Molecular clusters as structural constituents for soft material designs: tunable viscoelasticity and multi-functional integrations

Inorganic materials are usually limited to powdered or crystalline forms which compromises their processability into monoliths with continuous structures and thus hinders their practical applications. Molecular clusters (MCs), a class of ultra‑small inorganic species, are now recognized as promising structural units for material designs. The inorganic functionalities are well preserved while bonused polymer-like mechanical flexibility and processability can be achieved. This review focuses on this nascent field and systematically summarizes recent progress in the construction of functional soft materials assembled from MC constituents. The size effects and hierarchical dynamics behaviors of MC systems are discussed in detail, which establishes the physical foundation for their use as structural units in soft materials. Programmable structural design strategies are also covered, as manifested in the evolution from mimicking the polymer chain structures to moving beyond the framework of long-chain topology designs. The discussion subsequently turns to functional integrations and performance breakthroughs in areas such as adsorption/separation, ion conduction, and impact resistance. Finally, it concludes with an overview of the key challenges, along with a rational outlook on future research direction. We anticipate that this emerging class of materials will not only overcome the long-standing mechanical limitations of inorganic materials but also open new avenues for the design of functional materials beyond existing paradigms.