Abstract Diglycolamides (DGAs) show excellent application prospects for the extraction and separation of rare earth metals from highly radioactive liquid wastes and rare earth ores. The extraction ability of DGAs for rare earth ions in nitrate or chloride media increases with increasing atomic number of the rare earth metal. To understand the origin of this phenomenon, three binuclear crystals [Ln(TEDGA)3][Ln(NO3)6] of N,N,N′,N′-tetraethyldiglycolamide (TEDGA) with rare earth ions La(III), Pr(III) and Eu(III) were prepared and characterized crystallographically. The three complexes belong to the triclinic crystal system, P-1 space group. The bond lengths of Ln–Oamide are significantly shorter than those of Ln–Oether in the same crystal. The Ln–Oamide and Ln–Oether bond lengths gradually decrease with increasing atomic number of the rare earth ion. The dihedral angle formed by TEDGA and metal ions through the tridentate coordination gradually increases with increasing metal ion atomic number, tending toward the formation of sizeable planar coordination structures for the most massive rare earth ions. The structures of the compounds formed by the extractant and metal ion were optimized by means of DFT simulations. We found that the interaction between TEDGA and the rare earth ion is dominated by electrostatic interaction by analyzing binding energy, WBIs, Mulliken charge, natural electron configurations, and molecular orbital interaction. The covalent component of the Ln–O bonds of the complexes increases with increasing metal atomic number. The observed increase in extraction and separation capacity of diglycolamides for rare earth ions with increasing atomic number might be due to the formation of two five-member rings by one tridentate ligand. The rare earth ions with large atomic numbers tend to form planar structures with large dihedral angles with DGA ligands.

中文翻译：

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从晶体结构和 DFT 模拟中对二甘醇酰胺萃取和分离稀土的理论阐明

摘要 二甘醇酰胺（DGAs）在从高放射性废液和稀土矿石中提取和分离稀土金属方面具有良好的应用前景。DGA 对硝酸盐或氯化物介质中稀土离子的萃取能力随着稀土金属原子序数的增加而增加。为了理解这种现象的起源，N,N,N',N'-四乙基二甘醇酰胺 (TEDGA) 的三个双核晶体 [Ln(TEDGA)3][Ln(NO3)6] 与稀土离子 La(III), Pr (III) 和 Eu(III) 的制备和晶体学表征。这三种配合物属于三斜晶系，P-1空间群。在同一晶体中，Ln-Oamide 的键长明显短于 Ln-Oether 的键长。Ln-Oamide 和 Ln-Oether 键长随着稀土离子原子序数的增加而逐渐减小。TEDGA 与金属离子通过三齿配位形成的二面角随着金属离子原子序数的增加而逐渐增大，趋向于为最大质量的稀土离子形成相当大的平面配位结构。通过DFT模拟优化了萃取剂和金属离子形成的化合物的结构。通过分析结合能、WBI、Mulliken电荷、自然电子构型和分子轨道相互作用，我们发现TEDGA与稀土离子之间的相互作用以静电相互作用为主。配合物的 Ln-O 键的共价成分随着金属原子序数的增加而增加。随着原子序数的增加，观察到的二甘醇酰胺对稀土离子的萃取和分离能力的增加可能是由于一个三齿配体形成了两个五元环。具有大原子序数的稀土离子倾向于与 DGA 配体形成具有大二面角的平面结构。