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

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 m2 g–1. 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 (c) hydrogen bonding between the terminal heteroaromatic rings.

https://pubs.acs.org/doi/abs/10.1021/jacs.8b02869

Mohamed I. HashimHa T. M. LeTeng-Hao ChenYu-Sheng ChenOlafs Daugulis , Chia-Wei HsuAllan J. Jacobson†§Watchareeya Kaveevivitchai#Xiao LiangTatyana MakarenkoOgnjen Š. Miljanić* , Ilja PopovsHung Vu TranXiqu WangChia-Hua Wu, and Judy I. Wu 

 Department of Chemistry, University of Houston, 3585 Cullen Boulevard #112, Houston, Texas 77204-5003, United States

 Center for Advanced Radiation Source (ChemMatCARS), The University of Chicago, c/o APS/ANL, 9700 South Cass Drive, Argonne, Illinois 60439, United States

§ Texas Center for Superconductivity, 202 UH Science Center, Houston, Texas 77204-5002, United States

Adapted with permission from J. Am. Chem. Soc., 2018, 140 (18), pp 6014–6026. Copyright 2018 American Chemical Society.