In situ monitoring of mechanochemical covalent organic framework formation reveals templating effect of liquid additive

Abstract

Covalent organic frameworks (COFs) have emerged as a new class of molecularly precise, porous functional materials characterized by a broad structural and chemical versatility, leading to a diverse range of applications. Despite the increasing popularity of COFs, fundamental aspects of their formation are poorly understood and profound experimental insights into their formation processes are still lacking.Here we use a combination of in situ X-ray powder diffraction and Raman spectroscopy to elucidate the reaction mechanism of mechanochemically synthesized imine COFs, leading to the observation of key reaction intermediates. Real-time monitoring provides experimental evidence of templating effects by the liquid additive for the subsequent pore formation and layer assembly. Moreover, the solid-state catalyst scandium triflate Sc(OTf)3 is revealed to be instrumental in directing the reaction kinetics and mechanism, resulting in products with crystallinity and porosity en par with solvothermally synthesized COFs. This work highlights the potential of mechanochemistry as a green synthetic route towards COF synthesis, and emphasizes the subtle interplay between choice of liquid additives, catalysts, and activation procedure.

Identifying the roles of imine and alkyne linkages in determining the photocatalytic hydrogen evolution over thiadiazole-based covalent organic frameworks

“…Further analysis of the structure and chemical composition of the as-prepared COFs was performed using Fourier transform infrared (FTIR) and solid-state 13 C NMR spectroscopy. 33 As shown in Fig. 2d, both COFs exhibit similar IR bands with a peak centered at 1578 and 1506 cm −1 , which could be ascribed to the CN and CC, stretching the two monomers.…”

Synthesis of Boroxine and Dioxaborole Covalent Organic Frameworks via Transesterification and Metathesis of Pinacol Boronates

“…The kinetic analysis of COF formation is important for the understanding of the growth mechanism and reaction optimization toward improved COF crystallinity/order. − However, analyzing the kinetics of heterogeneous polymerization is a challenge, and only recently, the experimental measurements of the kinetic of COF formation have been reported using X-ray scattering, , turbidity, , and PXRD/Raman spectroscopy . Each of these techniques possesses its unique advantages and limitations, but none have the generality/resolution of liquid NMR, as commonly employed in measuring the rate of bond formation in solution chemistry.…”

“…27−32 However, analyzing the kinetics of heterogeneous polymerization is a challenge, and only recently, the experimental measurements of the kinetic of COF formation have been reported using X-ray scattering, 32,33 turbidity, 34,35 and PXRD/ Raman spectroscopy. 36 Each of these techniques possesses its unique advantages and limitations, but none have the generality/resolution of liquid NMR, as commonly employed in measuring the rate of bond formation in solution chemistry. Since both the reactants and the byproduct (MBpin) are soluble and thus quantifiable by NMR, our metathesis polymerization allows for an easy kinetic study of polymerization.…”

Time‐Resolved In Situ Monitoring of Mechanochemical Reactions

“…Many TRIS studies indicate that control over the polymorphic outcome of a milling experiment can be obtained through careful choice of the liquid additive in LAG reactions [50, 106] . In these examples, the polarity of the solvents used has a decisive influence, whereas in other cases the solvent can also act as a template [107, 108] . The templating effect of solvent molecules for the mechanochemical synthesis of covalent organic frameworks (COFs) was identified on the basis of TRIS‐XRD data [108] .…”