Laboratoire des Matériaux Mésoscopiques et Nanométriques, UMR CNRS 7070, UPMC-Université Paris 6 , 4 place Jussieu, 75252 Paris, France.
Langmuir. 2013 Oct 15;29(41):12647-56. doi: 10.1021/la402407k. Epub 2013 Oct 1.
Synthesizing stable Au and Ag nanocrystals of narrow size distribution from metal-N-heterocyclic carbene (NHC) complexes remains a challenge, particularly in the case of Ag and when NHC ligands with no surfactant-like properties are used. The formation of nanocrystals by one-phase reduction of metal-NHCs (metal = Au, Ag) bearing common NHC ligands, namely 1,3-diethylbenzimidazol-2-ylidene (L(1)), 1,3-bis(mesityl)imidazol-2-ylidene (L(2)), and 1,3-bis(2,6-(i)Pr2C6H3)imidazol-2-ylidene (L(3)), is presented herein. We show that both Au and Ag nanocrystals displaying narrow size distribution can be formed by reduction with amine-boranes. The efficiency of the process and the average size and size distribution of the nanocrystals markedly depend on the nature of the metal and NHC ligand, on the sequence in the reactant addition (i.e., presence or absence of thiol during the reduction step), and on the presence or absence of oxygen. Dodecanethiol was introduced to produce stable nanocrystals associated with narrow size distributions. A specific reaction is observed with Ag-NHCs in the presence of thiols whereas Au-NHCs remain unchanged. Therefore, different organometallic species are involved in the reduction step to produce the seeds. This can be correlated to the lack of effect of NHCs on Ag nanocrystal size. In contrast, alteration of Au nanocrystal average size can be achieved with a NHC ligand of great steric bulk (L(3)). This demonstrates that a well-defined route for a given metal cannot be extended to another metal.
从金属-N-杂环卡宾（NHC）配合物合成具有窄尺寸分布的稳定金和银纳米晶体仍然是一个挑战，特别是在 Ag 的情况下，并且当使用没有类似表面活性剂性质的 NHC 配体时。本文报道了具有常见 NHC 配体，即 1,3-二乙基苯并咪唑-2-亚基（L(1)）、1,3-双（均三甲苯基）咪唑-2-亚基（L(2)）和 1,3-双（2,6-（i）Pr2C6H3）咪唑-2-亚基（L(3)）的金属-NHC（金属=Au、Ag）的单相还原形成纳米晶体。我们表明，通过胺硼烷还原可以形成具有窄尺寸分布的金和银纳米晶体。该过程的效率以及纳米晶体的平均尺寸和尺寸分布明显取决于金属和 NHC 配体的性质、反应物添加的顺序（即在还原步骤中是否存在硫醇）以及是否存在氧气。十二硫醇被引入以产生与窄尺寸分布相关的稳定纳米晶体。在存在硫醇的情况下观察到 Ag-NHC 的特定反应，而 Au-NHC 保持不变。因此，在还原步骤中涉及不同的有机金属物种来产生种子。这可以与 NHC 对 Ag 纳米晶体尺寸没有影响相关联。相比之下，可以通过具有大空间位阻的 NHC 配体（L(3)）来改变 Au 纳米晶体的平均尺寸。这表明对于给定的金属，不能将明确的途径扩展到另一种金属。
