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

Two lanthanide coordination polymers (CPs) {[Er(Hmtbd)(H₂mtbd)(H₂O)₃]·2H₂O} (1) and [Yb(Hmtbd)(H₂mtbd)(H₂O)₃] (2) carrying an N-heterocyclic carboxylate ligand 5-(3-methylformate-1H-1,2,4-triazole-1-methyl)benzen-1,3-dicarboxylate (H₃mtbd) were prepared under solvothermal conditions. The single-crystal X-ray diffraction data demonstrate that 1 and 2 are isostructural and display 1D chain structure. Alternating current (AC) impedance measurements illustrate that the highest proton conductivities of 1 and 2 can attain 5.09 × 10^-3 and 3.09 × 10^-3 S·cm^-1 at 100 °C and 98% relative humidity (RH), respectively. The value of 1 exceeds those of most reported lanthanide-based crystalline materials and ranks second among the described Er-CPs under similar conditions, whereas the value for 2 is the highest proton conductivity among the previous Yb-CPs. Coupled with the structural analyses of the two CPs and H₂O vapor adsorption, the calculated E_a 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.