decrease in %E from 18% to 3.5%. For the agent employing the original, smaller TREN cap but with phenyl substituents on the CMPO units, an increase in extraction toward the middle of the row was again observed, albeit modest, with relatively high %E values for both Gd3+ and Tb3+versus the other lanthanides (13 and 11%, respectively). A more dramatic extraction selectivity for the phenyl substituted ligand was achieved upon modification of the ligand to metal ratio, with a 100 : 1 ratio resulting in a near linear decrease in %E from 41% for La3+ to 3.7% for Lu3+. Finally, modification of the TREN capping scaffold by adding an oxygen atom to the central nitrogen led to consistently low %E values, revealing the effect of TREN cap oxidation on Ln extraction for this tripodal CMPO ligand system.

Selective Recovery of Cerium as High-Purity Oxides via Reactive Separation Using CO2-Responsive Structured Ligands

“…During reactions under higher pH conditions (pH > 7), the CH 2 Cl 2 /water emulsion was found to quickly acidify, presumably due to liberation of acid caused by complex formation (eq , L = ligand). By tightly maintaining the appropriate pH of the emulsion (with NaOH), the time for completion of liquid–liquid extraction decreased to ∼1 h, which is significantly faster than many other reported ligands used in these processes …”

“…In this approach, organic ligands are dissolved in a nonpolar, water-immiscible solvent and are used to separate desired metal ions from aqueous solution. 54,65,66 As expected, when the pH of the aqueous layer was acidic (e.g., pH = 3, 1:1 CH 2 Cl 2 /H 2 O), virtually no extraction from the aqueous to organic layer was observed (<10%) during 24 h. However, as the pH of the solution was raised to pH > 5, as could be found in many secondary resource leachate streams, the ability of 1 to extract Ce increased significantly. At neutral or slightly basic pH values (i.e., pH = 8), 1 extracted 67% of Ce (CH 2 Cl 2 solution) at equilibrium (Figure 3A).…”

“…They are based on TriNOx, ,, hydroxamic acid, and glutarimide-dioxime ligands . Carbamoylmethylphosphine oxide ligands extract moderate amounts of lanthanides in a liquid–liquid extraction system under highly acidic conditions . Finally, it has been shown that heptadentate Schiff-base ligands selectively crystallize Dy in the presence of Nd. , While these alternative ligands are often tunable and can provide high specificity, they often require a number of steps for synthesis that utilize pyrophoric reagents and thus are difficult to scale.…”

Two Beta-Phosphorylamide Compounds as Ligands for Sm3+, Eu3+, and Tb3+: X-ray Crystallography and Luminescence Properties

“…The final set of experiments our research group carried out to probe the solution behavior of these Ln-ligand complexes involved the characterization of their luminescence properties. We have previously studied a variety of multipodal ligands bearing this beta-phosphonate/phosphine oxide-amide chelating group, and we have shown that these types of compounds have the ability to sensitize the luminescence of Eu 3+ and Tb 3+ [ 32 , 33 , 34 ]. Ligands 1 and 2 described in this paper are also able to sensitize this luminescence, albeit to a modest extent.…”

Selective Liquid–Liquid Extraction of Thorium(IV) from Rare-Earth Element Mixtures

“…29 Recent work in our laboratory has been geared toward developing preorganized, tripodal CMPO-based ligands using a modular synthetic approach that facilitates structural variation to tune the metal extraction selectivity. Since our initial report of enhanced Tb(III) extraction by the tris(2-aminoethyl)amine (TREN)capped TREN-CMPO-OEt ligand (1, Figure 1), 32 additional ligand caps and CMPO substituents have been explored (e.g., 2 and 3, Figure 1), 33,34 revealing relationships between structural variation and metal extraction. This study focuses on a new extraction agent possessing the tris(3-aminopropyl)amine (TRPN) ligand scaffold, TRPN-CMPO-Ph (4, Figure 1), and describes its f-element extraction behavior.…”