Dainese Tiziano, Antonello Sabrina, Bogialli Sara, Fei Wenwen, Venzo Alfonso, Maran Flavio
Department of Chemistry , University of Connecticut , 55 North Eagleville Road , Storrs , Connecticut 06269 , United States.
ACS Nano. 2018 Jul 24;12(7):7057-7066. doi: 10.1021/acsnano.8b02780. Epub 2018 Jul 6.
The study of the molecular cluster Au(SR) has provided a wealth of fundamental insights into the properties of clusters protected by thiolated ligands (SR). This is also because this cluster has been particularly stable under a number of experimental conditions. Very unexpectedly, we found that paramagnetic Au(SR) undergoes a spontaneous bimolecular fusion to form another benchmark gold nanocluster, Au(SR). We tested this reaction with a series of Au clusters. The fusion was confirmed and characterized by UV-vis absorption spectroscopy, ESI mass spectrometry, H and C NMR spectroscopy, and electrochemistry. NMR evidences the presence of four types of ligand and, for the same proton type, double signals caused by the diastereotopicity arising from the chirality of the capping shell. This effect propagates up to the third carbon atom along the ligand chain. Electrochemistry provides a particularly convenient way to study the evolution process and determine the fusion rate constant, which decreases as the ligand length increases. No reaction is observed for the anionic clusters, whereas the radical nature of Au(SR) appears to play an important role. This transformation of a stable cluster into a larger stable cluster without addition of any co-reagent also features the bottom-up assembly of the Au building block in solution. This very unexpected result could modify our view of the relative stability of molecular gold nanoclusters.
对分子簇Au(SR)的研究为硫醇化配体(SR)保护的簇的性质提供了丰富的基本见解。这也是因为该簇在许多实验条件下都特别稳定。非常出乎意料的是，我们发现顺磁性的Au(SR)会发生自发的双分子融合，形成另一种基准金纳米簇Au(SR)。我们用一系列的金簇测试了这个反应。通过紫外可见吸收光谱、电喷雾电离质谱、氢核磁共振光谱和碳核磁共振光谱以及电化学对融合进行了确认和表征。核磁共振证明存在四种类型的配体，并且对于相同的质子类型，由于封端壳的手性产生的非对映异位性导致出现双重信号。这种效应沿着配体链传播到第三个碳原子。电化学提供了一种特别方便的方法来研究演化过程并确定融合速率常数，该常数随着配体长度的增加而降低。对于阴离子簇没有观察到反应，而Au(SR)的自由基性质似乎起着重要作用。这种在不添加任何共试剂的情况下将一个稳定簇转化为更大稳定簇的过程，也体现了溶液中Au结构单元的自下而上组装。这个非常出乎意料的结果可能会改变我们对分子金纳米簇相对稳定性的看法。
