phenylene (HHTP) and linear tetrafluorophthalonitrile (TFPN) or 2,3,5,6-tetrafluoro-4-pyridinecarbonitrile (TFPC) were linked by 1,4-dioxin linkages to form crystalline 2D covalent organic frameworks, termed COF-316 and-318. Unlike the condensation reactions commonly used to crystallize the great majority of COFs, the reactions used in this report are based on nucleophilic aromatic substitution reactions (S N Ar) that are considered irreversible. Our studies show that the reactivity of TFPN and TFPC with HHTP is enhanced by the nitrile substituents leading to facile reactions of planar building units to yield the present 1,4-dioxin linked COFs. Because these reactions are irreversible, the resultant frameworks have high chemical stability in both acid and base. This has led to postsynthetic modifications of COF-316 by reactions necessitating extreme conditions to covalently install functionalities not otherwise accessible. We also report the permanent porosity of these COFs.

The synthesis of a new anionic 3D metalcatecholate framework, termed MOF-1992, is achieved by l i n k i n g t e t r a t o p i c c o b a l t p h t h a l o c y a n i n-2 , 3 , 9 , 1 0 , 1 6 , 1 7 , 2 3 , 2 4-o c t a o l l i n k e r s w i t h Fe 3 (−C 2 O 2 −) 6 (OH 2) 2 trimers into an extended framework of roc topology. MOF-1992 exhibits sterically accessible Co active sites together with charge transfer properties. Cathodes based on MOF-1992 and carbon black (CB) display a high coverage of electroactive sites (270 nmol cm −2) and a high current density (−16.5 mA cm −2 ; overpotential, −0.52 V) for the CO 2 to CO reduction reaction in water (faradaic efficiency, 80%). Over the 6 h experiment, MOF-1992/CB cathodes reach turnover numbers of 5800 with turnover frequencies of 0.20 s −1 per active site.

Figure 1. (a) The 5 edge-transitive topologies for 2D COFs. (b) The 6 topologies with 3 kinds of vertices and 2 kinds of edges. Communication pubs.acs.org/JACS