Does the length of the alkyl chain affect the complexation and selectivity of phenanthroline-derived phosphonate ligands? – Answers from DFT calculations

Coordination of Fluorine-Substituted 1,10-Phenanthroline Diphosphonates with Americium(III) and Lanthanides(III): Solvent Extraction, Complexation, XRD, and Theoretical Study

Hybrid N,O-donor ligands based on 1,10-phenanthroline are a promising class of compounds for processing high-level waste. Here, we synthesized novel phenanthroline-based diphosphonates containing electron-withdrawing fluorine atoms in alkyl substituents. We studied their extraction properties for Am(III) and, for the first time, for the entire series of lanthanides(III). The extraction of nitric acid for these diphosphonates was also studied. It has been shown that replacing one hydrogen atom with a fluorine atom in the ethyl substituent of a diphosphonate leads to a decrease in the affinity of the ligands for metal cations. Replacing two hydrogen atoms leads to a decrease in the affinity of the ligands for both metal cations and protons. But such modifications led to a change in the nature of the extraction of Am(III) and Eu(III) from nitric acid solutions, and as a result, the diphosphonate with two substituted hydrogen atoms retains its extraction properties when extracted from 5 mol/L HNO3. The complexation in solution was studied by using ultraviolet-visible (UV-vis) titration for Nd(NO3)3 and Eu(NO3)3. The study of complexation in solid form using SC-XRD revealed the formation of complexes of the composition LnL(NO3)3, as well as the possibility of the formation of hydrolyzed binuclear complexes [Eu(μ2,κ4-(RO)2P(O)Phen(O)2(OR))(NO3)2]2. Density functional theory (DFT) calculations were performed to gain more insight into coordination properties and describe experimental data. It was shown that introducing fluorine atoms decreases the charge modules for both Nphen and OP═O and decreases the protonation energy.

Progress in phenanthroline-derived extractants for trivalent actinides and lanthanides separation: where to next?

Spent nuclear fuel (SNF) released from reactors possesses significant radioactivity, heat release properties, and high-value radioactive nuclides. Therefore, using chemical methods for reprocessing can enhance economic efficiency and reduce the potential environmental risks of nuclear energy. Due to the presence of relatively diffuse f-electrons, the chemical properties of trivalent lanthanides (Ln(III)) and actinides (An(III)) in SNF solutions are quite similar. Separation methods have several limitations, including poor separation efficiency and the need for multiple stripping agents. The use of novel multi-dental phenanthroline-derived extractants with nitrogen donor atoms to effectively separate An(III) over Ln(III) has been widely accepted. This review first introduces the development history of phenanthroline-derived extractants for extraction and complexation with An(III) over Ln(III). Then, based on structural differences, these extractants are classified into four categories: nitrogen-coordinated, N,O-hybrid coordinated, highly preorganized structure, and unsymmetric structure. Each category's design principles, extraction, and separation performance as well as their advantages and disadvantages are discussed. Finally, we have summarized and compared the unique characteristics of the existing extractants and provided an outlook. This work may offer a reliable reference for the precise identification and selective separation between An(III) and Ln(III), and point the way for future development and exploration.

Preorganization of N, O-hybrid phosphine oxide chelators for effective extraction of trivalent Am/Eu ions - A computational study

N, O-hybrid phosphine oxide ligands with N-heterocyclic cores are the advanced extractants for extracting actinides over lanthanides. Yet, the challenging task in designing an efficient hybrid ligand is tracing the...

Why trans and not cis? – Molecular Dynamics and DFT study on selective separation of dihaloethene isomers using perethylated pillar[5]arene

The separation of mixtures of isomers is a daunting task. It is found that perethylated pillar[5]arene can separate trans-dichloroethene from its cis isomer. This work deals with the host-guest interactions...