Crystalline 3D covalent organic frameworks with nbo topology

Three-dimensional covalent organic frameworks (3D COFs) are promising crystalline porous materials, but the elucidation of their structure remains challenging, particularly for those featuring spiroborate linkages. Herein, we report the synthesis of a 3D crystalline COF with nbo topology, constructed from a rigid square-planar monomer, tetracyclopentatetraphenylene (TCTP), and spiroborate linkages. Theoretical calculations revealed that the TCTP core has higher rigidity than phthalocyanine, effectively suppressing structural fluctuations during framework formation. The structure of the resulting TCTP-COF was successfully determined using microcrystal electron diffraction (MicroED), revealing a noninterpenetrated cubic framework. TCTP-COF exhibits high crystallinity, thermal stability up to 320°C, and permanent porosity with a Brunauer-Emmett-Teller surface area of 1360 square meters per gram. This work represents the structural determination of a spiroborate-linked 3D crystalline COF using MicroED methods, providing a design strategy for expanding the chemical space of highly ordered 3D COF architectures.