Charge-Assisted Hydrogen-Bonded Organic Frameworks with Inorganic Ammonium Regulated Switchable Open Polar Sites.

Surface open polar sites within the voids of porous molecular crystals define the localized physicochemical environment for critical functions such as gas separation and molecular recognition. This study presents a new charge-assisted hydrogen bonding (H-bonding) motif, by exploiting inorganic ammonium (NH 4 + ) cations as H-bond donors, to regulate the assembly of C 2 -symmetric carboxylic tectons for building robust H-bonded frameworks with permanent ultra-micropores and open oxygen sites. Diverse building blocks are bridged by tetrahedral NH 4 + to expand distinctive H-bonded networks with varied pore architectures. Particularly, the open polar oxygen sites can be switched by altering NH 4 + sources to tune the deprotonation of carboxyl-containing tectons. The activated porous PTBA·NH 4 ·DMF preserves the pore architecture and open polar oxygen sites, exhibiting remarkably selective sorption of CO 2 (107.8 cm 3 g -1 ,195 K) over N 2 (11.2 cm 3 g -1 , 77 K) and H 2 (1.4 cm 3 g -1 , 77 K).