Unfolding the Extraction and Complexation Behaviors of Trivalent f-Block Elements by a Tetradentate N,O-Hybrid Phenanthroline Derived Phosphine Oxide Ligand

Abstract

In this work, a tetradentate N,O-hybrid 2,9-bis­(diphenylphosphine oxide)-1,10-phenanthroline (Ph2-BPPhen) ligand was studied for the coextraction of trivalent f-block elements from nitric acid media. The extraction as well as the complexation behaviors of Ph2-BPPhen with f-block elements were thoroughly investigated using 31P and 1H NMR spectrometry, UV–vis spectrophotometry, single crystal X-ray diffraction, and density functional theoretical (DFT) calculation. Ph2-BPPhen exhibits remarkably extraction ability for both Am­(III) and Eu­(III) and more than 99.5% of Am­(III) and Eu­(III) were extracted from 1.0 M HNO3 solution. Slope analysis suggests that both 2:1 and 1:1 ligand/metal complexes were probably formed during the extraction. The 1:1 and 2:1 Ln­(III) complexes with Ph2-BPPhen were also identified in CH3OH solution by NMR spectrometry, and the stability constants were determined via UV–vis spectrophotometry. Structures of the 1:1 Eu­(Ph2-BPPhen)­(NO3)3 and Am­(Ph2-BPPhen)­(NO3)3 complexes were further elucidated by single X-ray crystallography and DFT calculations. The higher extractability of Ph2-BPPhen toward trivalent Am­(III) and Eu­(III) compared with the previously reported phenanthroline-derived amide and phosphonate ligands was attributed to the stronger affinity of the −PO­(R)2 group to metal ions. The results from this work indicate that the N,O-hybrid 1,10-phenanthroline derived phosphine oxide ligand can serve as a new and promising candidate for coextraction of trivalent f-block elements in the treatment of nuclear waste.

Preorganization of N,O-hybrid phosphine oxide chelators for effective extraction of trivalent Am/Eu ions – a computational study

“…However, a point by point comprehensive examination on the impact of an N-heterocyclic core (phenanthroline and biphenyl) along with phenyl and pyrrole substitution on the complexation properties of N,O-hybrid phosphine oxide ligands toward trivalent lanthanides and actinides has not yet been carried out. It is important to note that Lei et al demonstrated the usefulness of the phenanthroline-phenyl combination, 38,39 and here we propose three new phosphine oxide ligands with different combinations (Py 2 BPPhen, Ph 2 BPBiphenyl and Py 2 BP-Biphenyl). The substitution of phenyl and pyrrole groups has been shown in the literature to enhance the extraction and complexation ability of organic ligands.…”

“…As 1 : 2 complexes are also possible for these types of ligand, 38,39 a through investigation has been done to throw light on the complexation of these ligands in the ratio of 1 : 2. All the 1 : 2 complexes have been optimized in the solvent phase and their geometries are given in Fig.…”

“…Lei et al in their studies proved that phenylsubstituted moieties helped in the extraction process. 38,39 They performed these studies to increase the basicity of the O donor atoms. However, a point by point comprehensive examination on the impact of an N-heterocyclic core (phenanthroline and biphenyl) along with phenyl and pyrrole substitution on the complexation properties of N,O-hybrid phosphine oxide ligands toward trivalent lanthanides and actinides has not yet been carried out.…”

“…The substitution of phenyl and pyrrole groups has been shown in the literature to enhance the extraction and complexation ability of organic ligands. 2,38 Therefore, we considered these two substituents for this work.…”

Uptake of Am(III) Ions and Eu(III) Ions Using Cyclic Substituted N, O‐hybrid 1,10‐Phenanthroline Derived Phosphine Oxide Ligands ‐ A DFT Exploration

“…Also, it is recognized that the replacement of phosphonate (−P=O(OR) 2 ) groups with phosphine oxide (−P=O(R) 2 ) groups increased the basicity of O donors ligands [19] . Thus they came up with a new and improved N,O‐hybrid 1,10‐phenanthroline derived phosphine oxide ligand (Ph 2 ‐BPPhen) which showed higher complexation and extraction abilities [20] . Although Ph 2 ‐BPPhen showed better features, there is a possibility of tuning its complexion and selectivity through suitable chemical modifications.…”