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 Qst(CH4) for TMU-5, TMU-34, and TMU-34­(−2H) are 27, 23, and 22 kJ mol–1, respectively. These Qst 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.