Magnetic relaxation behavior of lanthanide substituted Dawson-type tungstoarsenates

Two new polyoxometalate compounds [(CH3)4N]8[Ln(H2O)8]2[(α2-As2W17O61)Ln(H2O)2]2·nH2O (Ln=Er (1), Dy (2)) have been prepared by the trivacant Dawson-type anion [α-As2W15O56]12− and trivalent rare earth ion and characterized by single-crystal X-ray diffraction, IR spectra, thermogravimetric and electrochemical analyses. The centrosymmetric polyoxoanion, {[(α2-As2W17O61)Ln(H2O)2]2}14−, bounded to each other via Ln3+ connecting to terminal W–O oxygen atoms. Furthermore, the polyoxoanions are linked by [Ln(H2O)8]3+ to form an extensive 3D supramolecular network structure depending on hydrogen bond. The magnetic properties of the two compounds have been studied by measuring their magnetic susceptibilities in the temperature range 2.0–300.0 K, indicating the depopulation of the stark components at low temperature and/or very weak antiferromagnetic interactions between magnetic centers. Low-temperature ac magnetic susceptibility measurements reveal a slow magnetic relaxation behavior for 2.