The simple diamide ligand L was previously shown to selectively precipitate gold from acidic solutions typical of e-waste leach streams, with precipitation of gallium, iron, tin, and platinum possible under more forcing conditions. Herein, we report direct competition experiments to afford the order of selectivity. Thermal analysis indicates that the gold-, gallium-, and iron-containing precipitates present as the most thermodynamically stable structures at room temperature, while the tin-containing structure does not. Computational modeling established that the precipitation process is thermodynamically driven, with ion exchange calculations matching the observed experimental selectivity ordering. Calculations also show that the stretched ligand conformation seen in the X-ray crystal structure of the gold-containing precipitate is more strained than in the structures of the other metal precipitates, indicating that intermolecular interactions likely dictate the selectivity ordering. This was confirmed through a combination of Hirshfeld, noncovalent interaction (NCI), and quantum theory of atoms in molecules (QTAIM) analyses, which highlight favorable halogen···halogen contacts between metalates and pseudo-anagostic C–H···metal interactions in the crystal structure of the gold-containing precipitate.

中文翻译：

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热力学控制驱动的叔二酰胺选择性金沉淀


简单的二酰胺配体 L 先前已被证明可以从电子废物浸出流中典型的酸性溶液中选择性沉淀金，并且在更强的条件下可能沉淀镓、铁、锡和铂。在这里，我们报告直接竞争实验以提供选择性顺序。热分析表明，含金、镓和铁的沉淀物在室温下表现为热力学最稳定的结构，而含锡结构则不然。计算模型确定沉淀过程是热力学驱动的，离子交换计算与观察到的实验选择性排序相匹配。计算还表明，在含金沉淀物的 X 射线晶体结构中看到的拉伸配体构象比其他金属沉淀物的结构中的应变更大，这表明分子间相互作用可能决定了选择性排序。通过结合赫什菲尔德、非共价相互作用 (NCI) 和分子中原子量子理论 (QTAIM) 分析证实了这一点，该分析强调了金属盐之间有利的卤素·卤素接触和伪抑制 C–H·金属相互作用含金沉淀物的晶体结构。