Covalent organic frameworks (COFs) are among the fastest-growing classes of materials with an almost unlimited number of achievable structures, topologies, and functionalities. The exact structure of layered COFs is, however, hard to determine due to an often significant mismatch between experimental powder X-ray diffraction (PXRD) pattern and predicted geometries. We attribute these discrepancies to an inherent disorder in the stacking of layered COFs, invalidating standard theoretical three-dimensional (3D) models. We have represented the structures of COF-1, COF-5, and ZnPc-pz by stacking layers following the Maxwell–Boltzmann energy distribution of their stacking modes. The simulated PXRD patterns of the statistical COF models are close to the experimental ones, featuring an unprecedented agreement in peak intensity, width, and asymmetry. The rarely considered ABC stacking mode proved to be important in layered COFs, as well as including solvent molecules. Our model also shows several general features in PXRD originating from the stacking disorder.

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Two-dimensional conjugated metal-organic frameworks (2D c-MOFs) have attracted increasing interests for (opto)-electronics and spintronics. They generally consist of van der Waals stacked layers and exhibit layer-depended electronic properties. While considerable efforts have been made to regulate the charge transport within a layer, precise control of electronic coupling between layers has not yet been achieved. Herein, we report a strategy to precisely tune interlayer charge transport in 2D c-MOFs via side-chain induced control of the layer spacing. We design hexaiminotriindole ligands allowing programmed functionalization with tailored alkyl chains (HATI_CX, X = 1,3,4; X refers to the carbon numbers of the alkyl chains) for the synthesis of semiconducting Ni3(HATI_CX)2. The layer spacing of these MOFs can be precisely varied from 3.40 to 3.70 Å, leading to widened band gap, suppressed carrier mobilities, and significant improvement of the Seebeck coefficient. With this demonstration, we further achieve a record-high thermoelectric power factor of 68 ± 3 nW m−1 K−2 in Ni3(HATI_C3)2, superior to the reported holes-dominated MOFs.

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Despite superb instrumental resolution in modern transmission electron microscopes (TEM), high-resolution imaging of organic two-dimensional (2D) materials is a formidable task. Here, we present that the appropriate selection of the incident electron energy plays a crucial role in reducing the gap between achievable resolution in the image and the instrumental limit. Among a broad range of electron acceleration voltages (300 kV, 200 kV, 120 kV, and 80 kV) tested, we found that the highest resolution in the HRTEM image is achieved at 120 kV, which is 1.9 Å. In two imine-based 2D polymer thin films, unexpected molecular interstitial defects were unraveled. Their structural nature is identified with the aid of quantum mechanical calculations. Furthermore, the increased image resolution and enhanced image contrast at 120 kV enabled the detection of functional groups at the pore interfaces. The experimental setup has also been employed for an amorphous organic 2D material.