Atomically Precise Silver Nanoclusters: Controlled Synthesis and Assembly into Structurally Diverse Frameworks with Tailored Optical Properties

Abstract

Ligand-protected metal nanoclusters (NCs), which are ultra-small nanoparticles marked by their atomic precision, are distinctly importance for contemporary nanomaterials. NCs have attracted significant research attention for utilizing their novel optical and physicochemical properties in various applications, including fluorescence sensing, catalysis, and biomedical applications. This dissertation deals with ligand-protected atomically precise silver NCs and is divided into two main parts. The first part is focused on the exploration and design of well-defined silver NCs through surface co-ligand engineering. The second part is related to the development of silver NC-based frameworks (NCFs).

In the first part, we designed a synthetic strategy based on engineering the structure of the phosphine co-ligands with thiols to generate the large box-shaped [Ag67(SPhMe2)32(PPh3)8]3+ (referred to as Ag67) NC. The strategy demonstrates that the combined use of judiciously chosen thiol and phosphine co-ligands can result in stable highly anisotropic box-like shapes. The optical absorption spectrum of the Ag67 NC displays highly structured multiple sharp peaks. The crystal structure shows a Ag23 core formed of a centered cuboctahedron (an unprecedented core geometry in silver clusters), which is encased by a layer with a composition of Ag44S32P8 arranged in the shape of a box. The electronic structure of this box-shaped cluster resembles a jellium box model with 32 free electrons.

In the second part, a novel approach is developed for the assembly and linkage of atomically precise Ag NCs into one-dimensional (1D) and two-dimensional (2D) NC-based frameworks (NCFs) with atomic-level control over cluster size and dimensionality. With this approach three novel, but related, crystal structures (one silver NC and two NCFs) were synthesized. These structures have the same protecting ligands, and also the same organic linker. The three structures exhibit a similar square gyrobicupola geometry of the building NC unit with only a single Ag atom difference. The critical role of using a chloride template in controlling the NC’s nuclearity was demonstrated, as well as the effect of a single Ag atom difference in the NC’s size on the NCF’s dimensionality, optical properties, and thermal stability.