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

Abstract

Silver nanoparticles with an atomically precise molecular formula [Ag 25 (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., [Au 25 (SR) 18 ] − , in terms of number of metal atoms, ligand count, superatom electronic configuration, and atomic arrangement. Furthermore, both [Ag 25 (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.S ilver and gold have contrasting physical and chemical properties despite their similarity in atomic size, structure, and bulk-lattice. Throughout the ages, humankind was captivated by the properties of these lustrous metals. However, only in the last century or so have scientists been able to investigate the underlying fundamental differences between silver and gold and their origin down to the nanoscale. This pursuit was made possible through advancements in nanofabrication techniques, which enabled the synthesis of metal nanostructures and their confinement in organic shells. 1,2 These advancements accentuated the differences in chemical properties between gold and silver. For example, gold nanoparticles were found to be effective catalysts for several reactions such as carbon monoxide oxidation 3 and aldehydes reduction, 4 and their noble behavior makes them relatively biocompatible 5,6 and thus useful for biomedicine. 6,7 On the other hand, silver nanoparticles were found to exhibit much lower catalytic utility and are quite cytotoxic; hence, they are used often in antibacterial surface coatings. 1,8 The discovery of nanoclusters, which are atomically precise nanoparticles, has brought forth a nanoparticle system, whose properties are well-defined, modeled, and explained. 1,2,9−13 In the past 10 years, the nanocluster community has made great strides in the synthesis, isolation, and crystal structure determination of a remarkable number of gold species, 2,9,10 but only a few species of silver.

Structure-conserving spontaneous transformations between nanoparticles

“…The reason for choosing Au 25 (PET) 18 as the movable and flexible molecule was that PET ligands have a greater torsional flexibility than the DMBT ligands due to the longer chain length which would result in lower energy minima during the optimization over the greater number of torsional degrees of freedom. We have used the reported crystal structure coordinates2228 of Ag 25 (SR) 18 and Au 25 (SR) 18 , without any structural relaxation, as the input for the molecular docking study. Different types of atoms in the ligands DMBT and PET and the charges on them are given in Supplementary Fig.…”

“…28), manifest dramatic chemical reactivity. We use mass spectrometry to study these reactions in detail.…”

[Ag67(SPhMe2)32(PPh3)8]3+: Synthesis, Total Structure, and Optical Properties of a Large Box-Shaped Silver Nanocluster

“…Nevertheless, the number of stable atomically monodisperse thiolate-protected silver NCs is rising, having attracted much research attention with the hope of utilizing them as a viable and cheaper alternative to gold. [25][26][27][28][29][30][31][32][33][34] A key challenge remaining for silver NCs is obtaining highly anisotropic shapes. In gold, NCs of anisotropic shapes were reported through solely thiols 35,36 and co-ligands of phosphines and thiols 37,38 .…”

Switching a Nanocluster Core from Hollow to Nonhollow

“…The typical routes for metal NC synthesis are: i) direct reduction of metal precursors in the presence of desired ligands, [22][23][24][25][26][27][28] ii) postsynthetic ligand-exchange (LE), [29][30][31][32][33][34][35] and iii) metal-exchange 15,[36][37][38][39][40][41] . Among these methods, LE has recently been widely adopted for preparing novel gold NCs [42][43][44] .…”