First 4,7-oxygenated 1,10-phenanthroline-2,9-diamides: synthesis, tautomerism and complexation with REE nitrates.

A new family of phenanthroline ligands was prepared. Hydrolysis of 4,7-dihalogenated 1,10-phenanthroline-2,9-diamides in acidic media leads to the formation of the corresponding 4,7-oxygenated derivatives. These ligands can exist in different tautomeric forms. The tautomerism of 4,7-oxygenated phenanthroline diamides has been investigated using quantum chemical calculations. The unsymmetrical oxo-hydroxy tautomeric form was proved to be the most energetically advantageous according to the spectral data and X-ray analysis. It was shown that 4,7-difluoro derivatives undergo acid hydrolysis more easily when compared to 4,7-dichloro derivatives. The coordination chemistry of 4,7-oxygenated 1,10-phenanthroline-2,9-diamides toward some lanthanide nitrates was investigated. The structures of Ln-complexes thus formed were studied both in the solid state and in solution (XRD analysis and IR, NMR and UV spectroscopy). It was revealed that 4,7-oxygenated ligands adopt the dihydroxy tautomeric form upon coordination with lanthanide nitrates.

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.

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 SFAm/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.

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.

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.

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.

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 Example of Fluorinated Phenanthroline Diamides: Synthesis, Structural Study, and Complexation with Lanthanoids.

An efficient approach to the synthesis of diamides of 4,7-difluoro-1,10-phenanthroline-2,9-dicarboxylic acid was elaborated. Direct nucleophilic substitution with 4,7-dichloro-1,10-phenanthroline precursors opened access to difluoro derivatives in high yield. As a result, four new fluorinated ligands were prepared in up to 88% yield. Their structure was proved by a combination of spectral methods and X-ray data. A set of lanthanoid complexes was prepared to demonstrate the utility of new ligands. The structure of the complexes was studied in solid state (IR-spectroscopy, X-ray diffraction) and in solution (NMR-spectroscopy).

First Trifluoromethylated Phenanthrolinediamides: Synthesis, Structure, Stereodynamics and Complexation with Ln(III).

The first examples of 1,10-phenanthroline-2,9-diamides bearing CF3-groups on the side amide substituents were synthesized. Due to stereoisomerism and amide rotation, such complexes have complicated behavior in solutions. Using advanced NMR techniques and X-ray analysis, their structures were completely elucidated. The possibility of the formation of complex compounds with lanthanoids nitrates was shown, and the constants of their stability are quantified. The results obtained are explained in terms of quantum-chemical calculations.

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

Development of efficient extractants for the separation of actinides and lanthanides in the technologies of nuclear fuel cycle is one of the most urgent and complex tasks in modern nuclear energetics. New family of 4,7-dichloro-1,10-phenanthroline-2,9-dicarboxylic acid diamides based on cyclic amines was synthesized and shown to exhibit high selectivity in the La/Am pair separation (SF (Am/La ≈ 10)) and in the Am/Eu pair separation (SF (Am/Eu ≈ 12)). It was shown that pyrrolidine derived diamide is more efficient extractant for americium, curium and lanthanides from highly acidic HNO3 solution than its non-cyclic N,N,N',N'-tetraalkyl analogues. The structures of synthesized compounds were studied in details by IR, NMR spectroscopy, and single crystal X-ray diffraction. According to spectroscopy data, incorporation of aromatic rings to the amide fragment of ligand leads to complex dynamic behavior in solutions what is believed to strongly affect the extraction ability of synthesized ligands.