Carbon Dioxide Capture and Utilization with Isomeric Forms of Bis(amino)‐Tagged Zinc Bipyrazolate Metal–Organic Frameworks

Aiming at extending the tagged zinc bipyrazolate metal–organic frameworks (MOFs) family, the ligand 3,3’‐diamino‐4,4’‐bipyrazole ( 3,3’‐H 2 L ) has been synthesized in good yield. The reaction with zinc(II) acetate hydrate led to the related MOF Zn(3,3’‐L) . The compound is isostructural with its mono(amino) analogue Zn(BPZNH 2 ) and with Zn(3,5‐L) , its isomeric parent built with 3,5‐diamino‐4,4’‐bipyrazole. The textural analysis has unveiled its micro‐/mesoporous nature, with a BET area of 463 m 2  g −1 . Its CO 2 adsorption capacity (17.4 wt. % CO 2 at p CO2 = 1 bar and T = 298 K) and isosteric heat of adsorption ( Q st = 24.8 kJ mol −1 ) are comparable to that of Zn(3,5‐L) . Both Zn(3,3’‐L) and Zn(3,5‐L) have been tested as heterogeneous catalysts in the reaction of CO 2 with the epoxides epichlorohydrin and epibromohydrin to give the corresponding cyclic carbonates at T = 393 K and p CO2 = 5 bar under solvent‐ and co‐catalyst‐free conditions. In general, the conversions recorded are higher than those found for Zn(BPZNH 2 ), proving that the insertion of an extra amino tag in the pores is beneficial for the epoxidation catalysis. The best catalytic match has been observed for the Zn(3,5‐L) /epichlorohydrin couple, with 64 % conversion and a TOF of 5.3 mmol(carbonate) (mmol Zn ) −1  h −1 . To gain better insights on the MOF‐epoxide interaction, the crystal structure of the [epibromohydrin@ Zn(3,3’‐L) ] adduct has been solved, confirming the existence of Br⋅⋅⋅(H)−N non‐bonding interactions. To our knowledge, this study represents the first structural determination of a [epibromohydrin@MOF] adduct.