Metal-Organic Frameworks (MOFs), known for their high porosity and customizable structures, have emerged as ideal platforms for stabilizing metal nanomaterials. Various noble metal nanoparticle (NP)/nanocluster (NC) systems embedded within MOFs have been developed for catalytic applications, such as Ag/Au NPs within ZIF-8, MOF-5, and MIL-101. Compared to NPs, NCs, as a series material possess atomically precise structures, unique electronic properties, and potential for a wide range of applications.  

Ag cluster-based MOFs (CMOFs) have garnered significant attention for combining the advantages of both clusters and MOFs, such as tunable structures, adjustable pore sizes, and diverse electronic properties, are considered ideal systems for such investigations. Recent studies have reported numerous coinage metal clusters serving as secondary building units (SBUs). The first assembly material based on silver clusters was constructed using 4,4′-dipyridine as a linker. Subsequently, leveraging the ease of assembly and disassembly, various silver clusters—including Ag8, Ag10, Ag12, Ag14, Ag15, Ag18, and Ag27—have been integrated into 1-periodic, 2-periodic, and 3-periodic CMOFs with organic linkers, demonstrating applications in catalysis, radiometric oxygen sensing, and more. Beyond these applications, a chiral memory effect has been observed in a 3D Ag14-based CMOF. Additionally, inorganic anions such as NO3− and SbF6− have enabled the assembly of the [Au1Ag22(S-Adm)12]3+ (S-Adm = 1-adamantanethiol) cluster into 3D frameworks using SbF6− linkers. Understanding the connection between the cluster-building units and the linkers is crucial in the design and engineering of CMOFs and further promising applications. 

In the past few decades, researchers have developed and reported numerous Au nanoclusters (NCs) protected by phosphines, thiols, and alknyls ligands. Multiple studies have explored their potential applications in various fields, including biomedicine and catalysis due to their ultra-small sizes, defined structures, and unique electronic properties. Recently, N-heterocyclic carbene (NHC) have emerged as a valuable ligand due to their strong coordination on the surface of Au NCs as well as nanoparticles (NPs). The use of NHCs, as stabilizing capping ligands for Au NCs, holds great promise in addressing some challenges such as achieving stable and water-soluble NCs, owing to the possibility of functionalizing these ligands with various groups. 

Au25, a well-known Au NC, has been utilized within several MOFs, typically, ZIF-8 and UiO-66 systems. Under the protective layer of UiO-66, Au25 NCs demonstrate superior oxidative esterification activity and stability in furfural compared to pristine Au25 NCs. Furthermore, covalent bonding between Au25 and UiO-66 significantly enhances catalytic performance compared to physical mixing, underscoring the advantages of covalent NC@MOF materials. Even though [Au25(p-HMBA)18]− (p-H2MBA = 4-mercaptobenzoic acid) has recently developed as MOFs with several metal ions, designing a suitable Au NCs system as MOF building blocks remains a significant challenge.