Influence of a N-Heterocyclic Core on the Binding Capability of N,O-Hybrid Diamide Ligands toward Trivalent Lanthanides and Actinides

Abstract

N,O-hybrid diamide ligands with N-heterocyclic skeletons are one of the promising extractants for the selective separation of actinides over lanthanides in a highly acidic HNO3 solution. In this work, three hard–soft donor mixed diamide ligands, pyridine-2,6-diylbis­(pyrrolidin-1-ylmethanone) (Pyr-PyDA), 2,2′-bipyridine-6,6′-diylbis­(pyr-rolidine-1-ylmethanone) (Pyr-BPyDA), and (1,10-phenanthroline-2,9-diyl)­bis­(pyrrolidin-1-ylmethanone) (Pyr-DAPhen), were synthesized and used to probe the influence of N-heterocyclic cores on the complexation and extraction behaviors with trivalent lanthanides and actinides. 1H NMR titration experiments demonstrated that 1:1 metal-to-ligand complexes were mainly formed between the three ligands and lanthanides, but 1:2 type complexes were also formed between tridentate Pyr-PyDA and Lu­(III). The stability constants (log β) of these three ligands with two typical lanthanides, Nd­(III) and Eu­(III), were determined through spectrophotometric titration. It is found that Pyr-DAPhen formed the most stable complexes, while Pyr-PyDA formed the most unstable complexes with lanthanides, which coincided well with the following solvent extraction results. The solid-state structures of 1:1 type complexes of these three ligands with La­(III), Nd­(III), and Er­(III) in nitrate media were identified by a single-crystal X-ray diffraction technique. Nd­(III) and Er­(III) were 10-coordinated with Pyr-PyDA, Pyr-BPyDA, and Pyr-DAPhen via one ligand molecule and three nitrate ions. La­(III), because of its larger ionic radius, was 11-coordinated with Pyr-DAPhen through one ligand molecule, three nitrate ions, and one methanol molecule. Solvent extraction experiments showed that the preorganized phenanthroline-derived Pyr-DAPhen had the best extraction performance for trivalent actinide among the three ligands tested. This work provides some experimental insights into the design of more efficient ligands for trivalent actinide separation by adjusting the N-heterocyclic cores.

2-Methylpyrrolidine derived 1,10-phenanthroline-2,9-diamides: promising extractants for Am(iii)/Ln(iii) separation

“…It was of particular interest to reveal the effect of the introduction of electron-donor group into the α-position in comparison with the recently studied diamides based on unsubstituted pyrrolidine. 27 Moreover, in this work we also compared the influence of chlorine atoms in positions 4 and 7 of phenanthroline nuclei on the coordination properties towards f-elements.…”

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

“…Synthesis of the “parent” pyrrolidine-derived ligand was first published in 2004 [ 28 ]. Later, some properties of this compound were revealed [ 29 ].…”

New tetradentate N,O-hybrid phenanthroline-derived organophosphorus extractants for the separation and complexation of trivalent actinides and lanthanides

“…Most of the studies closely investigated the influence of the steric hindrance and length of side substituents on the extraction and complexation properties with respect to f-elements. Compared to the insights on controlling side substituents and N-heterocyclic skeletons, 59 we focused on a strategy of adjusting the electronic properties of the closest O atoms to binding centers to improve the separ- ation ability. In this work, a novel phosphine oxide ligand, (1,10-phenanthroline-2,9-diyl)bis(ethyl(phenyl)phosphine oxide) (Et-Ph-BPPhen, L 1 ), was synthesized.…”