[Au23(SR)16]−: A Stepping Stone towards the Rational Design of Atomically Precise Metal Nanoclusters

Atomically precise metal nanoclusters (MNCs) have revolutionized the field of nanoscience and material chemistry with their well-defined structure, quantum confinement effect, and distinctive physicochemical properties. They have opened up new avenues for applications in diverse fields such as biomedicine, renewable energy devices, catalysis, chemical sensing, etc. These metal NCs with a size range of 1–3 nm stand out from the conventional nanoparticles (1–100 nm) due to the quantum confinement effect, which is absent in the polydisperse nanoparticles. Over the past few decades, a populous library of metal NCs with different metals, such as Au, Ag Cu, and their alloys, has been established. Of all these NCs, the molecularly pure [Au₂₃(CHT)₁₆]⁻ NC (CHT = S-c-C₆H₁₁) is emerging as a potential nanomaterial with a unique structure and properties and is being used as a precursor for various transformation studies. This [Au₂₃(CHT)₁₆]⁻ NC has an Au₁₅ bipyramidal kernel, which can be viewed as an Au₁₃ cuboctahedron capped with two hub Au atoms, protected by a pair of trimeric and monomeric staple motifs and four bridging thiolates. This unique structure of [Au₂₃(CHT)₁₆]⁻ NC gives rise to interesting properties such as photoluminescence (PL) and catalysis. In this Account, we focus on the recent advances in the methods and types of different structural transformations carried out on the [Au₂₃(CHT)₁₆]⁻ NC and their detailed mechanistic insights. These postsynthetic modifications have proven to be efficient strategies to induce structural changes, tune the physicochemical properties, and tailor them for promising applications. We have divided the transformation chemistry of [Au₂₃(CHT)₁₆]⁻ NC into three sections. In the first section, we discuss various types of metal-exchange-induced transformation reactions carried out on the [Au₂₃(CHT)₁₆]⁻ NC with different heterometal ions to achieve bimetallic NCs with various degrees of alloying and multiple alloying sites, whereas the second section deals with the various ligand-exchange-induced transformation reactions of [Au₂₃(CHT)₁₆]⁻ NC, exploring the intriguing ligand effects on the NC structure and properties. Transformation reactions under other conditions, such as irradiation, oxidation, reduction, and change of solvent, are discussed in the last section. A detailed investigation into the mechanistic insights is also discussed to illustrate the driving force and other fundamentals of these transformations. Finally, we outline the future perspectives of the deep exploration of the transformation methods of [Au₂₃(CHT)₁₆]⁻ NC that can advance the NC research. We hope this Account will prompt the nanoscience community to delve deeper into the fundamentals of the synthetic principles and rational design of metal NCs for broader applications.