4 research outputs found
Neat and Complete: Thiolate-Ligand Exchange on a Silver Molecular Nanoparticle
Atomically precise thiolate-protected
noble metal molecular nanoparticles
are a promising class of model nanomaterials for catalysis, optoelectronics,
and the bottom-up assembly of true molecular crystals. However, these
applications have not fully materialized due to a lack of ligand exchange
strategies that add functionality, but preserve the properties of
these remarkable particles. Here we present a method for the rapid
(<30 s) and complete thiolate-for-thiolate exchange of the highly
sought after silver molecular nanoparticle [Ag<sub>44</sub>(SR)<sub>30</sub>]<sup>−4</sup>. Only by using this method were we
able to preserve the precise nature of the particles and simultaneously
replace the native ligands with ligands containing a variety of functional
groups. Crucially, as a result of our method we were able to process
the particles into smooth thin films, paving the way for their integration
into solution-processed devices
Ag<sub>29</sub>(BDT)<sub>12</sub>(TPP)<sub>4</sub>: A Tetravalent Nanocluster
The bottom-up assembly
of nanoparticles into diverse ordered solids
is a challenge because it requires nanoparticles, which are often
quasi-spherical, to have interaction anisotropy akin to atoms and
molecules. Typically, anisotropy has been introduced by changing the
shape of the inorganic nanoparticle core. Here, we present the design,
self-assembly, optical properties, and total structural determination
of Ag<sub>29</sub>(BDT)<sub>12</sub>(TPP)<sub>4</sub>, an atomically
precise tetravalent nanocluster (NC) (BDT, 1,3-benzenedithiol; TPP,
triphenylphosphine). It features four unique tetrahedrally symmetrical
binding surface sites facilitated by the supramolecular assembly of
12 BDT (wide footprint bidentate thiols) in the ligand shell. When
each of these sites was selectively functionalized by a single phosphine
ligand, particle stability, synthetic yield, and the propensity to
self-assemble into macroscopic crystals increased. The solid crystallized
NCs have a substantially narrowed optical band gap compared to that
of the solution state, suggesting strong interparticle electronic
coupling occurs in the solid state
Reversible Size Control of Silver Nanoclusters via Ligand-Exchange
The properties of
atomically monodisperse noble metal nanoclusters
(NCs) are intricately intertwined with their precise molecular formula.
The vast majority of size-specific NC syntheses start from the reduction
of the metal salt and thiol ligand mixture. Only in gold was it recently
shown that ligand-exchange could induce the growth of NCs from one
atomically precise species to another, a process of yet unknown reversibility.
Here, we present a process for the ligand-exchange-induced growth
of atomically precise silver NCs, in a biphasic liquid–liquid
system, which is particularly of interest because of its complete
reversibility and ability to occur at room temperature. We explore
this phenomenon in-depth using Ag<sub>35</sub>(SG)<sub>18</sub> [SG
= glutathionate] and Ag<sub>44</sub>(4-FTP)<sub>30</sub> [4-FTP =
4-fluorothiophenol] as model systems. We show that the ligand-exchange
conversion of Ag<sub>35</sub>(SG)<sub>18</sub> into Ag<sub>44</sub>(4-FTP)<sub>30</sub> is rapid (<5 min) and direct, while the reverse
process proceeds slowly through intermediate cluster sizes. We adapt
a recently developed theory of reverse Ostwald ripening to model the
NCs’ interconvertibility. The model’s predictions are
in good agreement with the experimental observations, and they highlight
the importance of small changes in the ligand–metal binding
energy in determining the final equilibrium NC size. On the basis
of the insight provided by this model, we demonstrated experimentally
that by varying the choice of ligands, ligand-exchange can be used
to obtain different sized NCs. The findings in this work establish
ligand-exchange as a versatile tool for tuning cluster sizes
pH-Induced Surface Modification of Atomically Precise Silver Nanoclusters: An Approach for Tunable Optical and Electronic Properties
Noble metal nanoclusters
(NCs) play a pivotal role in bridging the gap between molecules and
quantum dots. Fundamental understanding of the evolution of the structural,
optical, and electronic properties of these materials in various environments
is of paramount importance for many applications. Using state-of-the-art
spectroscopy, we provide the first decisive experimental evidence
that the structural, electronic, and optical properties of Ag<sub>44</sub>(MNBA)<sub>30</sub> NCs can now be tailored by controlling
the chemical environment. Infrared and photoelectron spectroscopies
clearly indicate that there is a dimerization between two adjacent
ligands capping the NCs that takes place upon lowering the pH from
13 to 7