New Insights into the Bonding Properties of [Ag25(SR)18]−Nanoclusters from X-ray Absorption Spectroscopy

Atomically precise metal nanoclusters have attracted significant interest due to their molecule-like properties. [Ag25(SR)18]−is one of the Ag nanoclusters having a unique structure similar to its Au counterpart but different from most other Ag nanoclusters. In this study, a new five-shell fitting method was developed to analyze the extended X-ray absorption fine structure (EXAFS) spectra of [Ag25(SR)18]−to provide more insights into its bonding properties. This new method was successfully applied to compare the bond lengths as the temperature changed from 300 to 90 K. Interestingly, the metal core of [Ag25(SR)18]−showed negative thermal expansion behavior that was not observed for Au25(SR)18. These unique bonding properties of [Ag25(SR)18]−could be related to the Ag4tetrahedral units found in the metal core, which were absent in Au25(SR)18. These new findings about its bonding properties can provide a better understanding of the structure–property relationship of [Ag25(SR)18]−. This new EXAFS analysis method could be applied to gain insights into the bonding properties of other metal nanoclusters.