Dissecting Porosity in Molecular Crystals: Influence of Geometry, Hydrogen Bonding, and [π···π] Stacking on the Solid-State Packing of Fluorinated Aromatics

Abstract

Porous molecular crystals are an emerging class of porous materials that is unique in being built from discrete molecules rather than being polymeric in nature. In this study, we examined the effects of molecular structure of the precursors on the formation of porous solid-state structures with a series of 16 rigid aromatics. The majority of these precursors possess pyrazole groups capable of hydrogen bonding, as well as electron-rich aromatics and electron-poor tetrafluorobenzene rings. These precursors were prepared using a combination of Pd- and Cu-catalyzed cross-couplings, careful manipulations of protecting groups on the nitrogen atoms, and solvothermal syntheses. Our study varied the geometry and dimensions of precursors, as well as the presence of groups capable of hydrogen bonding and [π···π] stacking. Thirteen derivatives were crystallographically characterized, and four of them were found to be porous with surface areas between 283 and 1821 m g. Common to these four porous structures were (a) rigid trigonal geometry, (b) [π···π] stacking of electron-poor tetrafluorobenzenes with electron-rich pyrazoles or tetrazoles, and

Water‐Assisted Emission Enhancement of 2‐Hydroxynaphthaldoxime and Related Compounds

“…The proton b originally appeared as a doublet at 8.48 ppm shifted to 8.08 ppm. A tilt of a slip π⋅⋅⋅π stack structure is expected to cause chemical shift of C−H protons of stacking rings by changing the position of signal to a high‐shielding position. Such shifts are common in the stacking of DNA based molecules .…”

Docking Strategy To Construct Thermostable, Single‐Crystalline, Hydrogen‐Bonded Organic Framework with High Surface Area

“…However, such reversibility and the weakness of H‐bonds frequently cause the collapse of the frameworks after removal of the solvent molecules from the pores, so there is a lack of a universal design strategy for HOFs. To resolve these problems, well‐designed supramolecular synthons have been applied, such as benzimidasolone, pyrazole,, and the 2,4‐diaminotriazinyl group, as well as dimerization through carboxy groups, which is the most classic and simplest supramolecular synthon…”

“…However, it remains a challenge to obtain sophisticated HOFs with precise crystal structures, large permanent pores, and both chemical and thermal stability. Only a handful of HOFs have been reported with both upper temperature limits of over 200 °C and Brunauer–Emmett–Teller (BET) surface areas [SA (BET) ] of over 1000 m 2 g −1 ; these are HOF‐TCBP reported by Wu and Yuan et al., trispyrazole derivatives reported by Miljanić et al.,, IISERP‐HOF1 reported by Vaidhyanathan et al., and HOF‐5a reported by Chen et al . A more generalized strategy is required to achieve such HOFs systematically.…”

Self-Recognizing π-π Stacking Interactions Designed for the Generation of Ultrastable Mesoporous Hydrogen-Bonded Organic Frameworks

“…Such tectons usually form 2D layers by H-bonding while cooperative π-π stacking interactions exist between 2D layers, which has proven to be a reliable approach to stabilize HOF materials. 8,11,[29][30][31][32] For example, a series of HOFs with isostructural or quasi-isostructural honeycomb frameworks has been prepared by assembling tectons with C 3 -or C 6 -symmetries. 29,33 However, as the length of tectons increases, the π-π stacking between 2D layers tends to be in a staggered manner rather than eclipsed, which leads to a decrease in the pore size of these HOFs.…”