Single-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 single-crystalline COF (scCOF) with nbo topology, constructed from a rigid square-planar monomer, tetracyclopentatetraphenylene (TCTP), and spiroborate linkages. Theoretical calculations revealed that the TCTP core possesses 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 non-interpenetrated cubic framework with space group Im -3 m . TCTP-COF exhibits high crystallinity, thermal stability up to 320 °C, and permanent porosity with a Brunauer–Emmett–Teller surface area of 1360 m 2 ·g –1 . To the best of our knowledge, this work represents the first structural determination of a spiroborate-linked 3D scCOF using electron diffraction methods, providing a new design strategy for expanding the chemical space of highly ordered 3D COF architectures.