Meng Ruixue, Xu Lei, Yang Xiao, Sun Mingze, Xu Chao, Borisova Nataliya E, Zhang Xingwang, Lei Lecheng, Xiao Chengliang
College of Chemical and Biological Engineering, Zhejiang University, Hangzhou 310027, China.
Institute of Zhejiang University-Quzhou, 78 Jiuhua Boulevard North, Quzhou 324000, China.
Inorg Chem. 2021 Jun 21;60(12):8754-8764. doi: 10.1021/acs.inorgchem.1c00715. Epub 2021 Jun 2.
N,O-hybrid diamide ligands with N-heterocyclic skeletons are one of the promising extractants for the selective separation of actinides over lanthanides in a highly acidic HNO solution. In this work, three hard-soft donor mixed diamide ligands, pyridine-2,6-diylbis(pyrrolidin-1-ylmethanone) (Pyr-PyDA), 2,2'-bipyridine-6,6'-diylbis(pyr-rolidine-1-ylmethanone) (Pyr-BPyDA), and (1,10-phenanthroline-2,9-diyl)bis(pyrrolidin-1-ylmethanone) (Pyr-DAPhen), were synthesized and used to probe the influence of N-heterocyclic cores on the complexation and extraction behaviors with trivalent lanthanides and actinides. H NMR titration experiments demonstrated that 1:1 metal-to-ligand complexes were mainly formed between the three ligands and lanthanides, but 1:2 type complexes were also formed between tridentate Pyr-PyDA and Lu(III). The stability constants (log β) of these three ligands with two typical lanthanides, Nd(III) and Eu(III), were determined through spectrophotometric titration. It is found that Pyr-DAPhen formed the most stable complexes, while Pyr-PyDA formed the most unstable complexes with lanthanides, which coincided well with the following solvent extraction results. The solid-state structures of 1:1 type complexes of these three ligands with La(III), Nd(III), and Er(III) in nitrate media were identified by a single-crystal X-ray diffraction technique. Nd(III) and Er(III) were 10-coordinated with Pyr-PyDA, Pyr-BPyDA, and Pyr-DAPhen via one ligand molecule and three nitrate ions. La(III), because of its larger ionic radius, was 11-coordinated with Pyr-DAPhen through one ligand molecule, three nitrate ions, and one methanol molecule. Solvent extraction experiments showed that the preorganized phenanthroline-derived Pyr-DAPhen had the best extraction performance for trivalent actinide among the three ligands tested. This work provides some experimental insights into the design of more efficient ligands for trivalent actinide separation by adjusting the N-heterocyclic cores.
具有N-杂环骨架的N,O-混合二酰胺配体是在高酸性硝酸溶液中选择性分离锕系元素和镧系元素的有前景的萃取剂之一。在这项工作中，合成了三种硬-软供体混合二酰胺配体，吡啶-2,6-二基双（吡咯烷-1-基甲酮）（Pyr-PyDA）、2,2'-联吡啶-6,6'-二基双（吡咯烷-1-基甲酮）（Pyr-BPyDA）和（1,10-菲咯啉-2,9-二基）双（吡咯烷-1-基甲酮）（Pyr-DAPhen），并用于探究N-杂环核心对与三价镧系元素和锕系元素的络合及萃取行为的影响。1H NMR滴定实验表明，这三种配体与镧系元素主要形成1:1的金属-配体络合物，但三齿的Pyr-PyDA与Lu(III)也形成1:2型络合物。通过分光光度滴定法测定了这三种配体与两种典型镧系元素Nd(III)和Eu(III)的稳定常数（logβ）。发现Pyr-DAPhen与镧系元素形成的络合物最稳定，而Pyr-PyDA形成的络合物最不稳定，这与以下溶剂萃取结果非常吻合。通过单晶X射线衍射技术确定了这三种配体与La(III)、Nd(III)和Er(III)在硝酸盐介质中的1:1型络合物的固态结构。Nd(III)和Er(III)通过一个配体分子和三个硝酸根离子与Pyr-PyDA、Pyr-BPyDA和Pyr-DAPhen形成10配位。La(III)由于其较大的离子半径，通过一个配体分子、三个硝酸根离子和一个甲醇分子与Pyr-DAPhen形成11配位。溶剂萃取实验表明，在所测试的三种配体中，预组织的菲咯啉衍生的Pyr-DAPhen对三价锕系元素具有最佳的萃取性能。这项工作通过调整N-杂环核心，为设计更高效的用于分离三价锕系元素的配体提供了一些实验见解。
