Probing the Ligand Exchange of N-Heterocyclic Carbene-Capped Ag₂S Nanocrystals with Amines and Carboxylic Acids

Abstract

N-Heterocyclic carbenes (NHCs) are versatile L-type ligands that have been shown to stabilize coinage metal chalcogenide nanocrystals, such as Ag2S, remarkably well. However, very little research has been done on the interaction between NHC ligands and coinage metal chalcogenide nanocrystal surfaces and subsequent ligand exchange reactions. Herein, solution 1H nuclear magnetic resonance methods were used to monitor ligand exchange reactions on stoichiometric Ag2S nanocrystal platforms with various primary amine and carboxylic acid ligands. Despite the introduction of new ligands, the native NHC ligands remain tightly bound to the Ag2S nanocrystal surface and are not displaced at room temperature. Primary amine and carboxylic acid ligands demonstrated quantitative ligand exchange only after the samples had been heated with an excess incoming ligand, which implies a strong NHC-Ag binding energy. Density functional theory affirms that a model NHC ligand binds the strongest to a Ag12S6 cluster surface, followed by amine and carboxylic acid binding; computational analysis is therefore in line with the absence of NHC displacement observed in experiments. Both the bulky sterics of the C14-alkyl chains on the NHC and the high energies for the binding of NHC to the Ag2S surface contribute to the superior colloidal stability over conventional long-chain amine or carboxylic acid ligands (many months vs hours to days).

Thiol-Free Synthesis of Bright Near-Infrared-Emitting Ag2S Nanocrystals through Heterovalent-Metal Decoration for Ecofriendly Solar Cells

“…The other binding site is on one of the Ag atoms relatively far from the decorated metal atom for which the binding energies are displayed by green lines. 36 The binding energy of Ag-oleic acid is marginally impacted, irrespective of the cation impurity types (Figure 4a). In contrast, the binding energy of oleic acid with heterovalent cations increases by ∼24% for Zn, by ∼56% for In and Ga, and by ∼81% for Bi, respectively.…”

“…One binding site is on the decorated homovalent-metal or heterovalent-metal atom for which the binding energies are displayed by red lines. The other binding site is on one of the Ag atoms relatively far from the decorated metal atom for which the binding energies are displayed by green lines …”

Single-gold etching at the hypercarbon atom of C-centred hexagold(I) clusters protected by chiral N-heterocyclic carbenes

“…We previously reported enantiopure NHC-protected asymmetrically twisted CAu I 6 clusters: [(C)(Au I - SS -NHC) 6 ](BF 4 ) 2 and [(C)(Au I - RR -NHC) 6 ](BF 4 ) 2 ( = SS - and RR - 1 NHC , SS -NHC = N , N ’-bis[( S )- α -methylbenzyl]-benzimidazol-2-ylidene, RR -NHC = N , N ’-bis[( R )- α -methylbenzyl]-benzimidazol-2-ylidene) 43 . Although NHCs are generally thought to bind strongly to coinage metal 47 , 48 , we investigated whether etching occurs when bisphosphine is added to NHC-protected CAu I 6 clusters. For example, when 2.5 equiv.…”

Synthesis and disassembly of an organometallic polymer comprising redox-active Co4S4 clusters and Janus biscarbene linkers

“…Some NHC-transition metal complexes and clusters have been shown to undergo exchange with different ligand types as well as other monomeric NHCs. 3,43,44 These reports encouraged us to mix the polymer with a monocarbene in an effort to extract a molecular species. Thus, suspensions of Co 4 S 4 -MCOP in C 6 D 6 were heated with excess Pr i 2 NHCMe 2 (20 equivalents).…”