Matveev Petr I, Huang Pin-Wen, Kirsanova Anna A, Ananyev Ivan V, Sumyanova Tsagana B, Kharcheva Anastasia V, Khvorostinin Evgenii Yu, Petrov Vladimir G, Shi Wei-Qun, Kalmykov Stepan N, Borisova Nataliya E
Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory 1, Building 3, Moscow 119991, Russian Federation.
Laboratory of Nuclear Energy Chemistry, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China.
Inorg Chem. 2021 Oct 4;60(19):14563-14581. doi: 10.1021/acs.inorgchem.1c01432. Epub 2021 Sep 21.
Hybrid donor extractants are a promising class of compounds for the separation of trivalent actinides and lanthanides. Here, we investigated a series of sterically loaded diphosphonate ligands based on bipyridine (BiPy-PO-iPr and BiPy-PO-cHex) and phenanthroline (Phen-PO-iPr and Phen-PO-cHex). We studied their complex formation with nitrates of trivalent f-elements in solvent extraction systems (Am and Eu) and homogeneous acetonitrile solutions (Nd, Eu, and Lu). Phenanthroline extractants demonstrated the highest efficiency and selectivity [(Am/Eu) up to 14] toward Am(III) extraction from nitric acid solutions among all of the studied diphosphonates of N-heterocycles. The binding constants established by UV-vis titration also indicated stronger binding of sterically impaired diphosphonates compared to the primary substituted diphosphonates. NMR titration and slope analysis during solvent extraction showed the formation of 2:1 complexes at high concentrations (>10 mol/L) for phenanthroline-based ligands. According to UV-vis titrations at low concentrations (10-10 mol/L), the phenanthroline-based ligands formed 1:1 complexes. Bipyridine-based ligands formed 1:1 complexes regardless of the ligand concentration. Luminescence titrations revealed that the quantum yields of the complexes with Eu(III) were 81 ± 8% (BiPy-PO-iPr) and 93 ± 9% (Phen-PO-iPr). Single crystals of the structures [Lu(μ,κ-(iPrO)P(O)Phen(O)(OiPr))(NO)] and Eu(Phen-PO-iPr)(NO) were obtained by chemical synthesis with the Phen-PO-iPr ligand. X-ray diffraction studies revealed a closer contact of the -element with the aromatic N atoms in the case of sterically loaded P═O ligands compared with sterically deficient ligands. Density functional theory calculations allowed us to rationalize the observed selectivity trends in terms of the bond length, Mayer bond order, and preorganization energy.
混合供体萃取剂是用于分离三价锕系元素和镧系元素的一类很有前景的化合物。在此，我们研究了一系列基于联吡啶（BiPy-PO-iPr和BiPy-PO-cHex）和菲咯啉（Phen-PO-iPr和Phen-PO-cHex）的空间位阻二膦酸酯配体。我们在溶剂萃取体系（镅和铕）以及均相乙腈溶液（钕、铕和镥）中研究了它们与三价f元素硝酸盐的络合物形成情况。在所有研究的N-杂环二膦酸酯中，菲咯啉萃取剂对从硝酸溶液中萃取镅(III)表现出最高的效率和选择性[（镅/铕）高达14]。紫外-可见滴定法确定的结合常数也表明，与一级取代二膦酸酯相比，空间位阻二膦酸酯的结合更强。溶剂萃取过程中的核磁共振滴定和斜率分析表明，对于基于菲咯啉的配体，在高浓度（>10 mol/L）下形成2:1络合物。根据低浓度（10⁻¹⁰ mol/L）下的紫外-可见滴定，基于菲咯啉的配体形成1:1络合物。基于联吡啶的配体无论配体浓度如何都形成1:1络合物。发光滴定表明，与铕(III)形成的络合物的量子产率分别为81±8%（BiPy-PO-iPr）和93±9%（Phen-PO-iPr）。通过与Phen-PO-iPr配体进行化学合成，得到了结构[Lu(μ,κ-(iPrO)P(O)Phen(O)(OiPr))(NO)]和Eu(Phen-PO-iPr)(NO) 的单晶。X射线衍射研究表明，与空间位阻不足的配体相比，空间位阻的P═O配体情况下，f元素与芳香族N原子的接触更紧密。密度泛函理论计算使我们能够根据键长、迈耶键级和预组织能来解释观察到的选择性趋势。
