Balancing Porosity and Binding Affinity in Vinyl-Functionalized Zr-Based Metal-Organic Frameworks for Gas Adsorption

Gas storage and capture in metal-organic frameworks (MOFs) are significantly influenced by the interplay between porosity and specific binding sites. In particular, a critical challenge in adsorbent design is the loss of porosity that often accompanies the incorporation of strong interaction sites. Herein, we demonstrate a systematic study on how a vinyl functional group embedded within organic struts with different lengths modulates gas-framework interactions. We investigate two isostructural Zr-based MOFs, Zr-CVB [Zr₆O₄(OH)₄(CVB)₆] (H₂CVB = 4-(2-carboxyvinyl)benzoic acid) and Zr-CVN [Zr₆O₄(OH)₄(CVN)₆] (H₂CVN = (E)-6-(2-carboxyvinyl)-2-naphthoic acid), using UiO-67 as a benchmark. The integration of the vinyl moiety in Zr-CVN and Zr-CVB clearly improved the isosteric heats of adsorption (Q_st) for H₂ (9.4 kJ mol^-1 for Zr-CVN and 11.2 kJ mol^-1 for Zr-CVB) and CO₂ (24.8 kJ mol^-1 for Zr-CVN and 34.2 kJ mol^-1 for Zr-CVB), which are attributed to the H-π and quadrupole-π interactions, respectively. These Q_st values represent the highest reported values among Zr-based MOFs with comparable surface areas. This behavior deviates from the conventional trade-off between surface area (S_BET) and isosteric heats (Q_st) observed in Zr-based MOFs. These results establish a backbone-embedded vinyl functionality as an effective structural design strategy for enhancing gas adsorption without compromising porosity.