Twist Building Blocks from Planar to Tetrahedral for the Synthesis of Covalent Organic Frameworks.

Rational construction of covalent organic frameworks (COFs) with novel structures still remains a challenge. Herein, we report the designed synthesis of two COFs, 2D-BPTA-COF and 3D-BMTA-COF, starting from biphenyl-based precursors but with different groups at the ortho positions. Both COFs exhibited high crystallinity and large surface area, and interestingly, 2D-BPTA-COF crystallizes into 2D sheets with AB stacking mode while 3D-BMTA-COF adopts a 7-fold interpenetrated structure with topology. This structural difference could be ascribed to the introduction of methyl groups in the building blocks, as the dihedral angle of biphenyl rings in 2D-BPTA-COF is ∼0° while in 3D-BMTA-COF it is ∼60°. Therefore, it is possible to synthesize COFs with different structures by twisting building blocks from planar to tetrahedral with steric hindrance. We believe this result represents a general and straightforward way to expand the diversity of tetrahedral nodes for constructing 3D COFs in the future, and moreover, a new tetrahedral node for constructing 3D COFs is now available.