Water-Induced Dual Switching of Magnetic Properties and Proton Conduction in a Hydrogen-Bonded Manganese(II)-Organosulfonate Framework

Abstract

Dynamic modulation of magnetic and electrical properties through single-crystal-to-single-crystal (SCSC) transformations has always been difficult. Herein, we report the synthesis, structures, magnetic and proton conduction properties of a dynamic manganese(II) hydrogen-bonded organic framework (MnHOF), formulated as {[Mn(bpy)(H₂O)₄]·2NPS·H₂O}_n (denoted as 1·H₂O, NPS = naphthalenesulfonate, bpy = 4,4′-bipyridine). This framework is assembled from one-dimensional Mn(II) coordination chains interconnected through multiple O–H···O hydrogen-bonding interactions. Upon the loss of lattice water molecules, 1·H₂O undergoes reversible single-crystal-to-single-crystal (SCSC) transformation to yield a dehydrated phase, {[Mn(bpy)(H₂O)₄]·2NPS}_n (1). Interestingly, the dehydrated phase 1 can recover to 1·H₂O through the gain of lattice water molecules from air atmosphere in an SC-SC manner. Remarkably, the structural transition induces a substantial reorganization of the hydrogen-bonded networks and the structure modulation of bridging bpy during the dehydration–rehydration process, which effectively modulates magnetic and proton-conducting pathways and enables reversible switching of magnetic interaction and proton conductivity between “on” and “off” states. At 90 °C and 97% RH, compound 1·H₂O displays superionic proton conductivity, achieving a significant conductivity of 2.85 × 10^–3 S cm^–1, which is due to continuous 1D hydrogen-bonded chains. This study demonstrates the promising potential of MHOFs for designing dynamically responsive bifunctional proton-conducting magnetic materials.