Proton Conduction in Stable, Crystalline, and Porous Hydrogen-Bonded Metal-Organic Frameworks

Hydrogen-bonded metal-organic frameworks (HMOFs) represent a novel class of crystalline materials that integrate hydrogen bonds (HBs) and coordination bonds (CBs) within stable structures. Herein, we designed carbonyl-rich molecules with extended arms to increase the density of hydrogen-bond acceptors and enhanced benzene ring rotation to reduce π-π stacking, thereby strengthening hydrogen bonding to assist coordination-driven assembly of HMOFs. Benefiting from strong hydrogen bonding between central carbonyl groups and metal ions to modulate metal coordination, a series of 2+2 layer-interpenetrated HMOFs with different metal nodes (Co²⁺, Ni²⁺, and Zn²⁺) were synthesized. Serving as interpenetration intersections, those metal nodes stabilize the framework via hydrogen bonding, together with the inter-locked coordination framework and extensive hydrogen-bonded network, endow the HMOFs with open channels and qualified stability. These HMOFs exhibit proton conductivity of ∼10^-3 S cm^-1 at 95°C and 98% relative humidity with activation energies all below 0.2 eV. This study presents a new approach for directly constructing stable HMOFs using carbonyl-rich planar ligands, providing valuable insights for the rational design and synthesis of stable, highly crystalline frameworks.