|Tuesday, July 19|
Synthesis of gold nanoparticles and their self-assembly into two-dimensional superlattices
* Chiara Moretti, CNRS, France
Claire Goldmann, CNRS, France
Marianne Impéror-Clerc , CNRS, France
Benjamin Abécassis, CNRS, France
Nanoparticles (NPs) can spontaneously assemble into a large variety of superlattices going from amorphous glassy assemblies towards crystalline phases and even more complex structures. The aim of our research is to control the final assembled structure to have a predictive approach towards NP superlattices design. Gold NPs serve as a unique model system due to the broad range of syntheses available, their straightforward functionalization via thiol chemistry and their unique plasmonic and optical properties. We first have synthesized well-defined hydrophobic spherical gold colloidal nanoparticles with a very low polydispersity using a novel seed-mediated synthesis strategy. Secondly, we have investigated their two-dimensional self-assembly at the liquid/air interface from the evaporation of a dispersion of spherical Au NPs on a liquid surface. Many different structures were observed: hexagonal close-packed monolayers, Moiré patterns, bilayers and multilayers, fused NPs, binary NP superlattices, and also more complex structures, such as Frank-Kasper phases. Our study helps to establish a robust and reproducible protocol for film formation and it is a first step to obtain more complex superlattices, including binary structures or by using other kind of shapes to design new nanomaterials.
Synthesis of Mesoionic Carbene (MIC) Stabilized Gold Nanoparticles from 1,2,3-Triazolium Salts
* Salem Ba Sowid , Sorbonne Université , France
Alexandre Porcheron, Sorbonne Université, France
Omar Sadek, Sorbonne Université, France
Dimitri Mercier, PSL Research University, France
Nathalie Bridonneau, Sorbonne Université, France
Laura Hippolyte, Sorbonne Université, France
Clément Chauvier, Sorbonne Université, France
Louis Fensterbank, Sorbonne Université, France
* François Ribot, Sorbonne Université, France
Mesoionic carbenes (MICs) are robust subclass of N-heterocyclic carbenes (NHCs), which are very efficient stabilizing ligands. Yet, unlike classical NHCs, MICs can be easily synthesized via simple click reaction. Herein, simple one-pot straightforward synthesis of MIC-stabilized gold nanoparticles directly from 1,2,3-triazolium salts and tetrachloroauric acid is reported. This highly stable AuNPs were characterised by TEM, UV-Vis, and XPS.
Construction of covalently crosslinked gold cluster networks based on ligand-mediated reactions
* Yuki Saito, Hokkaido university, Japan
Yukatsu Shichibu, Hokkaido university, Japan
Katsuaki Konishi, Hokkaido University, Japan
Atomically precise ligand-protected molecular gold clusters with defined chemical formula have attracted much attention because they exhibit unique optical and catalytic properties that are not found in simple gold complexes or nanoparticles. Recently, intense interests in the behaviors of clusters in condensed states have emerged in relation to the possible synergetic effects of multiple clusters in proximity that could lead to the appearance of distinct properties. The use of noncovalent attractive interactions has been examined, but such supramolecular networks held by attractive interactions are susceptible to surrounding environments and may readily decompose upon slight condition changes. To obtain robust cluster networks applicable in various fields, covalent crosslinking between the clusters would be desirable. In this work, we report the synthesis of covalently crosslinked gold-cluster networks by using two different methods and discuss their structures and properties.1 For the component of the precursor cluster, Au25(SR)18 cluster was used because it is capable to adopt diverse types of thiolate ligands and has high stability. When the mixture of tetrachloroauric acid, tetraoctylammonium bromide, and 1,6-hexanedithiol (HDT) was reduced by sodium borohydride, monomeric Au25 cluster (1) coordinated by oligodisulfide units derived from HDT was obtained (Figure 1). This Au25 monomer holds free thiolate anions at the outermost of the ligand layer. When the solid sample of 1 was thinly deposited on a glass surface and then treated with O2 for one day, insoluble transparent polymer films (2) were obtained. The absorption spectrum of the film 2 in transmission mode showed a characteristic pattern of anionic [Au25(SR)18]-, indicating the retention of the original Au25S18 framework during the polymerization. Further analyses demonstrated that this polymerization is triggered by oxidative thiyl radical generation from the surface free thiolate anion, followed by radical-mediated dynamic thiolate-disulfide exchange reactions that lead to the extensive networking of the clusters. Meanwhile, when 1 was left in solution under inert atmosphere, spontaneous precipitation of gel-like polymer (3) was observed within 1 h. 3 also showed a characteristic spectrum of Au25S18 cluster, suggesting another type of polymerization without involvement of oxygen occurred in solution. Compositional analysis revealed that this polymerization involves successive intercluster ligand exchange reactions. These two cluster polymers showed different solid structures and adsorption activities towards dye molecules, which would be discussed in terms of the structures and preparation methods.
Cyanoaurate-based Coordination Polymers as Emissive Sensory Materials for Toxic Gases
* Daniel Leznoff, Simon Fraser University, Canada
Cyanometallate coordination polymers – starting with the famous Prussian Blue - have historically been extensively prepared to target a wide range of properties. In particular, linear d10 [Au(CN)2]- and square- planar [Pt(CN)4]2- building blocks have been exploited to take advantage of attractive metal-metal interactions to increase structural dimensionality and access the emissive behaviour that is often associated with such interactions. Our recent results on designing new structurally flexible coordination polymers that incorporate cyanoaurate units with other d10 metals such as Zn(II), Cu(I) and Cd(II) to prepare vapochromic and/or emissive coordination polymers will be presented, as well as their solid-state emission response to exposure to a range of toxic gases, with a particular focus on ammonia and S-donor analytes. The use of a 2nd generation, anionic digold(I)-isomaleonitrile system as an emissive DMF sensor and the sensitivity of the emission of this system to subtle changes in cation will also be examined. Time permitting, patterning of cyanoaurate coordination polymers using redox coordination will also be described.