Ligand and Metal Exchanges between [(AuAg)44(SR)30]4- Clusters via Bimolecular Superatomic Collision
Hai-Feng Su1, Hongwen Deng1, Lan-Sun Zheng1
1State Key Laboratory for Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China.
Abstract:
Reported herein is a study of intercluster exchanges of ligands and/or metals between [(AuAg)44(SR)30]4- nanoclusters via a combination of electrospray ionization mass spectrometry, X-ray crystallography, and UV-vis spectroscopy. The results revealed that ligand exchange reactions are instantaneous, giving rise to the standard Gaussian distribution indicative of a random exchange or substitution process. In sharp contrast, metal exchange reactions are slow (hours to days), resulting in fractal-like patterns. The intercluster Au-Ag exchange occurs in the innermost icosahedral core of the cluster. These reactions, when performed with a permeable membrane separating the two reactants, provided strong evidence that both exchanges require bimolecular collisions resembling conventional SN2-type reactions between two superatomic clusters. This notion was further corroborated by the unexpected observation of "half" Au and "half" Ag peaks in the mass spectra, which may be taken as circumstantial evidence for the formation of a transient dimer [(AuAg)44(SR)30]28- upon intercluster collisions in solution. Finally, the effects of experimental conditions, such as solvent and temperature, were also investigated.
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