As critical minerals such as Ni and Co are essential for modern technologies and clean energy solutions, there is an urgent need to develop sustainable extraction methods to meet rising demand and mitigate environmental impacts of existing mining practices. 2-Hydroxyaryloximes are promising candidates for metal separation as they form stable size-selective pseudomacrocyclic dimers through hydrogen-bonding networks. These ligands exhibit pH-dependent coordination properties, influenced by the protonation state of the phenolic oxygen. Herein, structure–property relationships of seven 2-hydroxyaryloximes and their efficacy as ligands in liquid–liquid extraction schemes for Ni and Co are explored to provide a framework for designing ligands that could lead to more effective and sustainable solvent extraction processes. A generalized multigram synthesis for 2-hydroxyaryloximes is reported along with concentration- and solvent-dependent characterization of the complexes. Steric and electronic effects induced by modifications of peripheral substituent groups on dimerization constants and pK_a values of the complexes were systematically investigated using NMR and potentiometric titrations. Our findings demonstrate the potential to tune the extractive properties of 2-hydroxyaryloximes, allowing for optimization of pH windows for selective metal recovery. Solvent extraction experiments with Ni and Co systems further illustrate that extraction efficiency and selectivity can be altered through rational ligand design.

中文翻译：

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2-羟基芳氧肚胺作为选择性第一行过渡金属液-液萃取的可调萃取剂：二聚化系数、pKa 和 pH0.5


由于镍和钴等关键矿物对于现代技术和清洁能源解决方案至关重要，因此迫切需要开发可持续的提取方法，以满足不断增长的需求并减轻现有采矿方式对环境的影响。2-羟基芳环酰亚胺是金属分离的有前途的候选者，因为它们通过氢键网络形成稳定的尺寸选择性伪大环二聚体。这些配体表现出 pH 依赖性配位特性，受酚氧质子化状态的影响。在本文中，探讨了七种 2-羟基芳氧醚的结构-性质关系及其在 Ni 和 Co 的液-液萃取方案中作为配体的功效，为设计配体提供了一个框架，从而可以导致更有效和可持续的溶剂萃取过程。报道了 2-羟基芳氧醚的广义多克合成以及复合物的浓度和溶剂依赖性表征。使用 NMR 和电位滴定系统研究了外周取代基修饰对复合物二聚化常数和 pK_a 值的空间和电子效应。我们的研究结果表明，有可能调节 2-羟基芳氧酰亚胺的提取特性，从而优化 pH 窗口以进行选择性金属回收。使用 Ni 和 Co 系统的溶剂萃取实验进一步表明，可以通过合理的配体设计来改变萃取效率和选择性。