Microporous Metal−Organic Frameworks Incorporating 1,4-Benzeneditetrazolate: Syntheses, Structures, and Hydrogen Storage Properties

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Abstract
The potential of tetrazolate-based ligands for forming metal−organic frameworks of utility in hydrogen storage is demonstrated with the use of 1,4-benzeneditetrazolate (BDT2-) to generate a series of robust, microporous materials. Reaction of H2BDT with MnCl2·4H2O and Mn(NO3)2·4H2O in N,N-diethylformamide (DEF) produces the two-dimensional framework solids Mn3(BDT)2Cl2(DEF)6 (1) and Mn4(BDT)3(NO3)2(DEF)6 (2), whereas reactions with hydrated salts of Mn2+, Cu2+, and Zn2+ in a mixture of methanol and DMF afford the porous, three-dimensional framework solids Zn3(BDT)3(DMF)4(H2O)2·3.5CH3OH (3), Mn3(BDT)3(DMF)4(H2O)2·3CH3OH·2H2O·DMF (4), Mn2(BDT)Cl2(DMF)2·1.5CH3OH·H2O (5), and Cu(BDT)(DMF)·CH3OH·0.25DMF (6). It is shown that the method for desolvating such compounds can dramatically influence the ensuing gas sorption properties. When subjected to a mild evacuation procedure, compounds 3−6 exhibit permanent porosity, with BET surface areas in the range 200−640 m2/g. The desolvated forms of 3−5 store between 0.82 and 1.46 wt % H2 at 77 K and 1 atm, with enthalpies of adsorption in the range 6.0−8.8 kJ/mol, among the highest so far reported for metal−organic frameworks. In addition, the desolvated form of 6 exhibits preferential adsorption of O2 over H2 and N2, showing promise for gas separation and purification applications.

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