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 center dot(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 11-11 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 x 10-4 S center dot cm- 1 at 70 degrees 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.