Microporous metal-organic frameworks incorporating 1,4-benzeneditetrazolate: Syntheses, structures, and hydrogen storage properties

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 (BDT(2-)) to generate a series of robust, microporous materials. Reaction of H(2)BDT with MnCl(2)(.)4H(2)O and Mn(NO(3))(2)(.)4H(2)O in N,N-diethylformamide (DEF) produces the two-dimensional framework solids Mn(3)(BDT)(2)Cl(2)(DEF)(6) (1) and Mn(4)( BDT)(3)(NO(3))(2)(DEF)(6) (2), whereas reactions with hydrated salts of Mn(2+), Cu(2+), and Zn(2+) in a mixture of methanol and DMF afford the porous, three-dimensional framework solids Zn(3)(BDT)(3)(DMF)(4)(H(2)O)(2)(.)3.5CH(3-)OH (3), Mn(3)(BDT)(3)(DMF)(4)(H(2)O)(2)(.)3CH(3)OH(.)2H(2)O, DMF (4), Mn(2)(BDT)Cl(2)(DMF)(2)(.)1.5CH(3)OH(.)H(2)O (5), and Cu(BDT)(DMF)(.)CH(3)OH(.)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 m(2)/ g. The desolvated forms of 3-5 store between 0.82 and 1.46 wt% H(2) 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 O(2) over H(2) and N(2), showing promise for gas separation and purification applications.