Toward Controlling the Electronic Structures of Chemically Modified Superatoms of Gold and Silver

Atomically precise gold/silver clusters protected by organic ligands L, [(Au/Ag)xLy]z, have gained increasing interest as building units of functional materials because of their novel photophysical and physicochemical properties. The properties of [(Au/Ag)xLy]z are intimately associated with the quantized electronic structures of the metallic cores, which can be viewed as superatoms from the analogy of naked Au/Ag clusters. Thus, establishment of the correlation between the geometric and electronic structures of the superatomic cores is crucial for rational design and improvement of the properties of [(Au/Ag)xLy]z. This review article aims to provide a qualitative understanding on how the electronic structures of [(Au/Ag)xLy]z are affected by geometric structures of the superatomic cores with a focus on three factors: size, shape, and composition, on the basis of single‐crystal X‐ray diffraction data. The knowledge accumulated here will constitute a basis for the development of ligand‐protected Au/Ag clusters as new artificial elements on a nanometer scale. Ligand‐protected Ag/Au clusters showing novel properties can be viewed as chemically modified superatoms in terms of the electronic structures. This review summarizes the current understanding on the correlation between the electronic structures and key structural factors of the superatoms such as size, shape, and composition toward better control of the properties.