Solvent-Induced Reverse-Ostwald Ripening: Structure Conversion from Ag56 to Ag45 Clusters and Its Impact on Catalytic Reduction of 4-Nitrophenol.

Controlled structure transformation in metal clusters is crucial for accessing novel architectures and understanding their structure-property correlations. Herein, we report a solvent-induced reverse-Ostwald ripening process between two atomically precise silver clusters, Ag56 and Ag45, which exhibit solvent-dependent structure variation: Ag56 remains stable in dichloromethane, whereas exposure to pentane induces conversion to Ag45. The compositions and structures of both clusters were determined by electrospray ionization mass spectrometry (ESI-MS) and single-crystal X-ray diffraction (SXRD). Structure analysis indicates that the Ag45 forms via fragmentation and reorganization of the Ag56 framework, distinct from the conventional Ostwald ripening observed in larger nano-systems. Although Ag45 and Ag56 share certain structural similarities, Ag45 exhibits superior stability and higher catalytic activity for the reduction of 4-nitrophenol (4-NP) than Ag56. Density functional theory (DFT) calculations further elucidate the catalytic reduction pathway on Ag45. This work demonstrates a solvent-mediated reverse-Ostwald ripening pathway in silver clusters, providing atomic-level insights into active site construction and offering a blueprint for designing robust, cluster-based catalysts.