Study On The Synthesis,Structure And Catalytic Properties Of Polyoxomolybdates

Polyoxometalates(POMs)represent an excellent inorganic building blocks with enormous range of structures and excellent physical and chemical properties,such as redox properties,high negative charge and adjustable pH.The design and synthesis of new functional materials based on polyoxometalates using specific POM building blocks have become one of the main directions in POM chemistry.In this paper,we use molybUovanadates[No6V2O26]6-and Evans-ShoWell type polyoxoanion[Co2Mo10O38H1]6-as building blocks,by react with lanthanide cations,transition metals and organic subunits,we have synthesized a series new compounds.These compounds are characterized by elemental analysis.IR,UV-Vis,TG,PXRD and single crystal X-ray diffraction.Moreover,the catalytic properties of these compounds have also been systematically investigated.This dissertation is divided into four parts.1.Pive novel compounds 1-5 constructed from molybdovanadates[Mo6V2O26]6-and lanthanide cations Ln3+(Ln = La,Ce,Nd,Sm,Eu)are prepared by conventional solution method.Compounds 1-5 represent the first examples of inorganic species based on molybdenum-vanadium polyoxometalates and lanthanides.The diffuse reflectance U-V-Vis spectra imply that compounds 1-5 are potential semiconductors with narrow band gaps.All compounds as heterogeneous Lewis acid-base catalysts are very efficient in the cyanosilylation of carbonyl compounds under solvent-free conditions,and compound 3 can be recovered and reused without displaying any significant loss of activity.Furthermore,these compounds also show good activity for photodegradation of organic dye RhB.2.Four inorganic-organic hybrid compounds 6-9 constructed from Evans-Showell type polyoxoanion[Co2MO10O38H4]6-,lanthanide cations(Ln = La3+,Nd3?)and 3-(4-pyridyl)acrylic acid(4-Hpya)have been synthesized by adjusting pH values.The compounds 6 and 7 are isostructural and exhibit a 1D inorganic chain by the linkage of lanthanide ions and[Co2Mo10H4O38]6-units when pH=2.6,protonated 4-H2pya molecules are distributed around the 1D chain via electrostatic interaction.The compounds 8 and 9 are isostructural and exhibit a 1D double-chain constructed from[Co2MO10H4038]6-units and[Ln2(4-Hpya)4]6+(Ln = La,Nd)when pH = 4.1.Four compounds show good photocatalytic activity for the degradation of the organic dye RhB under visible light.The photocatalytic mechanism has also been studied.3.Five interesting inorganic-organic hybrid compounds 10-14 constructed from Evans-Showell type polyoxoanion[Co2Mo10O38H4]6-,lanthanide cations Ln3+(Ln =Sm3+,Eu3+,La3+)and 4,4'-bipyridine-N,N'-dioxide(dpdo)have been synthesized via layering method.The compounds 10 and 11 are isostructural and exhibit a 3D supermolecular structure by Ln-dpdo(Ln= Sm,Eu)building blocks linked with polyoxoanions[Co2MO10O38H4]6-through hydrogen bonds when pH = 3.8.The compounds 12 and 13 are isostructural and exhibit a novel infinite 2D sheet with unusual square voids constructed from lanthanide ions Ln3+(Ln= Sm,Eu)and dpdo molecules when pH = 2.5,the[Co2MO10O38H4]6-polyoxoanion entities function as counteranions locating on the sides of the 2D sheet by electrostatic interaction.Compounds 12 and 13 represent the first 2D organic-inorganic hybrid structures based on Evans-Showell type POMs.In compound 14,the[Co2Mo10H4O4O38]6-clusters fuse two La-dpdo chains together,resulting in 1D ladder-like chain.Compound 12 exhibit high catalytic activity in the cyanosilylation of carbonyl compounds and can be recovered and reused without displaying any significant loss of activity.4.Four inorganic-organic hybrid compounds 15-18 based on Evans-Showell type polyoxoanion[Co2Mo10O38H4]6-have been synttesized by solvothermal strategy using transition metal cations and rigid or flexible N-donor lisgands(4,4'-bipyridine = 4,4'-bipy,1,2-bis(4-pyridyl)ethane = bpe,1,3-di(4-pyridyl)propane = bpp,1,2,4-Triazole = Trz).Crystal analysis reveals that compound 15 exhibits a 1D staggered-ladder-like chain constructed from[Co2M010H4O38]6-and zinc-4,4'-bipy complexes.Compound 16 shows a 1D zig-zag polymeric chain by the linkage of zinc-bpe complexes and[C02MO10H4O38]6-.In compound 17,[Co2Mo10O38H4]6-units are linked by zinc ions to form ID inorganic chain,protonated H2bpp molecules can be connected up together by directional hydrogel-bonding interactions to construct a 3D supramolecular framework.Compound IS consists of a linear trinuclear zinc units bridging six Trz ligands and a[Co2Mo10O38H4]6-unit as the counter anion,which the extensive hycdrogen-bonds exist in the clusters forming a 3D supramolecular framework.Compounds 15 and 16 represent the first extended organic-imorganic hybrid structures based on Evans-S-howell type POMs.We have studied the hetrerogeneous Lewis acid-base catalytic activity of compound 16.