High Proton Conduction in Two Highly Water-Stable Lanthanide Coordination Polymers from a Triazole Multicarboxylate Ligand.

Two lanthanide coordination polymers (CPs) {[Er(Hmtbd)(Hmtbd)(HO)]·2HO} () and [Yb(Hmtbd)(Hmtbd)(HO)] () carrying an N-heterocyclic carboxylate ligand 5-(3-methylformate-1-1,2,4-triazole-1-methyl)benzen-1,3-dicarboxylate (Hmtbd) were prepared under solvothermal conditions. The single-crystal X-ray diffraction data demonstrate that and are isostructural and display 1D chain structure. Alternating current (AC) impedance measurements illustrate that the highest proton conductivities of and can attain 5.09 × 10 and 3.09 × 10 S·cm at 100 °C and 98% relative humidity (RH), respectively. The value of exceeds those of most reported lanthanide-based crystalline materials and ranks second among the described Er-CPs under similar conditions, whereas the value for is the highest proton conductivity among the previous Yb-CPs. Coupled with the structural analyses of the two CPs and HO vapor adsorption, the calculated values help to deduce their proton conductive mechanisms. Notably, the N-heterocyclic units (triazole), carboxyl, and hydrogen-bonding network all play key roles in the proton-transfer process. The prominent proton conductive abilities of both CPs show great promise as efficient proton conductors.