title: New insights into the selectivity of four 1,10-phenanthroline-derived ligands toward the separation of trivalent actinides and lanthanides: a DFT based comparison study.
abstract: Although many heterocyclic N-donor ligands have shown excellent competence for separating actinides from lanthanides, an explanation for why some ligands work whereas others fail is very fundamental but greatly needs to be addressed for designing novel and efficient extractants. In this work, we systematically investigated four phenanthroline-derived ligands, DHDIPhen, BQPhen, Ph2-BTPhen and CyMe4-BTPhen, and their coordination geometrical properties and formation reactions with Am(iii) and Eu(iii) ions by quasi-relativistic density functional theory. The calculated hardness of ligands, which may help to determine their selectivity toward actinides and lanthanides, yielded an order, from the softest to the hardest, as follows: Ph2-BTPhen < CyMe4-BTPhen < BQPhen < DHDIPhen. It shows that the intramolecular hydrogen bonds and size of a ligand cavity are two dominant factors for metal-ion complexation. Natural population analysis (NPA) reveals that the 5d/6d orbitals of Eu/Am accept significantly more electrons than other orbitals, but partial density of states and molecular orbital analysis prove that the d orbitals with more accepted electrons have little contribution to the metal-ligand bonds. The thermodynamic results suggest that ligand protonation does have a great influence on the complexation of ligands with metal ions but does not change the selectivity of ligands toward metal ions. This work can help in-depth understanding the differences of selectivity of various structurally similar ligands and provide more theoretical insights for designing more innovative ligands for Ln/An separation.
authors.affiliation: School of Nuclear Engineering and Geophysics, East China Institute of Technology, Nanchang 330013, China. zhrliu@ecit.cn and Laboratory of Nuclear Energy Chemistry and Key Laboratory for Biomedical Effects of Nanomaterials and Nanosafety, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China. shiwq@ihep.ac.cn.
authors.forename: Han
authors.initials: H
authors.lastname: Wu
authors.affiliation: Laboratory of Nuclear Energy Chemistry and Key Laboratory for Biomedical Effects of Nanomaterials and Nanosafety, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China. shiwq@ihep.ac.cn.
authors.forename: Qun-Yan
authors.initials: QY
authors.lastname: Wu
authors.affiliation: Laboratory of Nuclear Energy Chemistry and Key Laboratory for Biomedical Effects of Nanomaterials and Nanosafety, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China. shiwq@ihep.ac.cn.
authors.forename: Cong-Zhi
authors.initials: CZ
authors.lastname: Wang
authors.affiliation: Laboratory of Nuclear Energy Chemistry and Key Laboratory for Biomedical Effects of Nanomaterials and Nanosafety, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China. shiwq@ihep.ac.cn.
authors.forename: Jian-Hui
authors.initials: JH
authors.lastname: Lan
authors.affiliation: School of Nuclear Engineering and Geophysics, East China Institute of Technology, Nanchang 330013, China. zhrliu@ecit.cn.
authors.forename: Zhi-Rong
authors.initials: ZR
authors.lastname: Liu
authors.affiliation: Laboratory of Nuclear Energy Chemistry and Key Laboratory for Biomedical Effects of Nanomaterials and Nanosafety, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China. shiwq@ihep.ac.cn and School of Radiological and Interdisciplinary Sciences (RAD-X) and Collaborative Innovation Center of Radiation Medicine of Jiangsu Higher Education Institutions, Soochow University, Suzhou 215123, China.
authors.forename: Zhi-Fang
authors.initials: ZF
authors.lastname: Chai
authors.affiliation: Laboratory of Nuclear Energy Chemistry and Key Laboratory for Biomedical Effects of Nanomaterials and Nanosafety, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China. shiwq@ihep.ac.cn.
authors.forename: Wei-Qun
authors.initials: WQ
authors.lastname: Shi