Investigation of N-heterocyclic Carbenes as Ligands for Stabilizing Gold Nanoclusters

Abstract

While the development of nanomaterials such as metal nanoparticles, nanowires, carbon nanostructures, and many others have long been reported, one significant obstacle in the advancement of these functional materials remains: precise control over structure and their resulting properties. Almost all nanomaterials are prepared as mixtures and characterized by average bulk size, rather than a molecular formula. This is inherently problematic, since their properties are directly related to their size and molecular structure, leaving a true understanding of structure–property relationships nearly impossible. Ligand protected metal nanoclusters (NCs) are an interesting exception to this. They are atomically precise ultra-small nanoparticles, with diameters less than 3 nm or the equivalent of 3-300 metal atoms. Despite many recent advances in this field, the stability of these materials remains a significant limitation. Fortunately, the stability of these materials can be controlled through the judicious choice of the ligands that protect the surface of the metal core. N-Heterocyclic carbenes (NHCs) have become one of the most widely studied class of ligands in molecular chemistry and have found applications in fields as varied as catalysis, the stabilization of reactive molecular fragments, and biochemistry. More recently, NHCs have found applications in materials chemistry and have allowed for the functionalization of surfaces, polymers, nanoparticles, and discrete, well-defined clusters. In this work, we provide an in-depth investigation and characterization of various NHC ligands to stabilize gold nanoclusters and their resulting properties.