Comparative Investigation into the Complexation and Extraction Properties of Tridentate and Tetradentate Phosphine Oxide‐Functionalized 1,10‐Phenanthroline Ligands toward Lanthanides and Actinides

Abstract

Two new phosphine oxide-functionalized 1,10phenanthroline ligands, tetradentate 2,9-bis (butylphenylphosphine oxide)-1,10-phenanthroline (BuPh-BPPhen, L 1 ) and tridentate 2-(butylphenylphosphine oxide)-1,10-phenanthroline (BuPh-MPPhen, L 2 ), were synthesized and studied comparatively for their coordination with trivalent actinides and lanthanides. The complexation mechanisms of these two ligands toward trivalent f-block elements were thoroughly elucidated by NMR spectroscopy, UV/vis spectrophotometry, fluorescence spectrometry, single-crystal X-ray diffraction, solvent extraction, and theoretical calculation methods. NMR titration results demonstrated that 1 : 1 and 1 : 2 (metal to ligand) lanthanides complexes formed for L 1 , whereas 1 : 1, 1 : 2 and 1 : 3 lanthanide complexes formed for L 2 in methanol. The formation of these species was validated by fluorescence spectrometry, and the corresponding stability constants for the complexes of Nd III with L 1 and L 2 were determined by using UV/vis spectrophotometry. Structures of the 10-coordinated 1 : 1-type complexes of EuL 1 (NO 3 ) 3 and [EuL 2 (NO 3 ) 3 (H 2 O)] Et 2 O in the solid state were characterized by X-ray crystallography. In solvent-extraction experiments, L 1 exhibited extremely strong extraction ability for both Am III and Eu III , whereas L 2 showed nearly no extraction toward Am III or Eu III due to its high hydrophilicity. Finally, the structures and bonding natures of the complex species formed between Am III /Eu III and L 1 /L 2 were analyzed in DFT calculations.

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.…”

Theoretical unraveling of the separation of trivalent Am and Eu ions by phosphine oxide ligands with different central heterocyclic moieties

“…Up to now, many similar phosphine oxide ligands with N-heterocyclic rings have been developed. [17][18][19] The An/Ln separation ability of these new extractants is still not strong, and the extraction kinetics and radio stability properties also need to be optimized. Moreover, the complex mechanism for the An 3+ selectivity of these phosphine oxide ligands and the reason for the difference among the three different N-heterocyclic cores have still not been investigated well.…”

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

“…[12] Therefore N,O-based ligands are preferred to N-based ligands in the SNF treatment. Among them, recently reported N,O-based ligands like Pyr-DAPhen, [13] BuPh-BPPhen, [14] POPhen [15] and Et-Tol-PTA [16] attract a lot of attention since they show tend to show better extraction capabilities.…”