Harnessing Interpenetration for High Proton Conductivity in Zirconium Metal-Organic Frameworks

While interpenetration has emerged as a powerful strategy for engineering pore geometry and introducing synergistic functionality, its specific role in enhancing proton conduction has remained unexplored. Herein, we report the rational design and synthesis of two new isomeric Zr-MOFs, denoted IAM-12 and IAM-13, constructed from pyrrolo-pyrrole-based tetratopic linkers (H₄L₁ and H₄L₂). Both MOFs possess the same 4,8-connected scu topology, along with unexpected 2-fold interpenetrated frameworks. Single-crystal X-ray diffraction analysis reveals that interpenetration arranges the terminal H₂O/OH^- moieties from the Zr₆ nodes of two independent subnets in an alternating up-and-down fashion along the confined one-dimensional channels. This spatial arrangement significantly reduces the interframework O···O distances, facilitating the formation of dense, well-defined H-bonding networks with lattice water molecules. Consequently, the MOFs exhibit exceptionally high intrinsic proton conductivities of 1.05 × 10^-2 S·cm^-1 for IAM-12 and 8.82 × 10^-3 S·cm^-1 for IAM-13 at 85 °C and 95% RH, respectively. These values allow IAM-12 and IAM-13 to rival those of renowned MOFs that exhibit high proton conductivity through functionalization or postmodification. This work demonstrates that rational geometric control via interpenetration is a powerful, yet underexplored, strategy for the design of advanced proton-conducting MOFs, moving beyond a reliance solely on chemical functionalization.