Construction Of Polyoxometalate-based Composite Materials For Catalysis And New Functionality

The design,synthesis and characterization of new polyoxometalates（POMs）-based functional composite materials have attracted much attention in recent years.Since the new materials are not simply connected POM and organic ligands through the chemistry bonds but also concentrate the advantage of both components in functions.POMs,as a unique type of metal-oxo clusters with various shapes,sizes and charges,acid and redox properties,have been widely used in catalysis,nanomaterials,medicines and materials with optical,electronic,and magnetic properties.According to the requirement of application,the composites of POMs and various types of functional molecules,for instance,metal-organic molecules,metal-organic complexes and pure organic molecules,can hopefully optimize the structures and the properties of organic precursors.Research on this kind of materials,is expected to expand the application field of POM chemistry.Based above considerations,four new kinds of POMs-based composites materials have been designed.Furthermore,the properties of these materials such as chiral catalysis,fluorescence,and the dye adsorption have been investigated.1.Chiral cyclohexanediamines are connected covalently to two monolacunary polyanions [PW₁₁O₃₉]7-,[SiW₁₁O₃₉]8-by organsilicone and three novel POMs-based chiral materials have been isolated: D,S-[（C4H9）4N]3{PW₁₁O₃₉O[Si（CH₂）3-（1R,2R）-NHC6H10NH₂]2}·3DMF（1）D,S-[（C4H9）4N]4{SiW₁₁O₃₉O[Si（CH₂）3-（1R,2R）NHC6H10NH₂]2}·DMF（2）Asymmetric Aldol and asymmetric cyanohydrin catalysis studies reveal these compounds represent high catalytic activities and good chiral selectivities.The ee value of commpoud 2 in Aldol reaction is 96%;the ee value of compound 2 in asymmetric cyanohydrin reaction is 93%.In addition,these catalysts are easy to recycle and little degradation in catalystic efficiency has been found after times of cycles.Configurations of catalysts in the catalytic system and possible catalytic mechanisms have been analyzed by quantitative calculations.2.The composite of MnIII（salen）（salen = N,N-bis（salicylidene）ethylenediamine）cations with different kinds of polyanions by electrostatic attraction or coordination bonds have obtained three POMs-based MnIII（salen）functional materials 4-6.[Mn（3,5-tBu-salen）（H₂O）₂]₃[PW₁₂O₄₀]·9H₂O（4）[Mn（3,5-tBu-salen）（H₂O）₂]₂（H₃O）[CrMo₆O₂₄H₆]（5）[Mn（3,5-tBu-salen）（H₂O）]₂[MoO₄] ·5H₂O（6）Chiral sulfides catalyst reactions reveal the conversion rates of benzoic sulfide oxidation for sulfoxide and sulfone within 20 min are 100% and 95% for homogeneous catalysts 4 and 5,respectively.During the reaction of the catalytic benzoic sulfide oxidation for chiral sulfoxide,compound 6 shows catalytic activity.And the conversion rate is 93%,chiral ee value is 43%.3.Two new POM-based inorganic-organic hybrids have obtained by self-assemble of [Mo7O24]6-,metal ions and bbtx ligands under hydrothermal condition.[Cu（bbtx）₃][Mo₆O₁₉]（7）[Ag₂（bbtx）₂][Mo₆O₁₉]（8）Compound 7 shows only intrinsic fluorescence behavior of the bbtx ligands.Compound 8 exhibits reversible thermochromic luminescence property which is aroused by the charge transitions between Ag+ ions and ligands.Because of the existence of polyanion,Ag+ ions directly reduced to elemental silver upon irradiation with visible light,which broke the coordinated bonds between ligand and Ag+ ions and quenched the fluorescence.During this processes,POMs play an important role in the photo-catalysis reactions.The formation of the elemental silver and the broken of Ag-N bonds after irradiation have been proved in the catalytic reaction of reduction of nitrophenol.The introduction of POMs into fluorescent complexes lead to a new in situ photoinduced material with fluorescence quenching property,that can be used in optical storage and optical memory materials.4.A new example of composite material [La（CH₃COO）（H₂O）]MoO₄（9）was synthesized by utilizing（NH4）6[Mo7O24],La（NO3）3 and acetic acid in hydrothermal condition.After calcination,a new oxide material composed by La and Mo La2Mo₂O₉ has been obtained.The material represent rapid and selective adsorptions of multi-sulfonic dyes and condensed ring amine dyes.The reason is that La centers and Mo centers possess special adsoption of sulfonic groups and amino groups,respectively.The performance of dyes adsorption and desorption can be adjusted by changing PH or polarity of the solution.Thus,this material can be used in the separation of three mixed dyes.Furthermore,the high thermostability and the tolerance for wide pH range enable the new material separate multi-component dyes and easily reuse.