Molecular-like Transformation from PhSe-Protected Au₂₅ to Au₂₃ Nanocluster and Its Application

In this work, we report a new size conversion from [Au 25 (SePh) 18 ] − to [Au 23 (SePh) 16 ] − nanoclusters under the reductive condition (NaBH 4 ). This novel transformation induced by only reductant has not been reported before in the field of gold nanocluster. The conversion process is studied via MALDI mass spectrometry, and UV–vis spectroscopy. These results demonstrate that the [Au 23 (SePh) 16 ] − nanocluster is directly obtained by pulling out two units of “Au-SeR” from the [Au 25 (SePh) 18 ] − nanocluster, which is similar to the “small molecular” reaction. In order to further understand this novel conversion, DFT calculations were performed, in which, with addition of two H – in the [Au 25 (SeH) 18 ] − model, two Au atoms will depart from the structure of the [Au 25 (SeH) 18 ] −, which is consistent with the experimental results. Furthermore, the as-prepared [Au 23 (SePh) 16 ] − nanoclusters can be converted into [Au 25 (PET) 18 ] − nanocluster (PET = SCH 2 CH 2 Ph) with excess PET under the reductive condition, which is quite remarkable due to a stronger bond of Au–Se in comparison to Au–S of the final product. Interestingly, the number of the PET ligands on the surface of the 25-atoms nanocluster can be controlled by the addition of the reductant. Based on these results, a circularly progressive mechanism of ligand exchange is proposed. This may offer a new approach to synthesis of new gold nanoclusters and also have significant contribution for understanding and further exploration of the mechanism of ligand exchange.