Comparative Investigation into the Complexation and Extraction Properties of Tridentate and Tetradentate Phosphine Oxide‐Functionalized 1,10‐Phenanthroline Ligands toward Lanthanides and Actinides
Lei Xu, Yuxun Hao, Yang Xiao, Zhipeng Wang, Chao Xu, Nataliya E. Borisova, Mingze Sun, Xingwang Zhang, Lecheng Lei, Chengliang Xiao
Abstract
Abstract Two new phosphine oxide‐functionalized 1,10‐phenanthroline 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 Eu L 1 (NO 3 ) 3 and [Eu L 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.