2D Covalent Organic Frameworks with cem Topology

A large number of covalent organic frameworks (COFs) with two-dimensional (2D) layered structures have been reported, but their network structures are restricted to only seven topologies (namely, hcb, hxl, kgm, sql, tth, bex, and kgd) because of the limited choice of building blocks. In this work, we illustrate how linking pseudo-fivefold symmetric 1,2,3,4,5-penta(4-formylphenyl)pyrrole with linear aromatic diamines through dynamic imine bonds produces three 2D porous COFs with an unprecedented cem topology, which represent the first examples of five-vertex semiregular Archimedean tessellations in COFs. The three 2D COFs are isostructural, and each adopts an eclipsed stacking structure with unidirectional hierarchical pores, in which the pyrrole unit is utilized as the five-vertex of network to form both square and triangular pores in a 3(3).4(2) sequence. With high thermal and chemical resistances, the COF-packed HPLC columns show excellent performance to provide separation of 10 different polycyclic aromatic hydrocarbons, a group of the most widespread organic environmental pollutants. The implementation of five-vertex Archimedean tessellations thus couriers a strategy to design COFs with new topologies and paves a new way to expand the inimitable properties of COF materials.