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 (NH4 + ) cations as H-bond donors, to regulate the assembly of C2 -symmetric carboxylic tectons for building robust H-bonded frameworks with permanent ultra-micropores and open oxygen sites. Diverse building blocks are bridged by tetrahedral NH4 + to expand distinctive H-bonded networks with varied pore architectures. Particularly, the open polar oxygen sites can be switched by altering NH4 + sources to tune the deprotonation of carboxyl-containing tectons. The activated porous PTBA·NH4 ·DMF preserves the pore architecture and open polar oxygen sites, exhibiting remarkably selective sorption of CO2 (107.8 cm3 g-1 ,195 K) over N2 (11.2 cm3 g-1 , 77 K) and H2 (1.4 cm3 g-1 , 77 K).