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

Abstract

Hydrogen-bonded organic frameworks (HOFs) have been well recognized for constructing solid-state proton-conducting materials due to their inherent well-defined H-bonded networks; however, the design and synthesis of stable HOFs showing ultrahigh superprotonic conductivity is still challenging. Herein, we reported a facile and effective synthetic strategy to build high proton-conducting metalo hydrogenbonded organic−inorganic frameworks (MHOFs) through charge-assisted inorganic and organic synthons. The supramolecular self-assembly of simple metal salts and tetracarboxylic acids gives rise to two hydrogen-bonded frameworks, [M(H 2 O) 6 ][H 2 tcba] (M = Zn 2+ , Ni 2+ ; H 4 tcba = 1,2,4,5-benzenetetracarboxylic acid). X-ray crystallography and gas adsorption confirmed the nonporous nature of the HOIFs. Variable-temperature single-crystal and powder X-ray diffraction experiments reveal the thermal and water stability of the supramolecular structures sustained by exclusively charge-assisted hydrogen bonds. The high density of carboxylic acid groups and coordinated water molecules provide ample protons and hydrophilic environments for efficient proton transport; therefore, variable-temperature and -humidity electrochemical impedance spectroscopy revealed that MHOFs are good supramolecular proton conductors with conductivities up to 1.1 × 10 −2 and 2.1 × 10 −2 S•cm −1 for 1 and 2, respectively, at 80 °C under 97% RH. Our study demonstrates great potential of charge-assisted inorganic and organic synthons in the design and construction of proton-conducting HOIFs.

Magnetic and Porous Regulation in Cobalt(II) Hydrogen-Bonded Organic Framework via Supramolecular Isomerism

“…Notably, incorporating inorganic moieties offers an alternative approach to enhance stability and introduce new functions to HOFs. To this end, metalo hydrogen-bonded organic–inorganic frameworks (MHOFs) have emerged as a significant subclass of HOFs. − For instance, magnetic MHOFs has gained attention as a new type of single-ion magnets (SIMs), which exhibit magnetic bistability at the single-molecule level. , Despite numerous reports on SIMs and HOFs, magnetic MHOFs with slow magnetic relaxation behavior remain exceedingly rare. ,,, The combination of SIMs and HOFs, termed as SIM-HOFs, potentially provides a novel way to regulate the magnetic behavior of these complexes by taking advantage of HOF’s unique characteristics.…”

Self-assembly of water-filled molecular saddles to generate diverse morphologies and high proton conductivity

“…28 Such organic SSPC materials can benefit from exploiting supramolecular interactions such as hydrogen bonding, π-π stacking, and CH-π interactions, as well as charge transfer (CT) interactions to direct molecular self-assembly in order to create proton conducting conduits that ease the flow of H + through them. [29][30][31] These interactions play a crucial role in stabilizing the functional supramolecular self-assemblies. [32][33][34] Thus, understanding the principles underlying the self-assembly process and its impact on the resulting structural arrangement is essential for enhancing the proton conducting ability.…”

Latest progress in proton-conducting hydrogen-bonded organic frameworks

“…So far, a variety of H-bonded units, covering diaminotriazine (DAT), carboxylate, azacyclo-units, and other units, have been employed to construct porous and stable HOFs. HOFs are widely used as emerging multifunctional substances in gas storage and separation, 67–70 molecular sensing, 71–74 heterogeneous catalysis, 75–78 biological applications, 79–81 photoluminescent materials, 82–86 proton conduction 87–92 and membrane-based applications. 93–96 To date, although there have been some reviews on the preparation and application of HOFs, 97–101 reviews on proton conductivity are relatively rare.…”