Smock Sara R, Alimento Ryan, Mallikarjun Sharada Shaama, Brutchey Richard L
Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States.
Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089, United States.
Inorg Chem. 2021 Sep 6;60(17):13699-13706. doi: 10.1021/acs.inorgchem.1c02018. Epub 2021 Aug 15.
N-Heterocyclic carbenes (NHCs) are versatile L-type ligands that have been shown to stabilize coinage metal chalcogenide nanocrystals, such as AgS, remarkably well. However, very little research has been done on the interaction between NHC ligands and coinage metal chalcogenide nanocrystal surfaces and subsequent ligand exchange reactions. Herein, solution H nuclear magnetic resonance methods were used to monitor ligand exchange reactions on stoichiometric AgS nanocrystal platforms with various primary amine and carboxylic acid ligands. Despite the introduction of new ligands, the native NHC ligands remain tightly bound to the AgS nanocrystal surface and are not displaced at room temperature. Primary amine and carboxylic acid ligands demonstrated quantitative ligand exchange only after the samples had been heated with an excess incoming ligand, which implies a strong NHC-Ag binding energy. Density functional theory affirms that a model NHC ligand binds the strongest to a AgS cluster surface, followed by amine and carboxylic acid binding; computational analysis is therefore in line with the absence of NHC displacement observed in experiments. Both the bulky sterics of the C14-alkyl chains on the NHC and the high energies for the binding of NHC to the AgS surface contribute to the superior colloidal stability over conventional long-chain amine or carboxylic acid ligands (many months vs hours to days).
N-杂环卡宾（NHCs）是用途广泛的L型配体，已被证明能非常有效地稳定货币金属硫族化物纳米晶体，如硫化银。然而，关于NHC配体与货币金属硫族化物纳米晶体表面之间的相互作用以及随后的配体交换反应，所做的研究非常少。在此，采用溶液氢核磁共振方法监测化学计量比的硫化银纳米晶体平台上与各种伯胺和羧酸配体的配体交换反应。尽管引入了新的配体，但天然的NHC配体仍紧密结合在硫化银纳米晶体表面，在室温下不会被取代。伯胺和羧酸配体只有在样品与过量的引入配体一起加热后才表现出定量的配体交换，这意味着NHC与银之间有很强的结合能。密度泛函理论证实，一个模型NHC配体与硫化银簇表面的结合最强，其次是胺和羧酸的结合；因此，计算分析与实验中观察到的NHC未被取代的情况一致。NHC上C14烷基链的庞大空间位阻以及NHC与硫化银表面结合的高能量，共同导致了其比传统长链胺或羧酸配体具有更优异的胶体稳定性（数月而非数小时至数天）。
