Structural Isomerism and Effect of Fluorination on Gas Adsorption in Copper-Tetrazolate Based Metal Organic Frameworks

Abstract

Synthesis, structure, and gas adsorption properties of three Metal Organic Frameworks (MOFs) synthesized from predesigned ligands 4-(1H-tetrazole-5-yl)benzoic acid (4-TBA) and 2-fluoro-4-(1H-tetrazole-5-yl)benzoic acid (2F-4-TBA) along with Cu(II) as an metal precursor has been reported. Among these MOFs, Cu9(4-TBA)10(C2H5OH)2 (Cu-TBA-1) and Cu2(4-TBA)2(DMF)(C2H5OH) (Cu-TBA-2) are structural isomers. Whereas, Cu2(4-TBA)2(DMF)(C2H5OH) (Cu-TBA-2) and Cu2(2-F-4-TBA)2(DMF)2 (Cu-TBA-2F) have similar crystal structure. N2 adsorption isotherms of the activated sample of Cu-TBA-1 and -2 exhibit types-I sorption behavior with a Langmuir and Brunauer–Emmett–Teller (BET) surface area of 686, 402 m2/g and 616, 356 m2/g, respectively. It is noteworthy that Cu-TBA-1 and -2 adsorbs 1.16 and, 1.54 wt % H2, while Cu-TBA-2F adsorbs 0.67 wt % at 77 K and 1 atm. On the other hand, Cu-TBA-1 and -2 adsorb 3.08 and 2.54 mmol/g, while Cu-TBA-2F adsorbs 1.27 mmol/g of CO2 at 298 K and 1 bar pressure. H2 adsorption sites in Cu-TBA-2 and -2F have been analyzed by molecular simulation.