Assembly And Properties Of POM-based Compounds Constructed By Pyrazole And Pyrazine Derivatives

In this paper,under the hydrothermal conditions,by using pyrazol and pyrazine derivatives as organic ligands,?1H–pyrazol?L1?,2,3–diphenyl–pyrazine?L²?and 2,3–diphenyl–quinoxaline?L³??and tuning the pH of reaction system,varieties of POMs,the filling factor of the Teflon–lined autoclave and so on,ten compounds based on Keggin/Lindqvist polyoxometalate?POM?were synthesized.Their structures were characterized by single crystal X–ray diffraction.Furthermore,the electrochemical and photocatalytic properties of these new POM–based compounds were also explored.1.Under hydrothermal conditions,by using small rigid ligand and different Keggin–based POMs,two compounds with different dimensions were synthetized:[Ag^IL₂¹]₄[Si Mo₁₂O₄₀]?1?,[Ag^IL₂¹]₃[PMo₁₂O₄₀]?2??L1 = 1H–pyrazol?In compound 1,there are two kinds of chains,the chains linked by two [AgL12]+ clusters and the other linked only by one [AgL12]+,which are further connected each other by sharing[SiMo₁₂O₄₀]4– anions to construct a 2D layer.In compound 2,four–supporting [PMo₁₂O₄₀]3–anions are fused by [Ag?1?L12]+ subunits to form a 1D chain.Furthermore,through weak interactions of Ag…O?3.091 ??a 2D supramolecular layer is constructed.2.The pyrazine derivatives own two N donors locating counterpoint of a six–membered conjugate ring,facilitating to link two TMs and form metal–organic chains.However,pyrazine derivatives ligands are scarcely utilized in POM–based compounds.By using two kinds of pyrazine derivatives?2,3–diphenyl–pyrazine?L²??2,3–diphenyl–quinoxaline?L³??as organic ligands,we have synthesized 5 new Keggin–based compounds:[Ag₃^IL₂²?H₂O?₂(PMo₁₂O₄₀)]?3?,[Ag₄^IL₂⁵(SiMo₁₂O₄₀)]?4?,[Ag₆^IL₆³(PMo₁₂O₄₀)2]?5?,[Ag₂^IL₂³(C₁₆H₃₆N)₂(SiMo₁₂O₄₀)]?6?,[Cu₃^IL₃³(PMo₁₂O₄₀)]?7?(L² = 2,3–diphenyl–pyrazine,L³ =2,3–diphenyl–quinoxaline,C₁₆H₃₆ N = tetrabutyl ammonium)In compound 3,[Ag3L²2]3+subunits link the PMo₁₂ anions to construct two kinds of 1D chains and these 1D chains connect each other by sharing the same PMo₁₂ anions and a 2D grid–like layer was built.The asymmetric unit of compound 4 linked each other to form a dimer by sharing Ag ions,and then a 1D double strand was formed.The SiMo₁₂ anions connect adjacent 1D double strands through Ag3–O23 bonds and a 2D network was built.In compound 5,there exists a 1D ladder–like double chain with PMo₁₂ anions as linking bars.Between adjacent chains,by using the linkage of Ag2–O24,a 2D layer is formed.In compound 6,the SiMo₁₂ anions act as inorganic linkages connect adjacent zigzag chains through Ag1–O3 bonds to construct a 2D grid–like layer.In compound 5,two CuI–L³ lines are fused by PMo₁₂ anions to build a 1D ladder–like chain.3.Through using a conjugate ring–riched quinoxaline derivative 2,3–diphenyl–quinoxaline?L³?,three new Lindqvist polymolybdate based compounds were hydrothermally synthesized and structurally characterized:[CuI2L₃³(Mo₆O₁₉)]?8?,[CuI2L₂³(C₁₆H₃₆N)₂(Mo₆O₁₉)2]?9?,[CuI4L₄³Cl₂(Mo₆O₁₉)]?10?(L³ = 2,3–diphenyl–quinoxaline,C₁₆H₃₆ N = tetrabutyl ammonium).In compound 8,the CuI ions as connecting bodies are linked by L³ molecules to form a[CuL³]nn+ metal–organic line,and these lines link the Mo6 anions to construct 1D chains.Then these 1D chains connect each other by sharing the same Mo6 anions and a 2D grid–like layer was built.In compound 9,there is also a [CuL³]nn+ line.The Mo6 anions offering one terminal O atom covalently hang this metal–organic line to construct a wave–like 1D chain of compound 9.There exist two types L³ligands?type–a and type–b?in compound 10.The type–a L³ molecules and Cl–bridging are linked by CuI ions to form a metal–organic line,with the type–b L³ and Mo6 anions covalently hanging it up and down.