Interactions between Ultrastable Na₄Ag₄₄(SR)₃₀ Nanoclusters and Coordinating Solvents: Uncovering the Atomic-Scale...

Recently, silver nanoclusters have garnered considerable attention after the high-yield synthesis and crystallization of a thiolate-protected silver nanocluster, Na₄Ag₄₄(SR)₃₀ (SR, protecting thiolate ligand). One intriguing feature of Na₄Ag₄₄(SR)₃₀ is its outstanding stability and resistance to chemical reactions, in striking difference from other silver nanostructures whose susceptibility to oxidation (tarnishing) has been commonly observed and thus limits their applications in nanotechnology. Herein, we report the mechanism on the ultrahigh stability of Na₄Ag₄₄(SR)₃₀ by uncovering how coordinating solvents interact with the Na₄Ag₄₄(SR)₃₀ nanocluster at the atomic scale. Through synchrotron X-ray experiments and theoretical calculations, it was found that strongly coordinating aprotic solvents interact with surface Ag atoms, particularly between ligand bundles, which compresses the Ag core and relaxes surface metal-ligand interactions. Furthermore, water was used as a cosolvent to demonstrate that semiaqueous conditions play an important role in protecting exposed surface regions and can further influence the local structure of the silver nanocluster itself. Notably, under semiaqueous conditions, aprotic coordinating solvent molecules preferentially remain on the metal surface while water molecules interact with ligands, and ligand bundling persisted across the varied solvation conditions. This work offers an atomic level mechanism on the ultrahigh stability of the Na₄Ag₄₄(SR)₃₀ nanoclusters from the nanocluster-coordinating solvent interaction perspective, and implies that nanocluster-solvent interactions should be carefully considered moving forward for silver nanoclusters, as they can influence the electronic/chemical properties of the nanocluster as well as the surface accessibility of small molecules for potential catalytic and biomedical applications.