Proton-conducting cobalt(II) hydrogen-bonded organic framework driven by coordinated water molecules with slow magnetic relaxation

Metal hydrogen-bonded organic framework (MHOF) has received ongoing attention because they provide new chances for the design and construction of functional molecular materials. Herein, we reported a rare dual-functional MHOF based on a mononuclear complex, [Co(QLC)2·(H2O)2] (1, HQLC = Quinoline-2-carboxylic acid) with interesting magnetic and electrical properties. Variable-temperature single-crystal diffraction experiments revealed a highly thermal stable three-dimensional (3D) hydrogen-bonded network supported by multiple intermolecular hydrogen bonding and π–π stacking interactions. Importantly, the metal-bound water molecules were found to be critical for the formation of H-bonded 2D layers with the contribution of terminal carboxylic oxygen of QLC. By taking advantage of the enhanced acidity of the coordinated water molecules, variable-temperature and -humility alternating current impedance spectroscopy revealed the compound is a good supramolecular proton conductor with 1.2 × 10−4 S·cm−1 at 70 °C under 97% RH. D.C. susceptibility measurement indicated easy-axis magnetic anisotropy of the Co2+ ions with the experimental D value of -72.1 cm−1 in the complex. Dynamic A.C. susceptibility measurements revealed the compound can display slow magnetic relaxation under an applied dc field. The foregoing results provide not only a rare hydrogen-bonded organic−cobalt framework displaying interesting magnetic and electrical properties but also a promising way to build multifunctional MHOFs via coordinated water molecules.