Three isoreticular ssa-type MOFs derived from bent diisophthalate ligands: exploring the substituent effect on structural stabilities and selective C2H2/CH4 and CO2/CH4 adsorption properties

Evaluating the effect of the substituents on structural stabilities and gas adsorption properties of MOFs is fundamentally important for rational design and synthesis of new MOFs with better performance. For this purpose, three isoreticular copper-based MOFs (ZJNU-87, ZJNU-88 and ZJNU-89) with ssa-type topology were successfully constructed from bent diisophthalate ligands bearing different substituents. Permanent porosity studies reveal that the substituent has a significant effect on framework stabilities against desolvation. Utilizing nonpolar n-hexane as an activation solvent can give more optimized permanent porosity for nonpolar or less-polar substituent-modified ZJNU-88 and ZJNU-89. Furthermore, their gas adsorption properties with respect to C2H2, CO2 and CH4 were systematically investigated, revealing their promising potential for selective C2H2/CH4 and CO2/CH4 separations. In particular, methoxy-modified ZJNU-89 performs better than the methyl-modified ZJNU-88 in terms of uptake capacity and adsorption selectivity, which might be attributed to more suitable pore space of ZJNU-89.