The impact of alicyclic substituents on the extraction ability of new family of 1,10-phenanthroline-2,9-diamides

Some unexpected “structure–extraction properties” patterns were found for new family of 1,10-phenanthroline-2,9-diamide derived ligands.

Structural Insight into Complexation Ability and Coordination of Uranyl Nitrate by 1,10-Phenanthroline-2,9-diamides

Reprocessing of spent nuclear fuel (SNF) is an important task in a frame of ecology and rational use of natural resources. Uranium, as the main component of SNF (>95%), can be recovered for further use as fresh nuclear fuel. To minimize an amount of solid radioactive waste generated during SNF reprocessing, new extractants are under investigation. Diamides of 1,10-phenanthroline-2,9-dicarboxylic acid are perspective tetradentate N-donor ligands that form strong complexes with f-elements, which are soluble in polar organic solvents. As an example of three ligands of this class, we conducted a comparative study and showed how the substituent in the amide functional group affects the extraction ability toward uranyl nitrate from nitric acid media. We have performed a careful study (NMR, FT-IR, XRD, RMC-EXAFS) of the structures of synthesized complexes of new ligands with uranyl nitrate and used quantum mechanical calculations to explain the discovered regularities through.

3,3-Diazidoenones – new types of highly reactive bis-azides. Preparation and synthetic transformations

A new family of highly reactive 3,3-diazidoenones was obtained. Their chemistry was investigated by both experimental studies and DFT calculations.

Solvation-Anionic Exchange Mechanism of Solvent Extraction: Enhanced U(VI) Uptake by Tetradentate Phenanthroline Ligands

Phenanthroline diamides (L) demonstrated a unique ability to extract uranium from nitric acid solutions into a polar organic solvent forming complexes of 1:2 stoichiometry as tight ion pairs {[UO₂LNO₃]⁺[UO₂(NO₃)₃]^-} by a novel extraction mechanism, which is a combination of two already well-known mechanisms: solvation and ion-pair anion exchange. A UV-vis study was used to confirm the formation of such complexes directly in the organic phase. Moreover, chemical synthesis and single crystal growth were performed to confirm unambiguously the structure of the complexes in the solid state.

4-Oxo-7-fluoro-1,10-phenanthroline-2,9-diamides: Synthesis, Structural Features, Lanthanide Complexes, and Am(III)/Ln(III) Solvent Extraction

A highly efficient synthetic approach was developed for the synthesis of unsymmetrical 1,10-phenanthroline-2,9-diamides with two different substituents in the fourth and seventh positions of the phenanthroline core. The structures of these ligands were confirmed using various spectral methods including 2D-NMR and X-ray analysis. Quantum chemical calculations supported the presence of tautomeric forms of these ligands. Furthermore, it was discovered that these compounds exhibit polydentate ligand behavior toward lanthanide nitrates. The structural characteristics of the complexes formed between these ligands and lanthanide nitrates were investigated both in the solid state and in solution. To further understand the binding properties of these novel unsymmetrical ligands, the binding constants for potential complexes were quantitatively measured by using UV-vis spectrophotometric titration. This allowed for a comprehensive analysis of the binding affinity and stability of these complexes. Extraction experiments of f-elements were performed for symmetrical and unsymmetrical diamides. Overall, this study presents significant advancement in the synthesis and characterization of unsymmetrical 1,10-phenanthroline-2,9-diamides and provides valuable insights into their potential applications as polydentate ligands for lanthanide nitrates.

Pyrrolidine-Derived Phenanthroline Diamides: An Influence of Fluorine Atoms on the Coordination of Lu(III) and Some Other f-Elements and Their Solvent Extraction

Three pyrrolidine-derived phenanthroline diamides were studied as ligands for lutetium trinitrate. The structural features of the complexes have been studied using various spectral methods and X-ray. The presence of halogen atoms in the structure of phenanthroline ligands has a significant impact on both the coordination number of lutetium and the number of solvate water molecules in the internal coordination sphere. The stability constants of complexes with La(NO3)3, Nd(NO3)3, Eu(NO3)3, and Lu(NO3)3 were measured to demonstrate higher efficiency of fluorinated ligands. NMR titration was performed for this ligand, and it was found that complexation with lutetium leads to an approximately 13 ppm shift of the corresponding signal in the 19F NMR spectrum. The possibility of formation of a polymeric oxo-complex of this ligand with lutetium nitrate was demonstrated. Experiments on the liquid–liquid extraction of Am(III) and Ln(III) nitrates were carried out to demonstrate advantageous features of chlorinated and fluorinated pyrrolidine diamides.

