Improvement of Methane–Framework Interaction by Controlling Pore Size and Functionality of Pillared MOFs

The rational design of functionalized porous metal–organic frameworks (MOFs) for gas adsorption applications has been applied using three spacer ligands H₂DPT (3,6-di­(pyridin-4-yl)-1,4-dihydro-1,2,4,5-tetrazine), DPT (3,6-di­(pyridin-4-yl)-1,2,4,5-tetrazine), and BPDH (2,5-bis­(4-pyridyl)-3,4-diaza-2,4-hexadiene) to synthesize TMU-34, [Zn­(OBA)­(H₂DPT)_0.5]_<i>n</i>·DMF, TMU-34­(−2H), [Zn­(OBA)­(DPT)_0.5]_<i>n</i>·DMF, and TMU-5, [Zn­(OBA)­(BPDH)_0.5]_<i>n</i>·1.5DMF, respectively. By controlling the pore size and chemical functionality of these three MOFs, we can improve the interactions between CO₂ and especially CH₄ with the frameworks. Calculated <i>Q</i>_st(CH₄) for TMU-5, TMU-34, and TMU-34­(−2H) are 27, 23, and 22 kJ mol^–1, respectively. These <i>Q</i>_st values are among the highest for CH₄–framework interactions. For systematic comparison, two reported frameworks, TMU-4 and TMU-5, have been compared with TMU-34 and TMU-34­(−2H) in CO₂ adsorption