Increasing the thermodynamic stability of metal complexes in water is a key challenge for various applications of coordination chemistry. In this study, a calix[6]arene macrocycle functionalized with three imidazole units on the narrow rim and three primary amino legs on the wide rim was synthesized and studied. This ligand coordinates a Zn2+ cation in water, within a pH window centered around 7, through the three imidazole units and one self-included amino leg occupying the coordination site within the macrocycle cavity. The coordination process benefits from a favourable entropic effect, conferring greater thermodynamic stability to the resulting ouroboros-like complex compared to the one stabilized by an exogenous amine. Additionally, the intramolecular coordination ensures a supramolecular protection, which can be exploited for the site-selective functionalization of two out of the three amino groups. These findings demonstrate that the use of macrocyclic ligands capable of forming ouroboros-like molecular complexes represent a valuable strategy for stabilizing metal ions in water.

中文翻译：

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开发基于水溶性衔尾蛇样 calix[6]芳烃-三咪唑的配体，以增强锌的结合


提高金属配合物在水中的热力学稳定性是配位化学各种应用的关键挑战。在这项研究中，合成并研究了一种 calix[6]芳烃大环，其功能化在窄边缘上具有三个咪唑单元，在宽边缘上具有三个伯氨基腿。该配体在以 7 为中心的 pH 窗口内，通过三个咪唑单元和一个占据大环腔内配位位点的自包含氨基腿，在以 7 为中心的 pH 窗口内，将水中的 Zn2+ 阳离子配位。配位过程受益于有利的熵效应，与由外源胺稳定的复合物相比，所得的衔尾蛇状复合物具有更高的热力学稳定性。此外，分子内配位确保了超分子保护，可用于三个氨基中两个氨基的位点选择性官能化。这些发现表明，使用能够形成衔尾蛇样分子复合物的大环配体代表了稳定水中金属离子的宝贵策略。