Synthesis, Crystal Structure And Characterization Of Silver-Polyoxotungstates

In this paper, three unreported compounds based on Strandberg and Kegginclusters have been synthesized by adjusting reaction materials and reaction conditions.These compounds are structurally characterized by elemental analyses, IR, TGanalysis and single crystal X-ray diffractions. The luminescent properties of thesecompounds are tested in the solid state.1. A new compound based on the Strandberg-type cluster was synthesized andcharacterized by liquid diffusion method:[Ag₁₂（OH）₂（H₂O）₄KNa(P₂Mo₅O₂₃)₂]（1）In1, two crystallographically independent P₂Mo₅clusters are surrounded bythirty-seven Ag+ions, three K+ions and three Na+ions, representing the highestconnection number of the Strandberg-type POMs to date. There are twelvecrystallographically unique silver cations, which have different coordinationgeometries: distorted triangular prism, distorted octahedron, distorted square-pyramidand distorted trigonal bipyramid. All the Strandberg-type units are interlinked by Ag （I）forming a3D arrangement through O-Ag-O bridging bonds. By testing TG, thecompound1is poor thermal stability. The formation of the compound1weakens theluminescence property of P₂Mo₅cluster.2. Under aqueous synthesis condition, two new compounds have been gained,based on Keggin polyoxoanions (H2W₁₂O₄₀and SiW₁₂O₄₀) as building blocks andsilver ions as connecter:[K₂Ag₈（pydc）₂（Hpydc）₂（H₂O）₄SiW₁₂O₄₀]4H₂O （2）（NH₄）₄[KAg₂（Hpydc）（H₂O）_4.5(H₂W₁₂O₄₀)]·4H₂O （3）H₂pydc=pyridine-2,3-dicarboxylateIn2, six-nucleus [Ag₆（Hpydc）₂]⁴⁺units and two-nucleus [Ag2（pydc）2]2-units arelinked alternately through oxygen atoms of the carboxylic group leading to a grid-like2D layer. These grid-like2D layers are supported by SiW₁₂clusters, giving a unique3D framework. In3, each H2W₁₂O₄₀cluster connects five Ag ions and three K ions,acting as an octadentate bridging linker. Each Ag2ions links three H2W₁₂O₄₀clusters.These neighbouring units, related by an inversion centre, are connected through Ag1and Ag2into double chains. Furthermore, these double chains are linked togetherthrough K⁺ions to form a3D framework. By testing TG, the compound2is better thermal stability while compound3is poor thermal stability. The formation of thecompounds2and3weaken the luminescence property of H2pydc ligand.