Polymorphism of 2D Imine Covalent Organic Frameworks.

We designed and synthesized A2 B2 type tetraphenyl benzene monomers (p-, m-, and o-TetPB) which have the para-, meta, and ortho-substituted isomeric structures, for the direct construction of isomeric frameworks. Interestingly, both kagome (kgm) and monoclinic square (sql) framework isomers are produced from either p-TetPB (C2h symmetry) or m-TetPB (C2v symmetry) by changing reaction solvents, while their isomeric structures are characterized by X-ray diffraction, computational simulation, microscopy, and sorption isotherm measurements. Only sql frameworks was formed for o-TetPB (C2v symmetry), irrespective of reaction solvents. These results disclose a unique feature in the framework structural formation, that is, the geometry of monomers directs and dominates the lattice growth process while the solvent plays a role in the perturbation of chain growth pattern. The isomeric frameworks exhibit highly selective adsorption of vitamin B12 owing to pore shape and size differences.