Syntheses,Electrochemical Sensors And Photocatalytic Properties Of POM Compounds Based On Pyrazole And Pyrazine Derivatives

In this work,pyrazole and pyrazine derivatives are used as organic ligands under hydrothermal conditions,such as 1’-bis（3,5-dimethyl-1H-pyrazole） methane（H₂bdpm） and1,2-bis（1H-pyrazolyl） ethane（H₂bhpe）,2,3-di Pyridin-2-yl-pyrazine（L¹）,2,3-di-pyridin-2-yl-quinoxaline（L²）.By changing the reaction system conditions,such as pH,POM types and temperature,12compounds based on Keggin,Wells-Dawson and polymolybdate POM anions were obtained.These structures were characterized by X-ray single crystal diffractometry.In addition,we have also studied the electrochemical sensors and photocatalytic properties of these new POM-based compounds.1.Under hydrothermal conditions,we obtained three Wells-Dawson compounds containing mononuclear,binuclear and trinuclear clusters by adjusting different TM（Co^Ⅱ,Cd^Ⅱ,Cu^Ⅱ） and organic ligands.The electrochemical and photocatalytic properties of compounds 1-3 were investigated.[Co^Ⅱ（edpz）（H₂bdpm）₃][(H₄P₂W₁₈O₆₂)]（1）[Cd₂^Ⅱ（mpz）（H₂bhpe）_2.5（H₂O）(H₂P₂W₁₈O₆₂)]·（ppz）·6H₂O（2）[Cu₃^Ⅱ（ppz）（H₂bhpe）₂(P₂W₁₈O₆₂)（H₂O）₃]·2H₂O（3）H₂bdpm=1,1’-bis（3,5-dimethyl-1H-pyrazole）methane,H₂bhpe=1,2-bis（1H-pyrazolyl） ethaneedpz=4-ethyl-3,5-dimethyl-1H-pyrazole,mpz=4-methyl-4H-pyrazole,ppz=4-propyl-1H-pyrazoleIn compound 1,one Co^Ⅱ ion connects four ligands and forms a mono-nuclear cluster.Compound 2 shows a bi-nuclear Cd^Ⅱ cluster with two Cd^Ⅱ ions fused to six ligands.The P₂W₁₈ anion connects the bi-nuclear Cd^Ⅱ clusters to form a three-dimensional framework.In compound 3,five ligands were linked to three Cu^Ⅱ ions to construct a tri-nuclear cluster.2.Six POM-based metal-organic loop compounds were constructed under hydrothermalconditionsusingthedoublechelatingligands2,3-dipyridin-2-yl-pyrazine（L¹） and 2,3-dipyridin-2-yl-quinoxaline（L²）.[Ag₄^I（L¹）₄(SiMo₁₂O₄₀)]（4）[Cu₆^Ⅱ（L¹）₆（H₂O）₆(SiMo₁₂O₄₀)₃]·6H₂O（5）[Cu^Ⅱ（L¹）（H₂O）(β-Mo₈O₂₆)_0.5]（6）[Ag₂^I（L²）(β-Mo₈O₂₆)_0.5]（7）[Cu^Ⅱ（L²）(β-Mo₈O₂₆)_0.5]（8）[Zn^Ⅱ（L²）(β-Mo₈O₂₆)_0.5]（9）We obtained compounds 4 and 5 at first containing tetranuclear and hexanuclear metal organic loops using L¹.By changing SiMo₁₂ to Mo₈O₂₆,a 2D non-loop structure of 6 was formed.In addition,by changing the steric hindrance of the ligand,we introduced L² and different transition metal ions to construct three 2D compounds 7-9 with a binuclear metal-organic loop.3.For the uncertainty of hydrothermal reaction,purposeful syntheses of compounds are very challenging,and the structure of the regulatory compounds is of great significance.In this chapter,we used the quinoxaline derivative dpq as a ligand to obtain the compounds 10-12 by adjusting the reaction conditions:pH,reaction time and temperature.[Ag₂（dpq）][(H₃Mo₃O₁₀)]（10）[（dpq）₂(H₄SiMo₁₂O)]·8H₂O（11）[Ag₂（dpq）₂(HSiMo₁₂O₄₀)]（12）In compound 10,a continuous POM unit appeared:Mo chain structure.The ligand is attached by Ag^I on both sides of the Mo chain.Then it expands to the next Mo chain to build a 2D layer structure.Compound 11 forms a 1D supramolecular chain and a 2D supramolecular layer by hydrogen bonding between the SiMo₁₂ and dpq ligands.In compound 12,the coordination mode of POM is interesting,and one terminal oxygen and two bridging oxygen participate in the construction of the 1D chain.Research on the construction of high-dimensional structures is underway.In addition,we studied the electrochemical properties and the UV degradation properties of MB as catalysts of compounds 10-12.