Journal of the American Chemical Society, Vol.128, No.27, 8904-8913, 2006
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 (BDT2-) to generate a series of robust, microporous materials. Reaction of H2BDT with MnCl(2)(.)4H(2)O and Mn(NO3)(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)(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 Zn-3(BDT)(3)(DMF)(4)(H2O)(2)(.)3.5CH(3-)OH (3), Mn-3(BDT)(3)(DMF)(4)(H2O)(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.