| The main objective of this thesis is the synthesis of new polyoxovanadates(polyoxoniobates)derivatives based on different vanadium(niobium)-oxygen cluster building units,which are decorated or bridged by various transition metal and transition metal complexes,these compounds have been hydrothermally prepared with novel structure,good stability and unique properties.We investigate the synthesis condition and influence factors of these novel compounds,and also study the correlations between their structures and performances of these compounds.They were characterized using the X-ray single-crystal diffraction,infrared spectrum,elemental analysis,powder X-ray diffraction,thermogravimetric analysis,and diffused reflectance spectrum.The magnetic property,luminescent properties,photocatalytic activities,selective adsorption and ion-exchange properties of these compounds have been studied.1.The first vanadogermanate dimer,{[Cd(en)2][Cd(en)]2Ge8V12O40(OH)8}2{[Cd(en)(H2O)]2}·en·2H2O(1)(en = ethylenediamine),was hydrothermally synthesised by the reaction of NaVO3,GeO2,Cd2+,H2C2O4·2H2O and en in water.The dimer contains two novel di-Cd-substituted anions[(en)2Cd2Ge8V12O40(OH)8]4-,two[Cd(en)2]2+ supporting groups and a binuclear{[Cd(en)(H2O)]2+}2 bridges.Then,the adjacent dimers are further extended by a pair of bridging[Cd(en)2]2+ complexes to form a 1D hybrid sinusoidal chain.All V ions are present in the valence of +4,and linked together by di-?-O bridges.The magnetic behaviour demonstrates the antiferromagnetic interactions within the V? centers.Furthermore,luminescence measurements demonstrate an intense blue luminescent emission in the solid state.2.A pure inorganic 3D nickel-vanadate bimetallic compound[Ni(H2O)2V2O6](2)was obtained by hydrothermal reaction of Ni2+ and NaVO3.2 represents the first nickel-vanadium framework with a pair of right-and left-handed double helixes,constructed from {NiO4(H2O)2}octahedra and {VO4} tetrahedral.Structurally,the separated Ni2+ centers(Ni2+…Ni2+separations,5.4033 A)linked by a pair of O-V-O bridges that provides a relatively efficient pathway for antiferromagnetic coupling.Compound 2 exhibits an intense broad emission between 400 and 750 nm with a maximum at 525 nm upon excitation of 380 nm.The origin of the luminescence of 2 can be attributed to the charge transfer of an electron from the oxygen 2p orbital to the vacant 3d orbital of V5+ within the V04 tetrahedra.3.Two new cadmium-vanadate hybrid compounds,[Cd5(OH)4V2O8](3)and[(en)Cd2V2O7](4)(en = ethylenediamine),were hydrothermally prepared by the reaction of Cd2+,V2O5 and en.The CdO6 octahedron and VO4 tetrahedron are joined together by edge and corner-sharing O atoms to form heterometallic oxide 3.Compound 4 is a 3D framework constructed from the Cd-O sheets and two types of linkers,inorganic V2O7 dimer and organic en molecule.Because both of the compounds can absorb visible light,herein,MB was used as a model organic dye to evaluate the photocatalytic activities.The experimental results show that two compounds are both active for the decomposition of MB under visible light irradiation.While 3 exhibits a high activity owing to the relatively strong visible absorption and smaller bandgap sizes,with degradation rate reached 92%.Besides,repetitive photocatalytic experiment suggest that 3 is an efficient recoverable photocatalyst.4.A novel inorganic-organic hybrid cobalt vanadates[Co(L)V2O6](L =2-(2-Pyridyl)imidazole)(5),has been synthesized under hydrothermal conditions and further used as catalyst to oxidize olefin to corresponding epoxide using hydrogen peroxide as the oxidant.The results show that under optimized conditions,compound 5 exhibit excellent catalytic performance,with conversion up to 93.2%.As heterogeneous catalysts,compound 5 can be recycled while maintaining its activity in the oxidation of olefin.5.Compound 6 was synthesized by hydrothermal method using[Nb6O19]8-as the precursor to react with NaVO3,NaAsO2,Cu2+ and dap under alkaline conditions,yielding an arsenicniobate-based 3D framework[Cu(dap)2]4[AsNb12O40(VO)4](OH).7H2O(6).Notably,the construction of arsenicniobates-based 3D frameworks is the first time in niobate chemistry,and a tetra-vanadyl capped Keggin arsenicniobate {AsNb12V4} cluster as building unit.Owing to the micropore structure of 6,we measured the adsorption isotherms of water and ethanol at 298 K.The adsorption isotherms indicate that 6 can selectively adsorb water molecules over ethanol to make them separate and can be further used for the separation of azeotrope.Meanwhile,6 is a rare cationic framework,where OH-anions are located.As a result of the compositional features,we performed toxic SCN-removal via anion exchange under ambient conditions,anion-exchange studies suggest that 6 can efficiently remove toxic SCN-anions in aqueous solution. |
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