Four Lanthanide(III) Metal-Organic Frameworks Fabricated by Bithiophene Dicarboxylate for High Inherent Proton Conduction

Currently, it is still a challenge to directly achieve highly stable metal-organic frameworks (MOFs) with superior proton conductivity solely through the exquisite design of ligands and the attentive selection of metal nodes. Inspired by this, we are intrigued by a multifunctional dicarboxylate ligand including dithiophene groups, 3,4-dimethylthieno[2,3-b]thiophene-2,5-dicarboxylic acid (H2DTD), and lanthanide ions with distinct coordination topologies. Successfully, four isostructural three-dimensional lanthanide(III)-based MOFs, [Ln(2)(DTD)(3)(DEF)(4)]center dot DEF center dot 6H(2)O [Ln(III) = Tb-III (Tb-MOF), Eu-III (Eu-MOF), Sm-III (Sm-MOF), and Dy-III (Dy-MOF)], were solvothermally prepared, in which the effective proton transport will be provided by the coordinated or free solvent molecules, the crystalline water molecules, and the framework components, as well as a large number of highly electronegative S and O atoms. As expected, the four Ln-MOFs demonstrated the highest proton conductivities (sigma) being 0.54 x 10(-3), 3.75 x 10(-3), 1.28 x 10(-3), and 1.92 x 10(-3) S center dot cm(-1) for the four MOFs, respectively, at 100 degree celsius/98% relative humidity (RH). Excitingly, Dy-MOF demonstrated an extraordinary ultrahigh sigma of 1 x 10(-3) S center dot cm(-1) at 30 degree celsius/98% RH. Additionally, the plausible proton transport mechanisms were emphasized.