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]_n·DMF, TMU-34(-2H), [Zn(OBA)(DPT)_0.5]_n·DMF, and TMU-5, [Zn(OBA)(BPDH)_0.5]_n·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 Q_st(CH₄) for TMU-5, TMU-34, and TMU-34(-2H) are 27, 23, and 22 kJ mol^-1, respectively. These Q_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.