Manipulating Electronic Effect of Nitrogen Donor-Based Ligands for Efficient Complexation and Separation of Palladium from Highly Acidic Solution
Nitrogen donor-based ligands are highly promising extractants for palladium separation from high-level liquid waste (HLLW). However, the electronic effect of these ligands, a critical factor influencing their complexation ability with Pd(II), remains largely unexplored. Herein, three picolinamide-ba...
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2025-03-01
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| author | Yuyang Gan Yimin Cai Song Huang Xiaowei Li Wen Feng Lihua Yuan |
| author_facet | Yuyang Gan Yimin Cai Song Huang Xiaowei Li Wen Feng Lihua Yuan |
| author_sort | Yuyang Gan |
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| description | Nitrogen donor-based ligands are highly promising extractants for palladium separation from high-level liquid waste (HLLW). However, the electronic effect of these ligands, a critical factor influencing their complexation ability with Pd(II), remains largely unexplored. Herein, three picolinamide-based ligands were designed and synthesized, each featuring substituents with distinct electronic effects at the <i>para</i>-position of the pyridine (electro-donating methoxyl group for L-I, hydrogen for L-II, and electro-withdrawing ester group for L-III). The concurrent processes of Pd(II) coordination and ligand protonation enable the manipulation of pyridine nitrogen electronegativity, resulting in a tunable Pd(II) extraction performance. Notably, L-I exhibits the highest extraction efficiency at low acidities (≤1 M HNO<sub>3</sub>) but the lowest extraction at high acidities (≥3 M HNO<sub>3</sub>), whereas L-III shows the poorest efficiency at low acidities but the best performance at high acidities. The Job plot analysis and ESI-HRMS results reveal a 1:1 and 2:1 (L/Pd) stoichiometry in the Pd(II) complexation process. The single crystal X-ray analysis of Pd(NO<sub>3</sub>)<sub>2</sub>(L-II)<sub>2</sub> complex confirms a four-coordinated Pd(II) center, with two pyridine nitrogen atoms and two monodentate nitrate oxygens forming a quadrangular geometry. Density functional theory (DFT) calculations further indicate that the formation of 2:1 (L/Pd) complexes is energetically favored, and the stronger basicity of the nitrogen atoms correlates with a higher Pd(II) binding affinity and increased susceptibility to protonation. |
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| spelling | doaj-art-1cb9dfd3b0d440a297d4284dd83dea1d2025-08-20T02:09:14ZengMDPI AGMolecules1420-30492025-03-01307153310.3390/molecules30071533Manipulating Electronic Effect of Nitrogen Donor-Based Ligands for Efficient Complexation and Separation of Palladium from Highly Acidic SolutionYuyang Gan0Yimin Cai1Song Huang2Xiaowei Li3Wen Feng4Lihua Yuan5College of Chemistry, Key Laboratory of Radiation Physics and Technology of the Ministry of Education, Institute of Nuclear Science and Technology, Sichuan University, Chengdu 610064, ChinaCollege of Chemistry, Key Laboratory of Radiation Physics and Technology of the Ministry of Education, Institute of Nuclear Science and Technology, Sichuan University, Chengdu 610064, ChinaCollege of Chemistry, Key Laboratory of Radiation Physics and Technology of the Ministry of Education, Institute of Nuclear Science and Technology, Sichuan University, Chengdu 610064, ChinaCollege of Chemistry, Key Laboratory of Radiation Physics and Technology of the Ministry of Education, Institute of Nuclear Science and Technology, Sichuan University, Chengdu 610064, ChinaCollege of Chemistry, Key Laboratory of Radiation Physics and Technology of the Ministry of Education, Institute of Nuclear Science and Technology, Sichuan University, Chengdu 610064, ChinaCollege of Chemistry, Key Laboratory of Radiation Physics and Technology of the Ministry of Education, Institute of Nuclear Science and Technology, Sichuan University, Chengdu 610064, ChinaNitrogen donor-based ligands are highly promising extractants for palladium separation from high-level liquid waste (HLLW). However, the electronic effect of these ligands, a critical factor influencing their complexation ability with Pd(II), remains largely unexplored. Herein, three picolinamide-based ligands were designed and synthesized, each featuring substituents with distinct electronic effects at the <i>para</i>-position of the pyridine (electro-donating methoxyl group for L-I, hydrogen for L-II, and electro-withdrawing ester group for L-III). The concurrent processes of Pd(II) coordination and ligand protonation enable the manipulation of pyridine nitrogen electronegativity, resulting in a tunable Pd(II) extraction performance. Notably, L-I exhibits the highest extraction efficiency at low acidities (≤1 M HNO<sub>3</sub>) but the lowest extraction at high acidities (≥3 M HNO<sub>3</sub>), whereas L-III shows the poorest efficiency at low acidities but the best performance at high acidities. The Job plot analysis and ESI-HRMS results reveal a 1:1 and 2:1 (L/Pd) stoichiometry in the Pd(II) complexation process. The single crystal X-ray analysis of Pd(NO<sub>3</sub>)<sub>2</sub>(L-II)<sub>2</sub> complex confirms a four-coordinated Pd(II) center, with two pyridine nitrogen atoms and two monodentate nitrate oxygens forming a quadrangular geometry. Density functional theory (DFT) calculations further indicate that the formation of 2:1 (L/Pd) complexes is energetically favored, and the stronger basicity of the nitrogen atoms correlates with a higher Pd(II) binding affinity and increased susceptibility to protonation.https://www.mdpi.com/1420-3049/30/7/1533nitrogen-based ligandPd(II) complexationelectronic effectsolvent extractionhigh-level liquid waste |
| spellingShingle | Yuyang Gan Yimin Cai Song Huang Xiaowei Li Wen Feng Lihua Yuan Manipulating Electronic Effect of Nitrogen Donor-Based Ligands for Efficient Complexation and Separation of Palladium from Highly Acidic Solution Molecules nitrogen-based ligand Pd(II) complexation electronic effect solvent extraction high-level liquid waste |
| title | Manipulating Electronic Effect of Nitrogen Donor-Based Ligands for Efficient Complexation and Separation of Palladium from Highly Acidic Solution |
| title_full | Manipulating Electronic Effect of Nitrogen Donor-Based Ligands for Efficient Complexation and Separation of Palladium from Highly Acidic Solution |
| title_fullStr | Manipulating Electronic Effect of Nitrogen Donor-Based Ligands for Efficient Complexation and Separation of Palladium from Highly Acidic Solution |
| title_full_unstemmed | Manipulating Electronic Effect of Nitrogen Donor-Based Ligands for Efficient Complexation and Separation of Palladium from Highly Acidic Solution |
| title_short | Manipulating Electronic Effect of Nitrogen Donor-Based Ligands for Efficient Complexation and Separation of Palladium from Highly Acidic Solution |
| title_sort | manipulating electronic effect of nitrogen donor based ligands for efficient complexation and separation of palladium from highly acidic solution |
| topic | nitrogen-based ligand Pd(II) complexation electronic effect solvent extraction high-level liquid waste |
| url | https://www.mdpi.com/1420-3049/30/7/1533 |
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