Synthesis and characterization of mixed ligand chiral nanoclusters

Chiral mixed ligand silver nanoclusters were synthesized in the presence of a chiral and an achiral ligand. The ratio of the ligands was changed to track the formation of these clusters. While the chiral ligand lead to nanoparticles, Presence of the achiral ligand induced the formation of nanoclusters with chiral properties

Model for the Phase Transfer of Nanoparticles Using Ionic Surfactants

Ionic surfactants are widely used for the phase transfer of nanoparticles from aqueous to organic phases; however, a model that can be used to select ionic surfactants based on the nanoparticle solution properties has yet to be established. Here, we have studied the phase transfer of a variety of nanoparticles and have identified hydrophobicity, steric repulsion, and interfacial tension as key factors in determining whether or not phase transfer will occur. Based on these studies, we have developed a simple model for phase transfer wherein the success of the surfactant depends only on three criteria. The phase transfer agents must (i) efficiently load onto or cross the interface, (ii) solubilize the nanoparticles in the receiving phase, and (iii) sterically stabilize the nanoparticles to prevent aggregation due to van der Waals forces between the inorganic cores. Using these criteria, the effectiveness of ionic surfactants could be predicted based on their molecular geometry and the properties of the nanoparticle solutions. These rules provide a basis for choosing surfactants for phase transfer of spherical nanoparticles up to 16 nm in diameter and advances the development of a general model of nanoparticle phase transfer, which would include all nanoparticle shapes, sizes, and solvents

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

[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