pH-Controlled Assembly of Two Polynuclear Dy(III)-Containing Polytungstoarsenates with Magnetic and Luminescence Properties

Two novel polynuclear dysprosium (Dy)-containing polytungstoarsenates, CsK7Na16[(AsW9O33)(6)Dy-6-W10O24(H2O)(23)].40H(2)O (1) and Cs2K18Na18[(AsW9O33)(7)Dy-7-W8O21(H2O)(17)(mu(3)-OH)(OH)].78H(2)O (2), have been synthesized via the reaction of the preformed polyoxometalate (POM) precursor [As2W19O67(H2O)](14-) and Dy3+ ions through controlling pH. The polyanion of 1 can be described as a dimer of two similar trimers {(AsW9O33)(3)Dy2W5O12(H2O)(6)} that are linked by Dy cation and two mu(2)-oxo groups, and the Dy(III) ions in 1 are arranged in a linear fashion. Compound 2 presenting an interesting W-shaped structure, assembly composed of a dimeric {(AsW9O33)(2)W3Dy2O8(H2O)(7)}, a trimer {(AsW9O33)(3)W4Dy2O11(OH)(H2O)(3)}, and a particular sandwiched {(AsW9O33)(2)WDy3O4(mu(3)-OH)(H2O)(7)} segment concatenated by mu(2)-oxo groups. The solid-state luminescence performances and lifetime decay behaviors of 1 and 2 were systematically researched at ambient temperature, and time-resolved fluorescence spectra of 1 and 2 indicate energy transfer (ET) from the photoexcitation O -> M ligand to the metal charge-transfer (LMCT) bands of the POM ligands to Dy3+ ions. Moreover, the dynamic magnetic measurement indicates that 1 and 2 exhibit slow relaxation of the magnetization.