[Ag₂₅(SR)₁₈]⁻: The “Golden” Silver Nanoparticle

Silver nanoparticles with an atomically precise molecular formula [Ag₂₅(SR)₁₈]⁻ (−SR: thiolate) are synthesized, and their single-crystal structure is determined. This synthesized nanocluster is the only silver nanoparticle that has a virtually identical analogue in gold, i.e., [Au₂₅(SR)₁₈]⁻, in terms of number of metal atoms, ligand count, superatom electronic configuration, and atomic arrangement. Furthermore, both [Ag₂₅(SR)₁₈]⁻ and its gold analogue share a number of features in their optical absorption spectra. This unprecedented molecular analogue in silver to mimic gold offers the first model nanoparticle platform to investigate the centuries-old problem of understanding the fundamental differences between silver and gold in terms of nobility, catalytic activity, and optical property

Switching a Nanocluster Core from Hollow to Nonhollow

Modulating the structure–property relationship in atomically precise nanoclusters (NCs) is vital for developing novel NC materials and advancing their applications. While promising biphasic ligand-exchange (LE) strategies have been developed primarily to attain novel NCs, understanding the mechanistic aspects involved in tuning the core and the ligand-shell of NCs in such biphasic processes is challenging. Here, we design a single phase LE process that enabled us to elucidate the mechanism of how a hollow NC (e.g., [Ag₄₄(SR)₃₀]^4–, SR: thiolate) converts into a nonhollow NC (e.g., [Ag₂₅(SR)₁₈]⁻) and vice versa. Our study reveals that the complete LE of the hollow [Ag₄₄(SPhF)₃₀]^4– NCs (SPhF: 4-fluorobenzenethiolate) with incoming 2,4-dimethylbenzenethiol (HSPhMe₂) induced distortions in the Ag₄₄ structure forming the nonhollow [Ag₂₅(SPhMe₂)₁₈]⁻ by a disproportionation mechanism, while the reverse reaction of [Ag₂₅(SPhMe₂)₁₈]⁻ with HSPhF prompted an unusual dimerization of Ag₂₅, followed by a rearrangement step that reproduces the original [Ag₄₄(SPhF)₃₀]^4–. Remarkably, both the forward and the backward reactions proceed through similar size intermediates that seem to be governed by the boundary conditions set by the thermodynamic and electronic stability of the hollow and nonhollow metal cores. Furthermore, the resizing of NCs highlights the surprisingly long-range effect of the ligands which are felt by atoms far deep in the metal core, thus opening a new path for controlling the structural evolution of nanoparticles