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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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new representative DAPhen ligand was synthesized. • A study of DAPhen solvent extraction mechanism of f-elements was carried out. • A mechanism is proposed, taking into account the action of nitric acid. • XRD study reveals structural factors to explain extraction properties. Management of high-level waste is essential for the further sustainable development of nuclear energy. Solvent extraction is one of the technologically acceptable methods for carrying out such processing. The search for new selective extractants is an urgent task that requires systematic research into the structure-properties relationship. 1,10-phenanthroline-2,9-diamides (DAPhen) is a promising ligand class for processing such solutions. Identification of the binding and separation mechanism is the most important fundamental question for any separation system. In this work, we systematically studied of the mechanism of extraction and complex formation by this class of compounds on the example of 4,7-substituted aliphatic 1,10-phenanthroline-2,9-diamides. For systematic comparison, we conducted liquid-liquid extraction studies of f -elements and nitric acid, determination of binding constants (UV–vis and luminescence titration), and structural studies of complexes. Using these methods, it was shown how electron-withdrawing substituents (-Cl) and electron-donating (-OBu) significantly affect the Brønsted and Lewis basicity, the stoichiometry of the complexes formed and the trends in the extraction of f -elements. Moreover, XRD study of an array of complex compounds allowed us to establish the structural features that determine the efficiency and selectivity of liquid-liquid extraction. [ABSTRACT FROM AUTHOR]