N-Heterocyclic carbenes (NHCs) have emerged as a new class of ligands for materials chemistry that appears particularly relevant for the stabilization and functionalization of metal nanoparticles (NPs). The particular properties and high synthetic flexibility of NHCs make them highly attractive tools for the development of new (nano)materials and the fundamental study of their properties. The relationships between the NHC structure and NP structure/properties, including physical, biological, and self-assembly properties, remain largely unknown. In the past decade, many efforts have been made to gain more fundamental understanding in this area. In this feature article, we present our contribution in this field focusing on the formation of NHC-coated Au nanocrystals (NCs), their stability, and their ability to self-assemble into 3D crystalline structures called supracrystals. First, the formation of NHC-stabilized Au NCs is discussed by comparing different NHC structures, NHC-based Au precursors, and synthesis methods. This study shows the major role of the NHC structure in obtaining both stable NHC-coatedAu NCs and narrow size distributions. In a second part, a comparativestudy of the oxygen resistance of NHC- and thiol-coated NCs is presented,demonstrating the enhanced stability of NHC-coated Au NCs to oxygen-basedtreatments. Finally, the self-assembly of NHC-coated Au NCs into 3DAu superlattices is presented. The formation of large organized domainsof several micrometers is described from the design of NHCs tailoredwith long alkyl chains. In these different contexts, efforts havebeen made to gain a more in-depth understanding of the behavior ofNHC ligands at the surface of NCs. These results show that the NHC-basedapproach to nanomaterials has many assets for opening a new researcharea in the supracrystal world.
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