Comprehensive and practical guidelines for reduction synthesis of atomically precise coinage-metal nanoclusters

As a model system for studying the structure-and-property relationship and surface coordination chemistry of metal nanomaterials, ligand-stabilized atomically precise coinage-metal (Au, Ag, Cu) nanoclusters have attracted bolstering attention. Considerable effort has been extended to the synthesis and structure determination of metal nanoclusters in the past decades, in which chemical reduction of high-valence metal ions in the presence of protective ligands lays the foundation. After analyzing over 200 synthetic examples of individual metal nanoclusters prepared by direct reduction method, with the reactants of either single kind metal of Au, Ag, Cu or alloying (e.g., Au-Ag, Au-Pt), as well as ligands of phosphines, thiolates, alkynyls, N-heterocyclic carbenes, halides and their combinations, we propose comprehensive and practical guidelines for reduction synthesis of ligand-stabilized metal nanoclusters. This Review seeks to elucidate the prospective introduction of robust synthetic prototypes for engineering ligand-stabilized metal nanoclusters, which have evolved from one-phase, two-phase, miscible solution synthesis to solid-state synthesis. Several factors are key for synthesis optimization, mainly including a selection of precursors, reductant systems, as well as purification strategies. After providing an expansive and critical viewpoint on this rapidly evolving field, some promising trends in future are prospected in the end.