Construction of structural diversity and fine-tuned porosity in acylamide MOFs by a synthetic approach†
Abstract
Four new metal–organic frameworks (MOFs), namely, Zn(L1)(AzDC)·(DMF)3 (1), Zn(L2) (AzDC)·(DMF)0.5(H2O) (2), Zn2(AzDC)2(L3)·(DMF)(H2O)0.5 (3), and Zn(AzDC)(L3)·(DMF) (4), (L1 = N1,N4-di(pyridin-4-yl)terephthalamide, L2 = N1,N4-di(pyridin-3-yl)terephthalamide, L3 = N4,N4′-di(pyridin-4-yl)-[1,1′-biphenyl]-4,4′-dicarboxamide, H2AzDC = 4,4′-(diazene-1,2-diyl)dibenzoic acid, DMF = N,N-dimethylformamide) were prepared by the solvothermal reaction of Zn(NO3)2, H2AzDC, and acylamide ligands. Polymers 1–3 show the common layer-pillared pcu-type net with four- or two-fold interpenetration, while polymer 4 displays an unprecedented four-connected net with the 638210 topology symbol. Note that the difference in the pillar of L1 for 1 and L2 for 2, related to the position isomers, caused significant alterations, including a reduction in the interpenetration number from four to two, enhanced potential porosity from 47.1% to 66.6%, and a change in the pore configuration from a smaller triangle window to a larger quadrangle window. Furthermore, controlling the volume of the reaction solvent, such as 5 mL for 3 and 15 mL for 4, also resulted in significant alterations, including a change in the structural diversity from a four-fold interpenetrating pcu net to a two-fold interpenetrating 638210 net, enhanced potential porosity from 49.1% to 57.2%, and a change in the pore configuration from a smaller rectangle window to a larger quadrangle window. Most importantly, all these polymers display highly selective adsorption of CO2 over other gases, such as N2, CH4, CO, and O2, most likely due to the free standing acylamide groups the polymers contain, which afford unique affinity towards CO2.