Magnetic properties of a metal-organic porous network [Ni2(BODC)2(TED)]

A new material [Ni2(BODC)2(TED)], (BODC=4,4′-bicyclo[2.2.2]octane dicarboxylate and TED=triethylene-4,4′-diamine), which is a guest-free, porous metal-organic coordination network, has been successfully synthesized. The crystal structure of this compound is tetragonal with the space group P4∕mmm. It is a three-dimensional network that can be deconstructed into rectangular gridlike layers along ab planes. These planes are formed by BODC and Zn2O4 paddle-wheel-like clusters, and the TED ligands from the axial directions of the paddle-wheels connect the layers into a three-dimesional structure. There are no guest molecules found in the pores. The shortest Ni–Ni distance within the paddle wheel is found to be 2.613Å. Magnetic susceptibility χ(T)=M(T)∕H and isothermal magnetization M(H) measurements have been measured on powder samples of this compound. The results of χ(T) show that there is a rapid increase in the susceptibility below 20K due to a spontaneous ordering of the Ni2+ moments. The effective moment μeff of Ni2+ is about 2.20μB at room temperature. The M(H) result at 1.8K shows a clear hysteresis with a coercivity of Hcoe≈1700G. The behavior of this compound is discussed in terms of Ni–Ni coupling within the Ni dimers and dimer chains.