LAUSR

Finding more metal complexes with outstanding water stability and high proton conductivity still has important research significance for the energy field. Herein, two highly proton-conductive complexes, one hydrogen-bonded supramolecular framework (HSF) [Cd(CBIA)2(H2O)4]·2H2O (1) and one coordination polymer (CP), {[Cd2(CBIA)2(4,4'-bipy)2(H2O)2]·(CBIA)·(OH)·2H2O}n (2) (4,4'-bipy = 4,4'-bipyridine), were triumphantly assembled using a zwitterionic organic compound, 2-(1-(carboxymethyl)-1H-benzo[d]imidazol-3-ium-3-yl)acetate (HCBIA). In the structure of HSF 1, there are several coordination and lattice H2O units except for the two monodentate CBIA- anions. CP 2 with a one-dimensional (1D) cylindrical structure has free CBIA- units and free H2O units located in the cavity. Thanks to the ability of the uncoordinated carboxyl groups and coordination/lattice water molecules to construct the rich H-bonding networks, both complexes exhibit super-high proton conductivities, reaching 5.09 × 10-3 and 3.41 × 10-3 S cm-1 under 100 °C/98% relative humidity (RH), respectively. Based on the exploration of crystal structure data, combined with the calculated activation energy, and adsorption/desorption plots of nitrogen and water vapor, the causes and differences in proton conductivity of the two complexes, especially the proton-conductive mechanism, are compared and analyzed. This study again confirms that the zwitterionic ligands can exert important effects on forming organo-inorganic hybrid materials with high proton conductivity.