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Two novel polynuclear dysprosium (Dy)-containing polytungstoarsenates, CsK7Na16­[(AsW9O33)6­Dy6W10O24(H2O)23]·40H2O (1) and Cs2K18Na18­[(AsW9O33)7­Dy7W8O21(H2O)17(μ3-OH)­(OH)]·78H2O (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)3Dy2W5O12(H2O)6} that are linked by Dy cation and two μ2-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)2W3Dy2O8(H2O)7}, a trimer {(AsW9O33)3­W4Dy2O11­(OH)­(H2O)3}, and a particular sandwiched {(AsW9O33)2WDy3O4(μ3-OH)­(H2O)7} segment concatenated by μ2-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.

Two series of lanthanoid (Ln)-containing polyoxometalates (POMs) {[Ln6(ampH)4(H2O)24–n (ampH2) n (PW11O39)2]·21H2O (Ln = Tb, n = 0 (1), Ln = Er, n = 1 (2)) and K2[Ln6(ampH)4(H2O)22(SiW11O39)2]·23H2O (Ln = Tb (3), Er (4)) (ampH2 = (aminomethyl) phosphonic acid)} have been synthesized with tri-lacunary Keggin-type POMs containing different types of heteroatoms. Compounds 1 and 2 display neutral organic–inorganic hybrid POM molecules containing {Ln6(ampH)4} ({Ln6}) cores sandwiched by two {PW11O39} units. By changing the heteroatoms from PV to SiIV, the extended 2D networks of 3 and 4 were successfully isolated where the adjacent {Ln6} clusters were connected by {SiW11O39} moieties. Luminescence performances and magnetic properties of 1–4 have been systematically surveyed. The solid-state fluorescence spectra of 1–4 display characteristic emissions of Ln components resulting from the 4f–4f transitions, and energy transfer from the POM segments to Ln3+ centers in 1 and 3 has been observed based on the lifetime decay behaviors. Furthermore, all compounds can be utilized as electrocatalysts toward reduction of nitrite with high stability.

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