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

Abstract

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

“…In our previous studies, 35,36 we showed that both symmetric 4,7-difluoro-phenanthrolinediamides 1 and asymmetric 4-oxo-7-fluoro-phenanthrolinediamides 2 can be obtained from the 4,7-dichloride precursor 3 (Scheme 1). 36 However, an attempt to obtain fluoro-oxo diamide 2 by fluorination of chloro-oxo diamide 4 was unsuccessful.…”

“…We have already observed this phenomenon earlier and discussed it in detail in one of our previous papers. 36 Complete hydrolysis of both halide atoms at positions 4 and 7 should lead to the formation of molecules with an even greater number of tautomeric forms. We carried out quantum chemical calculations, which showed that the most energetically advantageous form in this case is the oxo-hydroxy form in comparison with the dihydroxy and dioxo forms (Fig.…”

Kinetic features of solvent extraction by N,O-donor ligands of f-elements: a comparative study of diamides based on 1,10-phenanthroline and 2,2′-bipyridine

“…Among N-,O-donor ligands, phenanthroline and bipyridine ligands have been proposed as promising candidates to provide extraction features 19–21 and well-defined structure–property relationships. 22–24…”