Chemically Modified Gold/Silver Superatoms as Artificial Elements at Nanoscale: Design Principles and Synthesis Challenges.

Pure and doped gold/silver clusters protected by monolayers of organic ligands have attracted much interest as novel functional materials owing to their nonbulk-like, size-specific properties. They can be viewed as chemically modified superatoms because their stabilities and properties are governed by the electron shell configurations of the Au/Ag cores. Chemically modified superatoms are unique from conventional atoms in that they have additional control parameters such as surface modification, compositions, atomic packing, and size, although both of them follow similar Aufbau principles. Atomically precise synthesis and structure determination by X-ray crystallography have deepened our understanding of the correlation between the structures and fundamental properties of the superatoms. However, remaining challenges for the exploration of novel materials using superatoms as artificial elements at the nanoscale include (1) establishment of guiding principles of the electronic structures and (2) development of efficient, targeted synthesis according to rational design guidelines for functionalities. To address the first task, we herein propose and rationalize empirical guiding principles of electronic structures using icosahedral Au/Ag superatoms with the closed electron configuration as platforms. The second task is addressed by proposing design guidelines for functionalities and hydride-mediated transformation processes for efficient, targeted synthesis. These efforts will lead to the construction of a new periodic table of chemically modified superatoms and open up a materials world of quasi-molecules made of superatoms. We hope that this Perspective will contribute to the creation of a new paradigm based on superatoms, which parallels the matured world of molecular science.