Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States.
J Am Chem Soc. 2020 Aug 5;142(31):13500-13506. doi: 10.1021/jacs.0c05217. Epub 2020 Jul 22.
Lanthanides (Ln) are critical materials used for many important applications, often in the form of coordination compounds. Tuning the thermodynamic stability of these compounds is a general concern, which is not readily achieved due to the similar coordination chemistry of lanthanides. Herein, we report two 18-membered macrocyclic ligands called macrodipa and macrotripa that show for the first time a dual selectivity toward both the light, large Ln ions and the heavy, small Ln ions, as determined by potentiometric titrations. The lanthanide complexes of these ligands were investigated by NMR spectroscopy and X-ray crystallography, which revealed the occurrence of a significant conformational toggle between a 10-coordinate Conformation A and an 8-coordinate Conformation B that accommodates Ln ions of different sizes. The origin of this selectivity pattern was further supported by density functional theory (DFT) calculations, which show the complementary effects of ligand strain energy and metal-ligand binding energy that contribute to this conformational switch. This work demonstrates how novel ligand design strategies can be applied to tune the selectivity pattern for the Ln ions.
镧系元素（Ln）是许多重要应用中关键的材料，通常以配位化合物的形式存在。由于镧系元素的配位化学相似，因此调节这些化合物的热力学稳定性是一个普遍关注的问题，而这并不容易实现。在此，我们报告了两种 18 元大环配体，分别称为 macrodipa 和 macrotripa，它们首次表现出对轻、大镧系元素离子和重、小镧系元素离子的双重选择性，这是通过电位滴定法确定的。通过 NMR 光谱和 X 射线晶体学研究了这些配体的镧系元素配合物，结果表明存在从 10 配位的 Conformation A 到 8 配位的 Conformation B 的显著构象翻转，这种构象翻转可容纳不同大小的镧系元素离子。这种选择性模式的起源进一步得到了密度泛函理论（DFT）计算的支持，该计算表明配体应变能和金属-配体结合能的互补效应对这种构象转变有贡献。这项工作展示了如何应用新的配体设计策略来调节镧系元素离子的选择性模式。
