Magic number metal nanoclusters are atomically precise nanomaterials that have enabled unprecedented insight into structure-property relationships in nanoscience. Thiolates are the most common ligand, binding to the cluster via a staple motif in which only central gold atoms are in the metallic state. The lack of other strongly-bound ligands for nanoclusters with different bonding modes has been a significant limitation in the field. Herein, we report a previously unknown ligand for gold (0) nanoclusters: N-heterocyclic carbenes (NHCs), which feature a robust metal-carbon single bond, and impart high stability to the corresponding gold cluster. The addition of a single NHC to gold nanoclusters results in significantly improved stability and catalytic properties in the electrocatalytic reduction of CO2. By varying the conditions, nature and number of equivalents of the NHC, predominantly or exclusively monosubstituted NHC-functionalized clusters result. Clusters can also be obtained with up to five NHCs, as a mixture of species.

Highly stable gold nanoparticles (Au NPs) functionalized by bidentate N-heterocyclic carbene (NHC) ligands have been synthesized by top-down and bottom-up approaches. A detailed study of the effect of alkylation, denticity, and method of synthesis has led to the production of NHC-stabilized nanoparticles with higher thermal stability than bi- and tridentate thiol-protected Au NPs and than monodentate NHC-stabilized NPs. Importantly, bidentate NHC-protected NPs also displayed unprecedented stability to external thiol, which has been an unsolved problem to date with all nanoparticles. Thus, multidentate NHC ligands are an important, and as yet unrecognized, step forward for the preparation of high stability nanomaterials.

NHC-Au complexes were used to prepare stable, water-soluble, NHC-protected gold nanoparticles. The water-soluble, charged nature of the nanoparticles permitted analysis by polyacrylamide gel electrophoresis (PAGE), which showed that the nanoparticles were highly monodisperse, with tunable core diameters between 2.0 and 3.3 nm depending on the synthesis conditions. Temporal, thermal, and chemical stability of the nanoparticles were determined to be high. Treatment with thiols caused etching of the particles after 24 h; however larger plasmonic particles showed greater resistance to thiol treatment. These water-soluble, bio-compatible nanoparticles are promising candidates for use in photoacoustic imaging, with even the smallest nanoparticles giving reliable photoacoustic signals.

Herein we report the first chiral Au 10 nanoclusters stabilized by chiral bis N-heterocyclic carbene (bisNHC) ligands. ESI-MS and single-crystal X-ray crystallography confirmed the molecular formula to be [Au 10 (bisNHC) 4 Br 2 ](O 2 CCF 3 ) 2 . The chiral Au 10 nanocluster adopts a linear edge-shared tetrahedral geometry with a prolate shape. DFT calculations provide insight into the electronic structure, optical absorption, and circular dichroism (CD) characteristics of this unique Au 10 nanocluster. CD spectra demonstrate chirality transfer from the chiral bisNHC ligand to the inner Au 10 nanocluster core. Examination of ESI-MS and UV− vis spectra show that cluster [Au 9 (bisNHC) 4 Br]Br 2 is formed initially and then transformed into the Au 10 nanocluster in solution.

NHC-Au I complexes were used to prepare stable, water-soluble,N HC-protected gold nanoparticles.T he watersoluble,charged nature of the nanoparticles permitted analysis by polyacrylamide gel electrophoresis (PAGE), whichshowed that the nanoparticles were highly monodisperse,with tunable core diameters between 2.0 and 3.3 nm depending on the synthesis conditions.T emporal, thermal, and chemical stability of the nanoparticles were determined to be high. Treatment with thiols caused etching of the particles after 24 h; however larger plasmonic particles showed greater resistance to thiol treatment. These water-soluble,b io-compatible nanoparticles are promising candidates for use in photoacoustic imaging, with even the smallest nanoparticles giving reliable photoacoustic signals.Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.

Magic number metal nanoclusters are atomically precise nanomaterials that have enabled unprecedented insight into structure-property relationships in nanoscience. Thiolates are the most common ligand, binding to the cluster via a staple motif in which only central gold atoms are in the metallic state. The lack of other strongly-bound ligands for nanoclusters with different bonding modes has been a significant limitation in the field. Herein, we report a previously unknown ligand for gold (0) nanoclusters: N-heterocyclic carbenes (NHCs), which feature a robust metal-carbon single bond, and impart high stability to the corresponding gold cluster. The addition of a single NHC to gold nanoclusters results in significantly improved stability and catalytic properties in the electrocatalytic reduction of CO₂. By varying the conditions, nature and number of equivalents of the NHC, predominantly or exclusively monosubstituted NHC-functionalized clusters result. Clusters can also be obtained with up to five NHCs, as a mixture of species.

The preparation of a novel Au6 cluster bearing a bidentate mixed carbene–thiolate ligand is presented.

Small and cool: The mechanism of formation of amine-capped Pd nanoparticles from [Pd(acac)(2)] (acac=acetylacetonate) is elucidated, and shown to involve Pd-amido and Pd-hydride intermediates. The addition of a Lewis base results in a significant reduction in the temperature at which highly monodisperse nanoparticles are isolated.