Molecule-like synthesis of ligand-protected metal nanoclusters

Ligand-protected metal nanoclusters (NCs) are ultrasmall particles (<3 nm) that represent the molecular state of metal materials. Owing to their molecule-like structure — particularly their atomic precision and protein-like hierarchy — metal NCs feature numerous useful molecule-like properties, including discrete energy levels, strong luminescence, intrinsic magnetism and programmable catalytic activity. In this Review, by regarding metal NCs as metallic analogues of organic molecules, we summarize methodological and mechanistic advances in their precise synthesis at the molecular and atomic levels. We first decipher cluster structure based on a protein-like hierarchical scheme and discuss synthetic strategies that realize molecular monodispersity in these clusters. We resolve formation mechanisms of metal NCs at the molecular level, aiming to establish step-by-step reaction maps reminiscent of total synthesis routes of organic molecules. We then examine approaches to customize the composition and morphology of the metal core, metal–ligand interface and ligand shell at the atom level. This Review concludes with our perspectives on the future development of atomic precision chemistry in both metal NCs and other inorganic nanomaterials.