Metalo Hydrogen-Bonded Organic Frameworks Self-Assembled by Charge-Assisted Synthons for Ultrahigh Proton Conduction

Hydrogen-bonded organic frameworks(HOFs) have been well recognizedfor constructing solid-state proton-conducting materials due to theirinherent well-defined H-bonded networks; however, the design and synthesisof stable HOFs showing ultrahigh superprotonic conductivity is stillchallenging. Herein, we reported a facile and effective syntheticstrategy to build high proton-conducting metalo hydrogen-bonded organic-inorganicframeworks (MHOFs) through charge-assisted inorganic and organic synthons.The supramolecular self-assembly of simple metal salts and tetra-carboxylicacids gives rise to two hydrogen-bonded frameworks, [M(H2O)(6)][H(2)tcba] (M = Zn2+, Ni2+; H(4)tcba = 1,2,4,5-benzenetetracarboxylic acid). X-raycrystallography and gas adsorption confirmed the nonporous natureof the HOIFs. Variable-temperature single-crystal and powder X-raydiffraction experiments reveal the thermal and water stability ofthe supramolecular structures sustained by exclusively charge-assistedhydrogen bonds. The high density of carboxylic acid groups and coordinatedwater molecules provide ample protons and hydrophilic environmentsfor efficient proton transport; therefore, variable-temperature and-humidity electrochemical impedance spectroscopy revealed that MHOFsare good supramolecular proton conductors with conductivities up to1.1 x 10(-2) and 2.1 x 10(-2) S center dot cm(-1) for 1 and 2, respectively, at 80 degrees C under 97% RH. Our study demonstratesgreat potential of charge-assisted inorganic and organic synthonsin the design and construction of proton-conducting HOIFs. Two supramolecular proton conductorssynthesized throughcharge-assisted inorganic and organic synthons were reported to showconductivity up to 10(-2) S cm(-1) level because of exclusively charge-assisted hydrogen bonding networks.