Binder-Mediated Supramolecular Polymerization with Controllable Gel-to-Crystal Transformation in Metal-Organic Polyhedra

Controlling supramolecular polymerization across various length scales through metal-organic polyhedra in aqueous media enables functional nanomaterial fabrication beyond traditional π-chromophoric systems. Herein, we present a straightforward strategy to tune the nano- and microscopic structural evolution of a co-assembled system. Ga-MOC ([Ga₈(ImDC)₁₂]^12-, ImDC = imidazoledicarboxylate) is introduced as a discrete unit, while the Ni-ethylenediamine complex [Ni(en)₃]²⁺ (Ni-en), served as the binder towards supramolecular polymerization. Comprehensive investigations revealed that adjusting the binder ratio in the bicomponent (Ga-MOC and Ni-en) co-assembly process allows precise control over nanostructure length and evolution by influencing both the kinetics and thermodynamics of the assembly. At higher concentrations, this assembly forms a hydrogel above a critical binder ratio. Furthermore, the binder's ratio significantly influences the viscoelastic strength of the hydrogels by modulating the connectivity between the MOCs through hydrogen (H)-bonding. Intriguingly, the hydrogels gradually transformed into crystals without any external stimuli, with different timescales regulated by the binder ratio. Single crystal structure determination reveals a 3D structure composed of Ga-MOC and Ni-en, extended through charge-assisted H-bonding (CAHB) interactions, resulting through the transformation from a kinetically controlled gel state to a thermodynamically stable crystal product. This study provides an understanding of binder-mediated control over nanostructural evolution in co-assembled MOCs.