Hydrogen-bonded nickel(II)-organosulfonate framework: Thermal expansion behavior, proton conduction, and magnetic properties

Metalo Hydrogen-bonded organic frameworks are emerging supramolecular platforms for designing functional molecular materials. Herein, we reported the supramolecular structure, thermal, magnetic, and proton con-duction properties of a hydrogen-bonded nickel(II)-organosulfonate framework, [Ni(H2O)(6)][NPS](2) (NiHOF, HNPS = naphthalene-2-sulphonic acid). Single-crystal X-ray diffraction studies reveal a two-dimensional hydrogen-bonded network sustained by multiple and charge-assisted O-H center dot center dot center dot O H bonds between hex-aaquanickel(II) cations and organosulfonate anions. Additionally, continuous ca. 0.47 x 0.70 nm(2) windows were formed within the framework. The thermal stability of the NiHOF was confirmed by thermal gravimetric analysis and variable temperature single-crystal and powder X-ray diffraction patterns. N-2 sorption isotherms suggest an ultramicroporous supramolecular framework of NiHOF with permanent porosity. The anisotropic positive thermal expansion behavior of NiHOF was evidenced by the dynamic crystallography experiments. Magnetic measurements indicate easy-axis magnetic anisotropy (D = -10.5 cm(-1)) of the NiHOF while no slow magnetic relaxation behavior. Electrochemical impedance spectroscopy indicates the temperature and humidity dependence of conductivities of NiHOF. At 50 degrees C and 70% relative humidity, the conductivity is 1.13 x 10(-4) S center dot cm(-1), revealing a supramolecular proton conductor of NiHOF. This work provides a potential way for designing novel thermal, magnetic, and electrical molecular materials through the supramolecular assembly of inorganic and organosulfonate synthons.