Supramolecular assembly, structure, magnetic property, and proton conductivity of a nickel(II) hydrogen-bonded organosulfonate framework

A three-dimensional nickel(II) hydrogen-bonded organic framework (NiHOF), formulated as [Ni(H2O)2(EtOH)2(MeCN)2][nds] (NiHOF-HGNU-2, H2nds = 1,5-Naphthalenedisulfonic acid, HGNU = Huanggang Normal University), was synthesized and magnetically and electrically characterized. Single-crystal X-ray diffraction (SC-XRD) analysis revealed that extensive hydrogen bonding interactions formed between the [Ni(H2O)(EtOH)(MeCN)]2+ cations and organodisulfonate anions nds2−, leading to a highly hydrogen-bonded network. Variable-temperature SC-XRD and thermogravimetric analysis both reveal the crystalline sample of NiHOF-HGNU-2 can be thermally stable up to 400 K. Magnetic investigations reveal the uniaxial magnetic anisotropy (D = -9.87 cm−1) of the distorted octahedral Ni2+ ions of NiHOF-HGNU-2 without slow magnetic relaxation. Alternating current impedance spectroscopy indicate NiHOF-HGNU-2 exhibits temperature- and humidity-dependent proton conduction behavior with the highest measured conductivity reaching 1.15 × 10−4 S cm−1 at 85°C and 98% relative humidity, suggesting a supramolecular proton conductor of the NiHOF-HGNU-2. The forgoing results not only provide a new Ni-based proton conductor but also an organodisulfonate strategy for building supramolecular proton-conducting materials.