Electrically conducting 2D metal–organic frameworks (MOFs) have attracted considerable interest, as their hexagonal 2D lattices mimic graphite and other 2D van der Waals stacked materials. However, understanding their intrinsic properties remains a challenge because their crystals are too small or of too poor quality for crystal structure determination. Here, we report atomically precise structures of a family of 2D π-conjugated MOFs derived from large single crystals of sizes up to 200 μm, allowing atomic-resolution analysis by a battery of high-resolution diffraction techniques. A designed ligand core rebalances the in-plane and out-of-plane interactions that define anisotropic crystal growth. We report two crystal structure types exhibiting analogous 2D honeycomb-like sheets but distinct packing modes and pore contents. Single-crystal electrical transport measurements distinctively demonstrate anisotropic transport normal and parallel to the π-conjugated sheets, revealing a clear correlation between absolute conductivity and the nature of the metal cation and 2D sheet packing motif.
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This work was supported by the Army Research Office (grant number W911NF-17-1-0174). J.S. thanks National Natural Science Foundation of China (grant number 21527803,21621061) and Ministry of Science and Technology of China (grant number 2016YFA0301004). The staff of beamlines BL17B1 and BL19U1 of the National Facility for Protein Science Shanghai (NFPS) at the Shanghai Synchrotron Radiation Facility (SSRF) are acknowledged for their assistance in the data collection. Aberration-corrected TEM was carried out at the Center for Functional Nanomaterials (CFN), Brookhaven National Laboratory (BNL), which is supported by the US Department of Energy. Cryo-EM was carried out at the Automated Cryogenic Electron Microscopy Facility in MIT.nano. Use of the Advanced Photon Source (APS) at Argonne National Laboratory (ANL) and ANL’s contribution were supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract no. DE-AC02-06CH11357. MRCAT operations, beamline 10-BM, are supported by the Department of Energy and the MRCAT member institutions. Part of the characterization and device fabrication was performed at the Harvard Center for Nanoscale Systems (CNS), a member of the National Nanotechnology Infrastructure Network (NNIN), which is supported by the National Science Foundation under NSF award no. ECS-0335765. Computational work was performed in the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by the NSF (ACI-105357), and was supported by the Division of Materials Research under grant no. DMR-1956403. Y.L. thanks the Swedish Research Council and the Knut and Alice Wallenberg Foundation (KAW). J.-H.D. thanks W. S. Leong, R. W. Day and D. Zakharov for their assistance with electron-beam device fabrication and HRTEM data collection.
The authors declare no competing interests.
Peer review information Nature Materials thanks Albert Talin and the other anonymous reviewers for their contribution to the peer review of this work.
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Dou, JH., Arguilla, M.Q., Luo, Y. et al. Atomically precise single-crystal structures of electrically conducting 2D metal–organic frameworks. Nat. Mater. (2020). https://doi.org/10.1038/s41563-020-00847-7
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