A novel tripodal CMPO ligand: Affinity for f-elements, computational investigations and luminescence properties

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

One of the major challenges in processing rare-earth element (REE) materials arises from the large amounts of radioactive thorium (Th) that are often found within REE minerals, encouraging enhanced metal separation procedures. We report here a study aimed at developing improved systems for REE processing with the goal of efficient extraction of Th(IV) from acidic solution. A tripodal ligand, TRPN-CMPO-Ph, was prepared that utilizes carbamoylmethylphosphine oxide (CMPO) chelators tethered to a tris(3-aminopropyl)amine (TRPN) capping scaffold. The ligand and its metal complexes were characterized by using elemental analysis, NMR, Fourier transform infrared spectroscopy, mass spectrometry, and luminescence spectroscopy. Using a liquid-liquid metal extraction protocol, TRPN-CMPO-Ph selectively extracts Th(IV) at an efficiency of 79% from a mixture of Th(IV), UO22+, and all rare-earth metal cations (except promethium) dissolved in nitric acid into an organic solvent. Th(IV) extraction selectivity is maintained upon extraction from a mixture that approximates a typical monazite leach solution containing several relevant lanthanide ions, including two ions at higher concentration relative to Th(IV). Comparative studies with a tris(2-aminoethyl)amine (TREN)-capped derivative are presented and support the need for a larger TRPN capping scaffold in achieving Th(IV) extraction selectivity.

Understanding the Complexation Behavior of Carbamoylphosphine Oxide Ligands with Representative f-Block Elements

The complexation behavior of carbamoylmethylphosphine oxide ligands (CMPO), a bifunctional phosphine oxide, and their substituted derivatives with Ce(III), Eu(III), Th(IV), U(VI), and Am(III) was probed at the density functional theory (DFT) level. The enhanced extraction of trivalent rare earth elements by the 2-diphenylphosphinylethyl derivative over the conventional CMPO ligand is identified due to the availability of an additional P═O donor group in the former. In addition, the orbital and dispersive interactions play a vital role in the preference of Th(IV) over U(VI) during extraction using CMPO ligands. The better complexing ability of ligands having long alkyl chain substituents at the P atom is justified due to the observed enhanced dispersion interactions in these systems.

Crystal structure of a (carb-oxy-meth-yl)tri-ethyl-aza-nium bromide-2-(tri-ethyl-aza-n-ium-yl)acetate (1/1) hydrogen-bonded dimer

The title compound, C8H18NO2 +·Br-·C8H17NO2, crystallizes as the bromide salt of a 50:50 mixture of (tri-ethyl-azaniumyl)-carb-oxy-lic acid and the zwitterionic (tri-ethyl-azaniumyl)-carboxyl-ate. The two organic entities are linked by a half-occupied bridging carb-oxy-lic acid hydrogen atom that is hydrogen-bonded to the carboxyl-ate group of the second mol-ecule. The tetra-lkyl-ammonium group adopts a nearly perfect tetra-hedral shape around the nitro-gen atom with bond lengths that agree with known values. The carb-oxy-lic acid/carboxyl-ate group is oriented anti to one of the ethyl groups on the ammonium group, and the carbonyl oxygen atom is engaged in intra-molecular C-H⋯O hydrogen bonds.

Accurate Evaluation of Dispersion Energies at Coupled Cluster Level to Understand the Substituent Effects in Am(III) and Eu(III) Complexes

The effect of cyclic and aromatic substituents on the complexation behavior of phosphine oxide ligands with Am(III) and Eu(III) was investigated at density functional theory (DFT) and domain-based local pair natural orbital coupled-cluster (DLPNO-CC) levels. Combining DFT with accurate coupled cluster methods, we have evaluated the dispersion energy contributions to the complexation energies for trivalent Am and Eu complexes for the first time. Irrespective of the nature of substituents on the P atom, the electronic structure of the P═O group remains identical in all of the ligands. The study reveals the importance of dispersion interactions during complexation and is estimated to be more significant for Am(III) than for Eu(III) complexes.

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

This paper describes the synthesis of two beta-phosphorylamide ligands and their coordination chemistry with the Ln ions Tb³⁺, Eu³⁺, and Sm³⁺. Both the ligands and Ln complexes were characterized by IR, NMR, MS, and X-ray crystallography. The luminescence properties of the Tb³⁺ and Eu³⁺ complexes were also characterized, including the acquisition of lifetime decay curves. In the solid state, the Tb³⁺ and Sm³⁺ ligand complexes were found to have a 2:2 stoichiometry when analyzed by X-ray diffraction. In these structures, the Ln ion was bound by both oxygen atoms of each beta-phosphorylamide moiety of the ligands. The Tb³⁺ and Eu³⁺ complexes were modestly emissive as solutions in acetonitrile, with lifetime values that fell within typical ranges.

Supramolecular ligands for the extraction of lanthanide and actinide ions

A selection of supramolecular ligands designed to extract f-elements.

Lanthanide extraction selectivity of a tripodal carbamoylmethylphosphine oxide ligand system

Lanthanide extraction selectivity is attained by variation of the ligand structure and extraction conditions for a series of CMPO-based ligands.

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.

Unique selectivity reversal in Am3+–Eu3+ extraction in a tripodal TREN-based diglycolamide in ionic liquid: extraction, luminescence, complexation and structural studies

A unique selectivity reversal in metal ion extraction was seen in DGA-TREN vis-à-vis T-DGA.

Crystal structures of 1-(4-chloro-phen-yl)-2-(di-phenyl-phosphor-yl)ethan-1-one and 1-(di-phenyl-phosphor-yl)-3,3-di-methyl-butan-2-one

The title compounds, C20H16ClO2P, (I), and C18H21O2P, (II), were synthesized via an Arbuzov reaction between an α-bromo-ketone and isopropoxydi-phenyl-phosphane. In the crystals of both compounds, mol-ecules are linked via bifurcated C-H⋯(O,O) hydrogen bonds, forming chains propagating along [100] for (I) and along [010] for (II). The chains are linked via C-H⋯π inter-actions, leading to the formation of sheets lying parallel to (010) for (I) and (001) for (II). The absolute structure of compound (II) was determined by resonant scattering [Flack parameter = 0.088 (14)].