New asymmetric tetradentate phenanthroline chelators with pyrazole and amide groups for complexation and solvent extraction of Ln(III)/Am(III)

Haolong Wang; Pengyuan Gao; Tengfei Cui; Dongqi Wang; Jinping Liu; Hui He; Zongyuan Chen; Qiang Jin; Zhijun Guo

doi:10.1039/d3dt03194b

New asymmetric tetradentate phenanthroline chelators with pyrazole and amide groups for complexation and solvent extraction of Ln(III)/Am(III)

Dalton Trans. 2024 Jan 2;53(2):601-611. doi: 10.1039/d3dt03194b.

Authors

Haolong Wang¹, Pengyuan Gao¹, Tengfei Cui¹, Dongqi Wang², Jinping Liu³, Hui He³, Zongyuan Chen¹, Qiang Jin¹, Zhijun Guo¹

Affiliations

¹ Frontier Science Center for Rare Isotopes; School of Nuclear Science and Technology, Lanzhou University, Lanzhou 730000, China. guozhj@lzu.edu.cn.
² State Key Laboratory of Fine Chemicals, Liaoning Key Laboratory for Catalytic Conversion of Carbon Resources, School of Chemical Engineering, Dalian University of Technology, Dalian 116024, China.
³ Radiochemistry Department, China Institute of Atomic Energy, Beijing 102413, China.

PMID: 38063670
DOI: 10.1039/d3dt03194b

Abstract

To tune the complexation and solvent extraction performance of the ligands with a 1,10-phenanthroline core for trivalent actinides (An³⁺) and lanthanides (Ln³⁺), we synthesized two new asymmetric tetradentate ligands with pyrazole and amide groups, i.e., L1 (N,N-diethyl-9-(5-ethyl-1H-pyrazol-3-yl)-1,10-phenanthroline-2-carboxamide) and its analogue L2 with longer alkyl chains (N,N-dihexyl). The complexation of the ligands with Ln³⁺ was confirmed by ¹H NMR titration and X-ray crystallography, and stability constants were measured in methanol by spectrophotometric titration. The asymmetric ligands exhibited an improved performance in terms of selective solvent extraction of Am³⁺ over Eu³⁺ in strongly acidic solutions compared to their symmetric analogues. The improved selectivity of the asymmetric ligands was interpreted theoretically by density functional theory simulations. This study implies that combining different functional groups to construct asymmetric ligands may be an efficient way to tune ligand performance with regard to An³⁺ separation from Ln³⁺.