Control of Extrinsic Porosities in Linked Metal-Organic Polyhedra Gels by Imparting Coordination-Driven Self-Assembly with Electrostatic Repulsion.

The linkage of metal-organic polyhedra (MOPs) to synthesize porous soft materials is one of the promising strategies to combine processability with permanent porosity. Compared to the defined internal cavity of MOPs, it is still difficult to control the extrinsic porosities generated between crosslinked MOPs because of their random arrangements in the networks. Herein, we report a method to form linked MOP gels with controllable extrinsic porosities by introducing negative charges on the surface of MOPs that facilitates electrostatic repulsion between them. A hydrophilic rhodium-based cuboctahedral MOP (OHRhMOP) with 24 hydroxyl groups on its outer periphery can be controllably deprotonated to impart the MOP with tunable electrostatic repulsion in solution. This electrostatic repulsion between MOPs stabilizes the kinetically trapped state, in which an MOP is coordinated with various bisimidazole linkers in a monodentate fashion at a controllable linker/MOP ratio. Heating of the kinetically trapped molecules leads to the formation of gels with similar colloidal networks but different extrinsic porosities. This strategy allows us to design the molecular-level networks and the resulting porosities even in the amorphous state.