Synthesis,Structure,and Electrochemistry Properties Of Polyoxometalate-materials Containing Nitrogen Ligands

Polyoxometalates?POMs?have been receiving considerable attention owing to their excellent optical,magnetic,catalytic characteristics and unique electrochemistry properties.Studying the effect of POMs coordination modes on electrochemical activities would be of great significance for constructing POM materials with extraordinary performance.In this paper,three new POM compounds were obtained by solvothermal technique using nitrogen-containing ligand 4,4'-bis?imidazolyl?biphenyl?bibp?and silicotungstic acid(H₄SiW₁₂O₄₀)when controlling the reaction conditions:{[Cd?DMA?₄]₂?bibp?(SiW₁₂O₄₀)}_n?1?{Cd₂?bibp?_2.5?DMA?₅(SiW₁₂O₄₀)}_n?2?{Cd?bibp?₂?DMA?₂}_2n(SiW₁₂O₄₀)_n·3nDMA?3?The single crystals were cultured by adjusting the reaction environment.The structures and properties were characterized by X-ray single crystal analysis,elemental analysis,IR spectra analysis,X-ray powder diffraction analysis,thermogravimetric analysis,and electrochemical analysis.Structural analyses reveal that compounds 1-3 are roughly identical in chemical composition,which are composed of[SiW₁₂O₄₀]^4-anions,bibp ligands,Cd²⁺ions,and solvent molecules DMA.However,their structures and the coordination modes of POMs are different.Compound 1 exhibits a one-dimensional?1D?chain structure.The[SiW₁₂O₄₀]^4-anions and bibp ligands are linked by Cd²⁺ions alternately into a zigzag-like chain.Compound 2 is of two-dimensional?2D?layer structure.The Cd²⁺ions and bibp ligands are linked into chains,and[SiW₁₂O₄₀]^4-anions connect the chains into layers.Compound 3 displays 2D host-guest structure.The 2D host framework is constructed by Cd²⁺ions and bibp ligands.The host and[SiW₁₂O₄₀]^4-anions guest are connected through hydrogen bonds to form a sandwich-type layered structure.Compounds 1-3 exhibit several structural types,metal ions,organic ligands and POMs with or without chemical bonds.In compounds 1 and 2,metal ions,organic ligands engraft onto POMs via Cd-O bond;In compound 3,POMs and metal-organic frameworks interact to build 2D host-guest structure through hydrogen bonds.Electrochemical studies show that there are redox processes centered on W atoms for the three compounds,and that the three compounds have electrocatalytic activity for the reduction of nitrite and exhibit high electrocatalytic efficiency?CAT?.The analysis shows that the CAT of compounds 1 and 2 which POMs engraft onto the framework are relatively high,and the CAT of compound 3 with POMs as a guest is relatively low.The study shows that the electrochemical properties of POM are affected easily by coordination modes,and the electrocatalytic activity of POM materials can be improved by adjusting the coordination modes of POMs.