A tetraaldehyde-derived porous organic cage and covalent organic frameworks: Syntheses, structures, and iodine vapor capture

Dynamic covalent imine reactions between 2′,3′-dimethoxy-[1,1′:4′,1′'-terphenyl]-3,3′',5,5′'-tetracarbaldehyde (DMTT) and cyclohexanediamine, p-phenylenediamine, and benzidine, respectively, generate a porous organic cage (DMPOC) and two covalent organic frameworks (COFs), USTB-29, and USTB-30. DMPOC shows a [3 + 6] topological cage-like structure according to single crystal X-ray diffraction result. In contrast, both microcrystalline USTB-29 and USTB-30 exhibit two-dimensional monoporous structures in an eclipsed AA stacking style based on powder X-ray diffraction and theoretical simulations. In addition, DMPOC is capable of efficiently absorbing the iodine vapor with an outstanding uptake of 5.10 g/g, much higher than that of USTB-29 (3.07 g/g) and USTB-30 (3.16 g/g). Cage to COFs transformations have been realized from DMPOC to USTB-29 and USTB-30 via the imine bond exchange with slightly increased iodine vapor uptake. Mechanism investigations uncover that both nitrogen and oxygen atoms of POC and COFs contribute to iodine vapor capture due to the formation of charge transfer matter, and loose interaction introducing adaptive expanding voids of DMPOC is suggested to capture more iodine vapor than that of COFs with strong π-π interactions.