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 (NH4+) 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 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 center dot NH4 center dot DMF preserves the pore architecture and open polar oxygen sites, exhibiting remarkably selective sorption of CO2 (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).

Automated summary

This study presents a new approach of using inorganic ammonium cations as hydrogen bond donors to regulate the assembly of carboxylic tectons and build robust hydrogen-bonded frameworks. The resulting frameworks exhibit permanent ultra-micropores and open oxygen sites, with diverse pore architectures achieved by bridging different building blocks with tetrahedral NH4+. The activated porous PTBA·NH4·DMF demonstrates remarkable selective sorption of CO2 over N2 and H2.