Solvent Extraction and Coordination Properties of 1,10-Phenanthroline-2,9-dicarboxylic Acid Diamides with Alkyl-Aryl Substituents toward Lanthanides(III) and Americium(III)

For a wide range of 1,10-phenanthroline-2,9-dicarboxylic acid diamides (DAPhen), differing in the structure of the amide substituent and the presence of chlorine atoms in the 4,7-positions of the phenanthroline core, the extraction properties for lanthanides(III) and americium(III) were studied. Protonation and binding constants to Eu(III) were determined by using UV-vis titration. The values of binding constants and protonation constants are higher for nonsubstituted diamides than for 4,7-chlorinated diamides, which is in good agreement with the solvent extraction data. The structures of more than 20 complexes with lanthanide nitrates in the solid state have been determined using X-ray diffraction analysis. Unusual DAPhen ligand complexes with lanthanum and neodymium nitrates were obtained. For the first time, the possibility of entering a water molecule into the internal coordination sphere of neodymium in a complex with the DAPhen ligand was shown, resulting in the coordination number of neodymium increasing to 11. An unusual complex with a bridge structure was obtained for lanthanum nitrate in which the lanthanum ions have different coordination numbers of 10 and 12.

Influence of Diluent on Extraction Parameters of Systems for Separation Am(III) and Ln(III) Based on 1,10-Phenanthroline-2,9-Diamide

A systematic study of extraction systems for the separation of f-elements using the tetradentate N,O-donor diamide of 1,10-phenanthroline-2,9-dicarboxylic acid (L) in various molecular and ionic solvents was performed. It was demonstrated that the nature of a diluent has a significant impact on solvent extraction of Am(III) and Ln(III) and the stoichiometry of formed complexes with f-elements. The mechanism of complexation and forms of complexes in different diluents were investigated by radiometric methods, UV-vis titration, and XRD.

A Promising 1,3,5-Triazine-Based Anion Exchanger for Perrhenate Binding: Crystal Structures of Its Chloride, Nitrate and Perrhenate Salts

The reaction of pyridine with cyanuric chloride was studied under microwave activation as well as in the presence of silver nitrate. The product of hydrolysis containing two pyridinium rings and chloride anion was isolated. The structures of these anion exchanger salts with chloride, nitrate and perrhenate anions are discussed.

Remarkable Effect of Stereoisomerism on the Am(III)/Ln(III) Solvent Extraction. New Ligands for Highly Efficient Separation of Americium

Two novel 1,10-phenanthroline-2,9-diamide ligands were constructed on the basis of 2-phenylpyrrolidine and obtained as pure diastereomers. These ligands demonstrated advanced properties in liquid-liquid extraction tests. They revealed high efficiency of americium(III) extraction alongside with the record values of selectivity in the separation of americium from light lanthanides from strongly acidic media. An abrupt increase of extraction efficiency when moving along the lanthanide series from lanthanum to lutetium was observed. The examination of the extraction behavior of pure diastereomeric forms revealed noticeable differences in their selectivity while maintaining the overall extraction trend. The explanation of the discovered patterns was elucidated by a comprehensive study of the ability of the ligands to bind lanthanide nitrates in solutions. All the data collected (UV-vis and NMR titration, X-ray analysis of resulting complexes, solvation numbers estimation) were supported by quantum chemical calculation. These data clearly indicated that in the case of light lanthanides the formation of 1 : 1 complexes is most preferable. At the same time, complexes with heavy lanthanides, such as ytterbium and lutetium, exist as ionic pairs which may consist of [L2M]z+ cations counterbalanced by metallate anions, which may result in the formation of the species of unusual composition like L2M2 or even L4M5 clusters.

