Hydroxyl-group functionalized phenanthroline diimides as efficient masking agents for Am(III)/Eu(III) separation under harsh conditions

Carbon NMR Titration Could Be More Informative for In-Situ Lanthanide Coordination Chemistry Investigation

In situ characterization of coordination species and their evolution are crucial for effective lanthanide separation and recycling. Current technical approaches often operate under constrained conditions, requiring complex equipment, experimental setups, and sometimes intricate data interpretation. Herein, we demonstrate that carbon NMR titrations offer a valuable approach for in situ coordination analysis of lanthanides, particularly for highly fused preorganized ligands that offer more NMR-active carbons than traditional proton NMR. Two representative ligands of both lipophilic and hydrophilic in nature were investigated, and the resulting carbon NMR titration data were analyzed. Comparisons with IR and single-crystal data showed that NMR provided insights not only into the evolution of coordination species but also into changes in the electron distribution during complex formation. Additionally, we discussed inconsistencies between atomic charge populations obtained from carbon NMR and those from Mulliken and Hirshfeld calculations. With advancements in NMR technology and the availability of higher-field NMR instruments, we believe NMR titrations will play an increasingly significant role in unravelling the complex solution coordination chemistry of f-block elements.

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.

Amino Acid Decorated Phenanthroline Diimide as Sustainable Hydrophilic Am(III) Masking Agent with High Acid Resistance

Hydrophilic actinide masking agents are believed to be efficient alternatives to circumvent the extensive hazardous organic solvents/diluents typically employed in the liquid-liquid extraction for nuclear waste management. However, the practical application of hydrophilic ligands faces significant challenges in both synthetic/purification procedures and, more importantly, the acid resistance of the ligands themselves. Herein, we have demonstrated the combination of phenanthroline diimide framework with a biomotif of histidine flanking parts could achieve efficient separation of trivalent lanthanides/actinides (also actinides/actinides) under high acidity of over 1 M HNO3. This approach leverages the soft-hard coordination properties of N, O-hybrid ligands, as well as the energetically favored imides for metal coordination and the multiple protonation of histidine. These factors collectively contribute to the synthesis of an easily accessible, highly water-soluble, superior selective, and acid-resistant Am(III) masking agent. Thus, we have shown in this paper, by proper combination of synthetic N, O-hybrid ligand with amino acid, trivalent lanthanide and actinide separation could be efficiently fulfilled in a more sustainable manner.

Porous crystalline conjugated macrocyclic materials and their energy storage applications

Porous crystalline conjugated macrocyclic materials (CMMs) possess high porosity, tunable structure/function and efficient charge transport ability owing to their planar macrocyclic conjugated π-electron system, which make them promising candidates for applications in energy storage. In this review, we thoroughly summarize the timely development of porous crystalline CMMs in energy storage related fields. Specifically, we summarize and discuss their structures and properties. In addition, their energy storage applications, such as lithium ion batteries, lithium sulfur batteries, sodium ion batteries, potassium ion batteries, Li-CO2 batteries, Li-O2 batteries, Zn-air batteries, supercapacitors and triboelectric nanogenerators, are also discussed. Finally, we present the existing challenges and future prospects. We hope this review will inspire the development of advanced energy storage materials based on porous crystalline CMMs.

Amine-Terminated Phenanthroline Diimides as Aqueous Masking Agents for Am(III)/Eu(III) Separation: An Alternative Ligand Design Strategy for Water-Soluble Lanthanide/Actinide Chelating Ligands

Selective actinide coordination (from lanthanides) is critical for both nuclear waste management and sustainable development of nuclear power. Hydrophilic ligands used as masking agents to withhold actinides in the aqueous phase are currently highly pursued, while synthetic accessibility, water solubility, acid resistance, and extraction capability are the remaining problems. Most reported hydrophilic ligands are only effective at low acidity. We recently proved that the phenanthroline diimide skeleton was an efficient building block for the construction of highly efficient acid-resistant hydrophilic lanthanide/actinide separation agents, while the limited water solubility hindered the loading capability of the ligand. Herein, amine was introduced as the terminal solubilizing group onto the phenanthroline diimide backbone, which after protonation in acid showed high water solubility. The positively charged terminal amines enhanced the ligand water solubility to a large extent, which, on the other side, was believed to be detrimental for the coordination and complexation of the metal cations. We showed that by delicately adjusting the alkyl chain spacing, this intuitive disadvantage could be relieved and superior extraction performances could be achieved. This work holds significance for both hydrophilic lanthanide/actinide separation ligand design and, concurrently, offers insights into the development of water-soluble lanthanide/actinide complexes for biomedical and bioimaging applications.

Complexation and extraction of trivalent actinides over lanthanides using highly soluble phenanthroline diamide ligands with different side chains

Although phenanthroline diamide ligands have been widely reported, their limited solubility in organic solvents and poor performance in the separation of trivalent actinides (An(III)) and lanthanides (Ln(III)) at high acidity are still clear demerits. In this study, we designed and synthesized three highly soluble phenanthroline diamide ligands with different side chains. By introducing alkyl chains and ester groups, the ligands solubility in 3-nitrotrifluorotoluene is increased to over 600 mmol/L, significantly higher than the previous reported phenanthroline diamide ligands. Based on anomalous aryl strengthening, benzene ring was incorporated to enhance ligand selectivity toward Am(III). Extraction experiments demonstrated favorable selectivity of all the three ligands towards Am(III). The optimal separation factor (SFAm/Eu) reaches 53 at 4 mol/L HNO3, representing one of the most effective separation of An(III) over Ln(III) under high acidity. Slope analysis, single crystal structure analysis, as well as titration of ultraviolet visible spectroscopy, mass spectrometry, and nuclear magnetic resonanc confirmed the formation of 1:1 and 1:2 complex species between the metal ions and the ligands depending on the molar ratio of metal ions in the reaction mixture. The findings of this study offer valuable insights for developing phenanthroline diamide ligands for An(III)/Ln(III) separation.

Redox stabilization of Am(v) in a biphasic extraction system boosts americium/lanthanides separation efficiency

Americium (Am) is a key radioactive element in consideration in nuclear waste treatment. Separation of Am from the fission products, lanthanides, is a prerequisite to minimize the hazardous impact of Am and make utilization of rare Am isotopes, but it represents a great challenge due to the chemical similarity between the two groups of elements. Herein, we realize the separation by first oxidizing Am(iii) to high valent Am(vi) and then converting it to Am(v) in situ in a biphasic extraction system with Bi(v) oxidant incorporated in an organic phase. Am(v) is highly stabilized during the separation process and this leads to record high Ln/Am separation factors (>105) in a single contact over a wide range of acidities.