Topochemical conversion of an imine- into a thiazole-linked covalent organic framework enabling real structure analysis

Abstract

Stabilization of covalent organic frameworks (COFs) by post-synthetic locking strategies is a powerful tool to push the limits of COF utilization, which are imposed by the reversible COF linkage. Here we introduce a sulfur-assisted chemical conversion of a two-dimensional imine-linked COF into a thiazole-linked COF, with full retention of crystallinity and porosity. This post-synthetic modification entails significantly enhanced chemical and electron beam stability, enabling investigation of the real framework structure at a high level of detail. An in-depth study by electron diffraction and transmission electron microscopy reveals a myriad of previously unknown or unverified structural features such as grain boundaries and edge dislocations, which are likely generic to the in-plane structure of 2D COFs. The visualization of such real structural features is key to understand, design and control structure–property relationships in COFs, which can have major implications for adsorption, catalytic, and transport properties of such crystalline porous polymers.

Covalent Organic Frameworks: Chemical Approaches to Designer Structures and Built‐In Functions

“…Nonconjugated COFs have been designed using boronate ester, boroxine, borosilicate, borazine, imide, amide, amine, and dioxin linkages (Figure a). The partially π‐conjugated skeletons have been constructed using hydrazone, triazine, imine, squaraine, azine, thiazole, oxazole, azodioxide, and viologen linkages (Figure b). The fully π‐conjugated skeletons have been generated with phenazine and C=C linkages (Figure c).…”

Tailoring Covalent Organic Frameworks To Capture Water Contaminants

“… Post‐synthetic modification of imine‐based COFs via chemical conversion to a) amide, b) thiazole, and c) azole linkages …”

“…Lotsch and co‐workers converted the imine moieties to thiazole using elemental sulfur (Scheme b) . No losses in crystallinity were observed after treatment with concentrated HCl, hydrazine, or NaBH 4 .…”

Kovalente organische Gerüstverbindungen: chemische Ansätze für Designerstrukturen und integrierte Funktionen

“…Nichtkonjugierte COFs sind mit Boronatester‐, Boroxin‐, Borsilicat‐, Borazin‐, Imid‐, Amid‐, Amin‐ und Dioxinverknüpfungen synthetisiert worden (Abbildung a). Teilweise π‐konjugierte Gerüste sind mit Hydrazon‐, Triazin‐, Imin‐, Squarain‐, Azin‐, Thiazol‐, Oxazol‐, Azodioxid‐ und Viologenverknüpfungen gestaltet worden (Abbildung b). Vollständig π‐konjugierte Gerüste wurden mit Phenazin‐ und C=C‐Verknüpfungen erhalten (Abbildung c).…”

“…oxazolverknüpfte COFs umgewandelt (Abbildung ) . Durch Erhitzen iminverknüpfter COFs mit Schwefel bei einer erhöhten Temperatur von 350 °C wurde die Iminverknüpfung in eine Thiazolverknüpfung umgewandelt (Abbildung ) …”