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High Proton Conductivity by a Metal–Organic Framework Incorporating Zn8O Clusters with Aligned Imidazolium Groups Decorating the Channels

Sen, Susan, Nair, Nisanth N., Yamada, Teppei, Kitagawa, Hiroshi, Bharadwaj, Parimal K.
Journal of the American Chemical Society 2012 v.134 no.47 pp. 19432-19437
X-ray diffraction, activation energy, fuel cells, heat, ligands, solvents
A novel metal–organic framework, [{(Zn₀.₂₅)₈(O)}Zn₆(L)₁₂(H₂O)₂₉(DMF)₆₉(NO₃)₂]ₙ (1) {H₂L = 1,3-bis(4-carboxyphenyl)imidazolium}, has been synthesized under solvothermal conditions in good yield. It shows a Zn₈O cluster that is coordinated to six ligands and forms an overall three-dimensional structure with channels along the crystallographic a and b axes. The imidazolium groups of the ligand moiety are aligned in the channels. The channels are not empty but are occupied by a large number of DMF and water molecules. Upon heating, these solvent molecules can be removed without breakdown of the overall structure of the framework as shown by variable-temperature powder X-ray diffraction patterns. Of great interest is the fact that the compound exhibits high proton conductivity with a low activation energy that is comparable to those of Nafion presently used in fuel cells.