Steric hindrance of phenanthroline diamides enables a hundredfold increase in Am(III) extraction efficiency

Three novel 1,10-phenanthroline-2,9-dicarboxamides (DAPhen) were prepared and investigated in detail. The presence of alkyl groups in the ortho-positions of the aryl substituent in the ligand amide functions results in completely inhibited rotation around the N-Ar bond and complicated conformational behavior. A very significant effect of ligand steric hindrance on the solvent extraction of lanthanides(III) and Am(III) from nitric acid solution was demonstrated. Extraction tests indicated that all three ligands L1-L3 extract Am better than all lanthanides. Very high separation factors of Am from early lanthanides (La and Ce) SFAm/La,Ce > 40 were observed. For all three ligands, the separation factors from all lanthanides are also high (SFAm/Ln > 10), which makes them suitable for practical applications in spent nuclear fuel (SNF) reprocessing. The extraction efficiency (distribution ratio) increases by almost two orders of magnitude for all tested f-elements while maintaining an overall extraction trend. Since the solvent extraction of Ln(III) and/or Am(III) involves the formation of corresponding complex compounds, a detailed investigation of the coordination chemistry of novel sterically hindered DAPhen ligands toward lanthanides and americium nitrates was performed. A combination of single-crystal X-ray analysis, spectral techniques and quantum-chemical calculations allowed us to explain the nearly hundredfold increase in Am(III) extraction efficiency when moving from ortho-methyl substituents toward more bulky ortho-isopropyl groups.

Competing Routes in the Extraction of Lanthanide Nitrates by 1,10-Phenanthroline-2,9-diamides: An Impact of Structure of Complexes on the Extraction

The fact of the fracture of the extraction curve of lanthanides by 1,10-phenanthroline-2,9-diamides is explained in terms of the structure of complexes, solvent extraction data and quantum chemical calculations. The solvent extraction proceeds in two competing directions: in the form of neutral complexes LLn(NO₃)₃ and in the form of tight ion pairs {[LLn(NO₃)₂ H₂O]⁺ (NO₃^-).

First 24-Membered Macrocyclic 1,10-Phenanthroline-2,9-Diamides-An Efficient Switch from Acidic to Alkaline Extraction of f-Elements

A reaction of acyl chlorides derived from 1,10-phenanthroline-2,9-dicarboxylic acids with piperazine allows the preparation of the corresponding 24-membered macrocycles in good yield. The structural and spectral properties of these new macrocyclic ligands were thoroughly investigated, revealing promising coordination properties towards f-elements (Am, Eu). It was shown that the prepared ligands can be used for selective extraction of Am(III) from alkaline-carbonate media in presence of Eu(III) with an SF_Am/Eu up to 40. Their extraction efficiency is higher than calixarene-type extraction of the Am(III) and Eu(III) pair. Composition of macrocycle-metal complex with Eu(III) was investigated by luminescence and UV-vis spectroscopy. The possibility of such ligands to form complexes of L:Eu = 1:2 stoichiometry is revealed.

4,7-Substituted 1,10-phenanthroline-2,9-dicarboxamides: photophysics of ligands and their complexes with the Eu-Gd-Tb triad

The impact of substituents at the 4- and 7-positions of 1,10-phenanthroline-2,9-dicarboxamides on the photophysical properties of the ligands and their coordination compounds with the lanthanide triad-europium, gadolinium, and terbium-was analyzed. This study demonstrates how modification of the electronic nature of ligands through the incorporation of diverse functional groups affects the luminescence properties of their complexes. The introduction of various substituents leads to the appearance of intra-ligand or ligand-to-ligand charge transfer (CT) states. The highest luminescence efficiency was observed for LH·Eu(NO3)3 (Qin = 54.1% and QL = 9.6%), suggesting strong luminescence quenching of the CT state. It was found that a relatively low ΔE (∼3000 cm-1) supports direct energy transfer from S1 to T1 bypassing the CT state, even though it is outside Reinhoudt's optimal range. The introduction of fluorines leads to the strongest luminescence quenching among all the substituents.