Preparation Of Zn 4 -ε-Keggin POMOFs And Their Electrochemical Catalysis And Sensing

Polyoxometalate(POM)ions,which represent a well-defined library of inorganic building blocks of nanoscopic scale with oxygen-rich surfaces,are ideal candidates for the design and construction of templated framework materials.POM-based MOFs materials(POMOFs)can be constructed by replacing the metal ions(or metal clusters)in the routine MOFs with size-matched polyoxoanions.A number of studies have indicated that POMOFs materials have a lot of active physical and chemical properties,such as magnetic,photochemical,electrical,and catalytic properties.Among them,the electrochemical properties of POMs in POMOFs aroused great interest of researchers on account of their potential applications in electrocatalysis and electrochemical analysis.In this thesis,we isolated a series of novel POMOFs materials by using the ε-Keggin anions as the basic building block,together with rigid carboxylic ligands and transition metal ions(Zn2+).They were characterized by IR,TG,powder X-ray diffraction and single crystal X-ray diffraction analyses.The electrochemical behavior and electrocatalytical activity of them were studied.The major results were listed as follows:1.A novel 2D network of 1,[TBA]3[H2PMoⅤ8MoⅥ4O40][Zn4MIP],was isolated by using the bridging ligand of H2MIP(5-methylisophthalic acid)as the linker.Through the linkage of Zn-O bond,the {ε-H2PMoⅤ8MoⅥ4O40Zn4} is extended to form a 1D inorganic chain along the b axis.The distance between layers is 15.89 A.The proton conductivity of 1 was also evaluated.2.Two two-fold interpenetrated 3D networks(2 and 3)on the basis of {Zn4-ε-Keggin}dimer were constructed by using two types of terphenyl-based tricarboxylates of H3LI(3,5’,3"-position substitution)and H3L2(4,5’,4"-position substitution)under hydrothermal condition.[TBA]3[H3PMo12O40][Zn4(L2)](2)[TPA]3[H3PMo12O40][Zn4(L1)]·0.5H2O(3).The dimer is further linked by tritopic ligand in a staggered ethane style to form a(3,6)-connected topology.2 has a window of-24 × 14 A in the ab plane.3 maintains microporous properties in the be plane,ac plane and ab plane with the channel dimensions of-10×6A,-7 ×4A and-12 × 5 A.After PLATON calculations,when no TPA ions occupying the pores,the pore structure accounts for 58.1%of the total volume.3.By using the methodology of extending the reduced transition-metal-grafted s-Keggin polyoxoanions with two H3L1 and H3L2,we isolated two polyoxometalate-based metal-organic frameworks,[TBA]9{[H3PMoⅤ8MOⅥ4O40]2[H2PMoⅤ4MoⅥ8O40]}[Zn12(Ll)4](4),[TBA]3[H4PMo12O40][Zn4(HL2)2]·0.5H2O(5)(H3L1=[1,1’;3’,1"-terphenyl]-3,5’,3"-tricarboxylic acid;HaL2 =[1,1’,3’,1"-terphenyl]-4,5’,4"-tricarboxylic acid;TBA = tetrabutylamonium).The combination of tetrahedral inorganic building blocks and rigid triangular organic linkers is expected to produce(3,4)-connected nets.To date,only three types of topologies of ctn,bor and ofp were identified.Interestingly,in this work,an unprecedented(3,4)-connected topology(labelled as yzu)was identified in compound 4,in which the 4-connected node of {Zn4-s-Keggin} maintains the tetrahedral extending and the LI ligand exerts the triangular linking role.However,under the influence of a 4-substitued ligand of H3L2,the 4-connected node of {Zn4-ε-Keggin} exhibits the distorted tetrahedral extending,as a result,a 2D network of 44 topology is formed in compound 5,in which the HL2 ligand acts as an angular linker.4.Due to the presence of POM anions,Compounds 1-5 exhibit excellent electrochemical activity.Then these compounds are made into modified glassy carbon electrodes(GCE).Experiments indicate that compounds 2-4 have high sensitivities of the electrochemical sensing to bromate.Moreover,it is expected that the entrapment of POMs in a 3D configuration could induce huge enhancement of their electrocatalytic activity.Therefore,compounds 2-4 were employed as electrocatalysts for the electrocatalytic reduction of bromate.