Making fabric by weaving is known as one of the oldest and most enduring methods. Nevertheless such an important design concept still needs to be emulated in extended chemical structures. Linking molecules into weaving structures would be of a great help to create materials with exceptional mechanical properties and dynamics. For this purpose a woven covalent organic framework-505 (COF-505) has been synthesized using a designed strategy . However, COF-505 is not well crystallized, which gives rise to a poorly resolved PXRD pattern. Therefore, approaches based on electron crystallography methods have been used. The structure of this COF has been solved by a combination of 3D electron diffraction tomography (3D EDT, ), high-resolution TEM imaging and structure modeling.
3D EDT dataset was collected from a single sub-micron crystal in a tilting range of –41.3° to +69.1°. The reconstructed 3D reciprocal lattice was identified as a C-centered orthorhombic Bravais lattice with the unit cell parameters of a = 18.9 Å, b = 21.3 Å, c = 30.8 Å, and V = 12399 Å3, which have been used to index reflections observed in both PXRD pattern and Fourier diffractograms of HRTEM images. The derived reflection conditions were summarized as hkl: h+k = 2n; hk0: h, k = 2n; h0l: h = 2n and 0kl: k = 2n, leading to five possible space groups (s.g.): Cm2a (39), Cc2a (41), Cmca (64), Cmma (67) and Ccca (68). Cm2a, Cmma and Ccca were excluded because their projected plane group symmetries along [1-10] do not coincide with those of the experimental HRTEM images (pgg). Furthermore, by performing Fourier analysis of the HRTEM images and imposing symmetry to the reflections, Cu(I) positions were determined from the reconstructed 3D potential map (Fig. 1). The structure of COF-505 was built in Materials Studio by putting Cu(PDB)2 units at copper positions and connecting them through biphenyl (reacted BZ) molecules. The chemical composition was determined by the elemental analysis, which indicated that the unit-cell framework is constructed by 8 Cu(PDB)2 and 16 biphenyl units (Fig. 2). However, symmetry operations of the s.g. Cmca require two PDB units connected to one copper onto a mirror plane perpendicular to the a–axis that is not the energetically favorable geometry. The final s.g. determined as Cc2a and was used to build and optimize a structure model. The PXRD pattern calculated from the model is consistent with the experimental pattern of activated COF-505.
Grants from Swedish Research Council/VR (Y.M. and P.O.) and JEOL Ltd, Japan (P.O.); EXSELENT and 3DEM-Natur, Sweden (O.T.) and BK21Plus, Korea (O.T.).
 Y. Liu, Y. Ma, Y. Zhao, X. Sun, F. Gandara, H. Furukawa, Z. Liu, H. Zhu, C. Zhu, K. Suenaga, P. Oleynikov, A. S. Alshammari, X. Zhang, O. Terasaki, O. M. Yaghi. Weaving of organic threads into a crystalline covalent organic framework. Science, 351 (2016) 365–369.
 M. Gemmi, P. Oleynikov. Scanning reciprocal space for solving unknown structures: energy filtered diffraction tomography and rotation diffraction tomography methods. Z. Krist. 228 (2013) 51–58.
To cite this abstract:Yuzhong Liu, Yanhang Ma, Yingbo Zhao, Peter Oleynikov, Osamu Terasaki, Omar Yaghi; First woven covalent organic framework solved using electron crystallography. The 16th European Microscopy Congress, Lyon, France. https://emc-proceedings.com/abstract/first-woven-covalent-organic-framework-solved-using-electron-crystallography/. Accessed: October 21, 2021
EMC Abstracts - https://emc-proceedings.com/abstract/first-woven-covalent-organic-framework-solved-using-electron-crystallography/