Size- and shape-selective isostructural microporous metal-organic frameworks with different effective aperture sizes

Area of Science:

• Materials Science
• Chemistry
• Nanotechnology

Background:

• Metal-organic frameworks (MOFs) are crystalline porous materials with tunable structures.
• Understanding pore size and shape effects on gas adsorption is crucial for separation technologies.

Purpose of the Study:

• To synthesize isostructural MOFs with identical static aperture sizes but varying effective aperture sizes.
• To investigate the gas adsorption selectivity of these MOFs based on adsorbate shape and minimum diameter.
• To explore the role of framework flexibility in gas separation.

Main Methods:

• Synthesis of two isostructural MOFs using 5-(pyridin-3-ylethynyl)isophthalic acid ligand.
• Characterization of MOF structures and pore dimensions.
• Gas adsorption studies using N2 and Ar as probe molecules.

Main Results:

• MOFs exhibit size selectivity based on adsorbate minimum diameter, differentiating N2 and Ar.
• Cage B shows shape selectivity, admitting linear N2 but excluding spherical Ar due to pore aperture shape.
• Isostructural MOFs with same static pore size display different selectivity due to framework flexibility and effective aperture size variations.

Conclusions:

• MOFs can achieve selective gas adsorption by exploiting adsorbate minimum diameter and pore shape.
• Framework flexibility plays a significant role in determining effective pore size and gas separation performance.
• These findings offer new strategies for designing MOFs for precise gas separations.