Syntheses and crystal structures of two compounds based on saturated keggin-type polyoxotungstates and mixed ligands

Two new polyoxotungstates with dafo and 4,4′-bipy ligands, [Ag(dafo)2]2{[Ag(4,4′-bipy)]2SiW12O40} (1) and [Cd2(dafo)4(4, 4′-bipy)(H2O)2](dafo) SiW12O40 (2) (dafo = 4, 5-diazafluoren-9-one, 4,4′-bipy = 4,4′-bipyridine), have been hydrothermally synthesized and characterized by elemental analyses, IR, TG and single crystal X-ray diffraction. Compound 1 consists of a one-dimensional (1D) chain constructed from [Ag(4,4′-bipy)]+ cations. With the connection of [Ag(4,4′-bipy)]+ cations and α-[SiW12O40]4− anions, two-dimensional (2D) structure was built. Because of the π–π stacking interactions between pyridyl rings of 4,4′-bipy from adjacent chains, three-dimensional (3D) structure was generated. Furthermore, the C–H ··· O weak interaction between and polytungstate made the structure more stable. Like 1, compound 2 is a three-dimensional (3D) supramolecular compound constructed from a transition-metal complex fragment [Cd2(dafo)4(4,4′-bipy)(H2O)2]4+, and free dafo through C–H ··· O weak interactions. To our bes...