Ionothermal Synthesis of Imide‐Linked Covalent Organic Frameworks

Abstract

Covalent organic frameworks (COFs) are an extensively studied class of porous materials, which distinguish themselves from other porous polymers in their crystallinity and high degree of modularity, enabling a wide range of applications. COFs are most commonly synthesized solvothermally, which is often a time‐consuming process and restricted to well‐soluble precursor molecules. Synthesis of polyimide‐linked COFs (PI‐COFs) is further complicated by the poor reversibility of the ring‐closing reaction under solvothermal conditions. Herein, we report the ionothermal synthesis of crystalline and porous PI‐COFs in zinc chloride and eutectic salt mixtures. This synthesis does not require soluble precursors and the reaction time is significantly reduced as compared to standard solvothermal synthesis methods. In addition to applying the synthesis to previously reported imide COFs, a new perylene‐based COF was also synthesized, which could not be obtained by the classical solvothermal route. In situ high‐temperature XRPD analysis hints to the formation of precursor–salt adducts as crystalline intermediates, which then react with each other to form the COF.

Cyclotetrabenzil-Based Porous Organic Polymers with High Carbon Dioxide Affinity

“…Inspired by these results, we targeted the synthesis of a macrocycle-containing 3D POP, 3D-mPOP, by reacting octaketone with 1,2,4,5-tetraaminobenzene under ionothermal conditions using a ZnCl2/KCl/NaCl eutectic salt mixture (Scheme 1c) at 250 °C. 16 Since the eutectic salt mixture has a lower melting point than ZnCl2, it enables the polymerization reaction to proceed at lower temperatures, which is critical to avoid partial carbonization. The formation of 3D-mPOP was verified by Fourier-Transform Infrared (FTIR) and X-ray Photoelectron Spectroscopy (XPS) analyses (Figure 1a-b).…”

Solving the COF trilemma: towards crystalline, stable and functional covalent organic frameworks

“…47 Recently, a new synthetic route to imide COFs has been reported based on ionothermal synthesis using ZnCl 2 or eutectic salt mixtures. 5 2.2.3. Enhancing reversibility.…”

“…Crystallinity is also central to characterizing COFs, which is usually done by powder X-ray diffraction (PXRD) in combination with structure modelling and Pawley or Rietveld refinement, or very rarely by single crystal diffraction. 4 Even for characterization techniques that do not rely on crystallinity such as solid-state NMR, a reduced line width in highly crystalline materials can improve the information that can be extracted from the measurements, 5 thereby allowing for a better understanding and prediction of properties.…”

Conquering the crystallinity conundrum: efforts to increase quality of covalent organic frameworks

“…42 Recently, an easier method was developed using ZnCl 2 , as already routinely done in CTF synthesis, 141 taking only 48 hours to crystallize the COF. 185 To form Pi-COF-3 or TAPB-PTCDA COF, both linkers were combined with anhydrous ZnCl 2 and reacted under vacuum for 48 h at 300 1C, as shown in Fig. 21.…”