Isomeric Scandium–Organic Frameworks with High Hydrolytic Stability and Selective Adsorption of Acetylene

Two solvent-controlled topological isomers of scandium–organic frameworks [Sc(Hpzc)(pzc)]·DMF·2H2O (1·DMF·2H2O) and [Sc(Hpzc)(pzc)]·DMA·4H2O (2·DMA·4H2O) were synthesized using 2,5-pyrazinedicarboxylate (pzc2–) (DMF = dimethylformamide; DMA = dimethylacetamide). Despite the isomeric nature of the obtained metal–organic frameworks (MOFs), they possess different structural features and unique adsorption properties toward gases and iodine. The compound 1 has widely spread among MOF structures a dia topology with ultranarrow channels, which together with inner surface functionalization leads to enhanced CO2 adsorption and high selectivity factors in CO2/CH4 and CO2/N2 gas mixtures (25.9 and 35.6, respectively, 1/1 v/v). Moreover, a rare preferable adsorption of CO2 over C2H2 was demonstrated. The biporous isomeric framework 2 has a crb topology inherent in zeolites. A remarkable adsorption affinity to C2H2 with the ideal adsorbed solution theory selectivity factor of 127.1 for a C2H2/C2H4 mixture (1/99 v/v) was achieved for 2. Both compounds have exceptional chemical stability in a wide range of pH from acidic to basic media.