Tuning the Topology of Three-Dimensional Covalent Organic Frameworks via Steric Control: From pts to Unprecedented ljh

Abstract

Whether or not the topology of three-dimensional covalent organic frameworks (3D COFs) can be tuned via steric control remains a big question and has never been reported. Herein, we describe the designed synthesis of two highly crystalline 3D COFs (3D-TPB-COF-OMe and 3D-TPB-COF-Ph), through the polycondensation of tetra­(p-aminophenyl)­methane and methoxy- or phenyl- substituted 1,2,4,5-tetrakis­(4-formylphenyl)­benzene on the 3- and 6-positions. Amazingly, by using the continuous rotation electron diffraction technique, 3D-TPB-COF-OMe is determined to have a 5-fold interpenetrated structure with a reported pts net, while 3D-TPB-COF-Ph adopts an unprecedented self-penetrated ljh topology (ljh = Luojia Hill) that does not exist in the database of ToposPro. Therefore, by altering the substituents from methoxy to phenyl groups, the topology of designed 3D COFs changes accordingly, and a rare net is now available. This result clearly demonstrates that such COF structures need to be carefully determined due to its complexity, and moreover, it is promising to design 3D COFs with new topology for interesting application by increasing the steric hindrance of molecular building blocks.

Substoichiometric 3D Covalent Organic Frameworks Based on Hexagonal Linkers

“…To date, studies are mainly devoted to 2D structures, and research on 3D COFs is rather less developed. Many obstacles have been well documented that limit the exploration of 3D COFs; apart from the crystallization problems, structural determination is also a bothersome issue. ,, Here in this work, we show that partially connected covalencies also exist in 3D COFs, which is an exciting finding not yet uncovered in COFs. It is further demonstrated that the residual benzaldehydes persevered in COF frameworks can sterically regulate the interpenetration number within a 3D structure, while facilitating the effective gas adsorption and separation for 2D examples.…”

Reticular design and crystal structure determination of covalent organic frameworks

“…Very recently, by using a similar strategy, Sun and Wang et al reported topology control in 3D COFs. 52 In particular, by tuning the geometry of building units using steric hindrance, 3D COFs including 5-fold interpenetrated pts (methoxy was introduced on the square unit) and 2-fold interpenetrated ljh (phenyl was substituted on the square unit) were obtained.…”

A Cubic 3D Covalent Organic Framework with nbo Topology

“…Such polyhedron-shaped building units may be prefabricated and then linked together to form COFs. COFs with dia , lon , bor , ctn , pts and ljh topologies have been realized using tetrahedral units, while acs , stp or ceq COFs use trigonal prism units, and pcu or soc COFs use octahedral units. The synthesis of polyhedral organic building blocks can be challenging, however, which adds complexity to this route.…”