High Proton Conductivity in a Flexible, Cross-Linked, Ultramicroporous Magnesium Tetraphosphonate Hybrid Framework

Multifunctional materials, especially those combining two or more properties of interest, are attracting immense attention due to their potential applications. MOFs, metal organic frameworks, can be regarded as multifunctional materials if they show another useful property in addition to the adsorption behavior. Here, we report a new multifunctional light hybrid, MgH6ODTMP center dot 2H(2)O(DMF)(0.5) (1), which has been synthesized using the tetraphosphonic acid H8ODTMP, octamethylenediamine-N,N,N',N'-tetralds(methylenephosphonic acid), by high-throughput methodology. Its crystal structure, solved by Patterson-function direct methods from synchrotron powder Xray diffraction, was characterized by a 3D pillared open framework containing cross-linked ID channels filled with water and DMF. Upon H2O and DMF removal and subsequent rehydration, MgH6ODTMP center dot 2H(2)O (2) and MgH6ODTMP center dot 6H(2)O (3) can be formed. These processes take place through crystalline-quasi-amorphous-crystalline transformations, during which the integrity of the framework is maintained. A water adsorption study, at constant temperature, showed that this magnesium tetraphosphonate hybrid reversibly equilibrates its lattice water content as a function of the water partial pressure. Combination of the structural study and gas adsorption characterization (N-2, CO2, and CH4) indicates an ultramicroporous framework. High-pressure CO2, adsorption data are also reported. Finally, impedance data indicates that 3 has high proton conductivity sigma = 1.6 x 10(-3) S cm(-1) at T = 292 K at similar to 100% relative humidity with an activation energy of 0.31 eV.