Metalo Hydrogen-Bonded Organic Frameworks Constructed by Coordinated Chains for Magnetic and Proton-Conductive Bifunctionality.

Abstract

Metalo hydrogen-bonded organic frameworks (MHOFs) have received growing interest in designing crystalline functional materials. However, reports on bifunctional MHOFs showing magnetic and proton-conductive properties are extremely limited and their design is challenging. Herein, we investigated the magnetic and proton-conductive properties of two sulfonated CoHOF and MnHOF, {M(H2O)2(abs)2}n (M = Co2+ and Mn2+, Habs = 4-aminoazobenzene-4'-sulfonic anion), constructed by coordination chains. The supramolecular frameworks sustained by H bonds between -SO3- and coordinated water show directional ladder-type H bonds with hydrophilic nanochannels, leading to high proton conduction with exceptionally high conductivity around 10-2 S cm-1 at 100 °C under 97% relative humidity. In particular, the maximum σ value of CoHOF, 2.11 × 10-2 S cm-1, recorded the highest value among the reported proton-conducting materials showing slow magnetic relaxation. Meanwhile, the molecular structure of organosulfonate enables the magnetic isolation of high-spin Co2+ and Mn2+ centers in the frameworks. Magnetic measurements indicated that the MHOFs show field-induced single-ion magnet (SIM) properties, making these compounds rare magnetic-proton-conductive MHOFs. The work provides not only two unique MHOFs with SIM behavior and high proton conduction performance but also avenues for designing stable bifunctional MHOFs via a coordination chain approach.