Seed‐Controlled Gel‐to‐Single‐Crystal Transformation in the Supramolecular Co‐assembly of Metal–Organic Polyhedra and Redox‐Active Cu(II) Complex

Rational molecular design is paramount for comprehending hierarchical self‐assembly processes. While current approaches have primarily focused on π‐chromophore‐based systems, there is limited understanding about the self‐assembly of metal–organic polyhedra (MOP). In this study, the co‐assembly between Ga III ‐based metal–organic cubes ( Ga‐MOC s) ([Ga 8 (ImDC) 12 ] 12− ) (ImDC = imidazoledicarboxylate) and [Cu(en) 2 (H 2 O) 2 ] 2+ ( Cu‐en ) binder is exploited via charge‐assisted hydrogen bonding (CAHB) interactions at low concentration to regulate supramolecular polymerization. Employing a sequential growth control approach, precise tuning over the supramolecular co‐assembly is enabled. At higher concentrations, the supramolecular polymer fibers entangle to form a hydrogel. Notably, the kinetically metastable gel state spontaneously transforms into a thermodynamically stable cubic crystal within 17 days, driven by the nanofiber bundling. A seeded approach is utilized to regulate the time scale, accelerating the kinetics and reducing the transformation period from 17 days to 8 h. The excellent processable redox‐active GaCu assembly demonstrates notable performance in electrochemical CO 2 reduction, showing high Faradaic efficiency and stability for CO production, supported by in situ spectroscopy and DFT calculations. This study demonstrates unprecedented high‐precision control over nanostructure and transition rates from kinetic to thermodynamic assembly in a MOP‐based supramolecular system and highlights the pivotal role of redox‐active, processable soft materials in CO 2 valorization.