Two proton-conductive metal-organic frameworks constructed by pyridyl imidazole dicarboxylate ligands

Abstract

To explore the proton conduction in more MOFs bearing N-heterocyclic carboxylate, herein, a 1-D metal-organic framework (MOF), [Mn(3-HPyIDC)(H2O)2]n (1) (3-H3PyIDC = 2-(3-pyridyl)-4,5-imidazole dicarboxylic acid) and a 3-D MOF, [Cd(4-HPyIDC)(H2O)]n (2) (4-H3PyIDC = 2-(4-pyridyl)-4,5-imidazole dicarboxylic acid) were successfully prepared. Their excellent thermal and water stability was verified across thermogravimetric and powder X-ray diffraction determinations. The AC impedance test shows that their proton conductivity boosts with increasing temperatures and humidities, and the optimal value can be above 10−4 S/cm. The frameworks containing a large number of free carboxyl groups or coordination H2O units together with the H-bonded networks are very conducive to proton transfer. Their proton-conducting mechanisms were further investigated in light of the calculated values of activation energies.