Triptycene-Based 2.5-Dimensional Metal–Organic Frameworks: Atomically Accurate Structures and Anisotropic Physical Properties from Hydrogen-Bonding Bridged Protonated Building Units

Recent advances in two-dimensional (2D) π-d conjugated conductive metal–organic frameworks (2D cMOFs) have highlighted their potential as sophisticated, active materials in electrochemical energy storage devices, electrocatalysis, and sensors. However, a lack of high-quality structural characterization severely limits our understanding of their physical properties. Specifically, rapid and irreversible nucleation and aggregation, induced by strong interlayer π-π interactions, have hindered crystal growth in these cMOFs. In this study, by utilizing triptycene-based ligands, 2,3,6,7,14,15-hexahydroxy triptycene (HHTripH2) and 9,10-dimethyl-2,3,6,7,14,15-hexahydroxy triptycene (HHTripMe2), we successfully mitigated interlayer π-π interactions and achieved SCXRD quality crystals of two triptycene-based 2D MOFs/Cu3(TripH2)2 and Cu3(TripMe2)2. The crystal structures reveal a protonated catechol ligand and an interlayer hydrogen-bonding-guided stacking motif, with density functional theory (DFT) calculations confirming their semiconducting nature. The steric effect of the two axial methyl groups in the TripMe2 ligand modifies the structure of Cu3(TripMe2)2 from regular AB stacking to interpenetration, significantly enhancing the stability of the crystals. These high-quality crystals enabled the direct measurement of anisotropic dual proton–electron conduction, governed by thermally activated hopping through hydrogen-bonding networks. ESR and susceptibility measurements indicate that these modifications facilitate hydrogen-bonding-guided One-dimensional (1D) antiferromagnetic behavior in the Cu(cat)2 secondary building units (SBUs). This study reveals the critical roles of high-quality crystal structures and protonation–deprotonation of coordinating atoms in understanding the properties of 2D MOFs.