The Inorganic-Organic Hybrid Compounds Based On [SiW₁₂O₄₀]^4-:Synthesis, Crystal Structure And Properties

The study on inorganic-organic hybrid compounds based on polyoxometalates（POMs） is one of the hot spots in recent research on POMs chemistry. Introduction of organic groups in POMs not only can greatly increases the number of compounds, but also can change some properties of POMs, such as stability and molecular recognition.In this paper, hydrothermal method was used to get products. In the experiment,H₄ SiW₁2O₄0·6H₂O and pyrazine-2,3-dicarboxylic acid were used as raw materials. Two new three-dimensional POMs hybrid compounds were obtained which have not been reported by adding different metal salts（MnSO₄, Cu（CH₃COO）₂）. The new compounds are:{Mn₄（pz）₆（H₂O）₂[SiW₁2O₄0]}（1） and{Cu₅（pz）₆（H₂O）（μ₃-O）[Si W₁2O₄0H]}（2）,（pz = pyrazine）Single crystal X-ray studies show that in the compound 1, [Mn₄（pz）₆]_n⁴ⁿ⁺ polymeric cation with 2D layered structure was formed with metal ions and pz which is the product of decarboxylation of the 2,3-pyrazine dicarboxylic acid. Four Mn atoms are in three kinds of coordination environments, two of them have the same coordination environment, which are coordinated by three N atoms of three different pz; the other two are four-coordinated with different coordination environments from the previous, connected with atoms from different groups. The two 2D layers including ten-metal rings are linked through sharing a coordination water into a two-layer structure. [SiW₁2O₄0]^4- anions are embedded in two two-layers through the coordination of Ot atoms to Mn atoms, leading a 3D hybrid compound. In compound 2, all of Cu atoms have taken four coordinated way, but coordination atoms are provided from different groups of atoms. Cu atoms and pz molecules constitute [Cu₅（pz）₆]_n⁵ⁿ⁺polymeric cation with 2D layer structure. The layer contains two types of macrocycles, a six-metal ring and an eight-metal ring. Two such layers form a double-layered structure through μ3-oxygen atom, and [SiW₁2O₄0]^4-anions are embedded between them through the coordination of Ot atoms to Cu atoms, eventually forming a three-dimensional hybrid compound. IR data analyses for 1 and 2 also proved the correctness of the structure due to no characteristic peak of carbonyl group in IR spectra. Thermogravimetric analysis, fluorescence of 1 are also analyzed and discussed.