As a model system for studying the structure–property relationship and surface coordination chemistry of metal nanomaterials, ligand-stabilized, atomically precise coinage–metal (Au, Ag, and Cu) nanoclusters (NCs) have attracted considerable attention. Extensive effort has been devoted to the synthesis and structural determination of metal NCs over the past decades, with the chemical reduction of high-valence metal ions in the presence of protective ligands laying the foundation. After examining over 200 synthetic examples of individual metal NCs prepared through direct reduction methods—using reactants such as single metals (Au, Ag, and Cu) or alloys (e.g., Au-Ag, Au-Pt), along with ligands such as phosphines, thiolates, and alkynyls, N-heterocyclic carbenes, halides, and their combinations, we propose comprehensive and practical guidelines for the reduction synthesis of ligand-stabilized metal NCs. This review aims to elucidate the potential introduction of robust synthetic prototypes for engineering these NCs, which have evolved from one-phase, two-phase, and miscible solution synthesis to solid-state synthesis. Several factors are crucial for optimizing synthesis, including the selection of precursors, reductant systems, and purification strategies. After presenting an expansive and critical perspective on this rapidly evolving field, we outline some promising future trends.

The detailed elucidation of structure–property relationships at the molecular level in metal nanoclusters is highly valuable for advancing structure design and optimizing performance. However, effectively manipulating metal nanoclusters’ physical and chemical properties at the single-molecule level remains a significant challenge. Here, we demonstrate that single-molecule chemistry can effectively control the third-order nonlinear optical (NLO) performance of structurally precise copper nanoclusters. We present two analogous clusters, [Cu₂₅(RS)₁₈H₁₀]³⁻ (Cu₂₅) and [Cu₂₆(RS)₁₈H₁₀(PPh₃)]²⁻ (Cu₂₆, where RSH is 2-fluorobenzenethiol), whose structures were determined in this study. Both clusters feature a Cu₁₃ core in a centered cuboctahedron configuration with similar shell structures. However, Cu₂₆ includes an additional PPh₃Cu⁺ unit. This single structural difference significantly changes their properties, including optical characteristics and stability. Compared to Cu₂₅, Cu₂₆ exhibits enhanced optical limiting (OL) activity. Theoretical calculations indicate that the substantial electron transfer from the PPh₃ ligand to the metal core enhances the NLO performance of Cu₂₆. This study highlights the potential of structurally precise copper nanoclusters as OL materials and advances the understanding of nanoparticulate material fabrication using a single-molecule strategy.