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Probe metal binding mode of imine covalent organic frameworks: cycloiridation for (photo)catalytic hydrogen evolution from formate.

ABSTRACT: Metalation of covalent organic frameworks (COFs) is a critical strategy to functionalize COFs for advanced applications yet largely relies on the pre-installed specific metal docking sites in the network, such as porphyrin, salen, 2,2'-bipyridine, etc. We show in this study that the imine linkage of simple imine-based COFs, one of the most popular COFs, readily chelate transition metal (Ir in this work) via cyclometalation, which has not been explored before. The iridacycle decorated COF exhibited more than 10-fold efficiency enhancement in (photo)catalytic hydrogen evolution from aqueous formate solution than its molecular counterpart under mild conditions. This work will inspire more functional cyclometallated COFs to be explored beyond catalysis considering the large imine COF library and the rich metallacycle chemistry.

SUBMITTER: Hu J

PROVIDER: S-EPMC8188469 | biostudies-literature | 2021 May

REPOSITORIES: biostudies-literature

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Probe metal binding mode of imine covalent organic frameworks: cycloiridation for (photo)catalytic hydrogen evolution from formate.

Hu Jiyun J Mehrabi Hamed H Meng Yin-Shan YS Taylor Maddison M Zhan Jin-Hui JH Yan Qigeng Q Benamara Mourad M Coridan Robert H RH Beyzavi Hudson H

Chemical science 20210511 22

Metalation of covalent organic frameworks (COFs) is a critical strategy to functionalize COFs for advanced applications yet largely relies on the pre-installed specific metal docking sites in the network, such as porphyrin, salen, 2,2'-bipyridine, <i>etc.</i> We show in this study that the imine linkage of simple imine-based COFs, one of the most popular COFs, readily chelate transition metal (Ir in this work) <i>via</i> cyclometalation, which has not been explored before. The iridacycle decorat ...[more]

PMID: 34168847

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Project description:Mechanistic understanding into the formation and growth of imine-linked two-dimensional (2D) covalent organic frameworks (COFs) is needed to improve their materials quality and access larger crystallite sizes, both of which limit the promise of 2D COFs and 2D polymerization techniques. Here we report a previously unknown temperature-dependent depolymerization of colloidal 2D imine-linked COFs, which offers a new means to improve their crystallinity. 2D COF colloids form at room temperature but then depolymerize when their reaction mixtures are heated to 90 °C. As the solutions are cooled back to room temperature, the 2D COFs repolymerize and crystallize with improved crystallinity and porosity, as characterized by X-ray diffraction, infrared spectroscopy and N2 porosimetry. The evolution of COF crystallinity during the solvothermal depolymerization and repolymerization processes was characterized by in situ wide angle X-ray scattering, and the concentrations of free COF monomers as a function of temperature were quantified by variable temperature 1H NMR spectroscopy. The ability of a 2D COF to depolymerize under these conditions depends on both the identity of the COF and its initial materials quality. For one network formed at room temperature (TAPB-PDA COF), a first depolymerization process is nearly complete, and the repolymerization yields materials with dramatically enhanced crystallinity and surface area. Already recrystallized materials partially depolymerize upon heating their reaction mixtures a second time. A related 2D COF (TAPB-DMTA COF) forms initially with improved crystallinity compared to TAPB-PDA COF and then partially depolymerizes upon heating. These results suggest that both high materials quality and network-dependent properties, such as interlayer interaction strength, influence the extent to which 2D COFs resist depolymerization. These findings offer a new means to recrystallize or solvent anneal 2D COFs and may ultimately inform crystallization conditions for obtaining large-area imine-linked two-dimensional polymers from solution.

Dataset Information

Probe metal binding mode of imine covalent organic frameworks: cycloiridation for (photo)catalytic hydrogen evolution from formate.

Publications

Probe metal binding mode of imine covalent organic frameworks: cycloiridation for (photo)catalytic hydrogen evolution from formate.

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