Synthesis, Structure And Characterization Of Supramolecular Compounds Based On Transition Metal And Keggin-type Polyoxometalate

In this paper, two new isostructural supramolecular compounds based onKeggin-type polyoxometalate （POM）、transition metal（NiSO₄and ZnSO₄）and3-aminopyrazine-2-carboxylic acid （Hapca）, have been synthesized in aqueoussolution and characterized by single-crystal X-ray diffraction, elemental analysis, TGanalyses, IR and fluorescence spectroscopy.[Ni（Hapca）₂（H₂O）₂]2[SiW₁₂O₄₀]·12H₂O （1）[Zn（Hapca）₂（H₂O）₂]2[SiW₁₂O₄₀]·12H₂O （2）Hapca=3-aminopyrazine-2-carboxylic acidIn1, The two Hapca acting as bidentate ligands coordinate with NiIIequivalently,and then two cations are linked through hydrogen bonds into a dimer[Ni（apca）₂（H₂O）₂]₂⁴⁺. These dimers link together via O…N hydrogen-bondinginteraction to give birth to2D layer with rectangle grids. Anions [SiW₁₂O₄₀]^4-arelocated in the cavities and link the2D layers into3D supramolecular architecture viahydrogen bonds. The compounds represent the first examples of self-assembly of2Dmetal–Hapca complex supramolecular “host” networks formed by hydrogen bondinginteractions and “guest” polyoxoanion species.The TG analyse results of2support its chemical composition.The photoluminescent properties of2and free Hapca were investigated in thesolid state at room temperature. In comparison with the pure Hapca ligand, Theformation of2obviously decrease the emission intensity of the Hapca ligand.