Programming Structural Flexibility for Tunable Gas Sorption via Hydrogen Bonding in Polyoxometalate-Based Porous...

Area of Science:

• Materials Science
• Supramolecular Chemistry
• Chemical Engineering

Background:

• Porous ionic crystals (PICs) exhibit structural flexibility, leading to adaptive pore environments for gas sorption and separation.
• Examining both thermodynamic and kinetic aspects of guest sorption in PICs is crucial but rarely explored together.

Purpose of the Study:

• To systematically tune the structural flexibility of PICs using a crystal engineering approach.
• To investigate the combined thermodynamic and kinetic behaviors of guest sorption in PICs with varying flexibility.

Main Methods:

• Synthesized PICs using Anderson-type polyoxometalate (POM) anions and triol-ligand modification.
• Controlled structural flexibility by adjusting hydrogen bond formation between POMs and ionic components.
• Performed thermodynamic (isotherm analysis) and kinetic (sorption/desorption rates) studies for CO2 and CH3OH sorption.

Main Results:

• PICs with varying hydrogen bonding (0 for PIC-CH3 to 2 for PIC-NH2) showed distinct sorption behaviors despite similar porosities.
• PIC-NH2 exhibited a type-I isotherm (rigid framework, physisorption), while PIC-CH3 showed guest-induced structural transformation.
• Kinetic analysis revealed single-step sorption for PIC-NH2 and multistep kinetics (diffusion and framework expansion) for PIC-CH3.

Conclusions:

• A hydrogen-bonding-guided crystal engineering strategy enables precise control over PIC flexibility.
• This approach allows for tunable gas sorption properties in POM-based PICs by combining thermodynamic and kinetic insights.
• Demonstrated the potential of engineering PICs for selective gas separation applications.