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.