Synthesis And Performances Of Dawson-type Ta/W Mixed Polyoxometalates Derivatives

Because polyoxotantalates can only exist stably under strong alkaline conditions,it has been developing slowly for several decades.However,Ta/W mixed heteropoly acid can exist stably under acidic conditions,and is the breakthrough point for the development of Ta containing polyoxometalates.Therefore,it is of great significance to study the development of Ta/W mixed polyoxometalates for the development of Ta containing polyoxometalates..We herein report the self-assembly of Ta/W mixed-addendum POMs and Rare-earth ions in acid solution,which results in a series of RE-POMs.These complexes constructed by the Ta/W POMs{P₂W₁₅Ta₃O₆₂}and Rare-earth ions,which are linked via RE-O-Ta bridges.Fourteen compounds were synthesized:[La?H₂O?₂₂]P₂W₁₅Ta₃O₆₂·16H₂O?1?[Ce?H₂O?₂₂]P₂W₁₅Ta₃O₆₂·16H₂O?2?[Pr?H₂O?₂₂]P₂W₁₅Ta₃O₆₂·16H₂O?3?[Nd?H₂O?₂₂]P₂W₁₅Ta₃O₆₂·17H₂O?4?[Y?H₂O?₇]₃P₂W₁₅Ta₃O₆₂·27H₂O?5?[Eu?H₂O?₇]₃P₂W₁₅Ta₃O₆₂·26H₂O?6?[Gd?H₂O?₇]₃P₂W₁₅Ta₃O₆₂·25H₂O?7?[Tb?H₂O?₇]₃P₂W₁₅Ta₃O₆₂·26H₂O?8?[Dy?H₂O?₇]₃P₂W₁₅Ta₃O₆₂·25H₂O?9?[Ho?H₂O?₇]₃P₂W₁₅Ta₃O₆₂·25H₂O?10?[Er?H₂O?₇]₃P₂W₁₅Ta₃O₆₂·26H₂O?11?[Tm?H₂O?₇]₃P₂W₁₅Ta₃O₆₂·26H₂O?12?[Yb?H₂O?₇]₃P₂W₁₅Ta₃O₆₂·26H₂O?13?[Lu?H₂O?₇]₃P₂W₁₅Ta₃O₆₂·25H₂O?14?Compounds 1-4 are 1D infinite chain.The molecular chains connect to each other through abundant hydrogen-bond interactions forming a 3D structure.They showed excellent proton conduction performance at high relative humidities?RHs?,with conductivity reached to 1.26×10^-2 S·cm^-1 at 95°C under 98%of RH.Compounds 5-14 are zero dimension monomers.These monomers were synthesized with high yields by single-step reaction procedures under mild reaction conditions.The simple and controllable synthetic method of the monomers compounds made it possible to rapid preparation of nanocrystal samples in large scale.These compounds are all electroneutral clusters;hardly soluble in water and insoluble in common organic solvent.They exhibit interesting electrochemical behavior and high catalytic activity for the Cyanosilylation as heterogeneous catalyst.A new HPAs H₂₀[P₈W₆₀Ta₁₂?H₂O?₄?OH?₈O₂₃₆]·125H₂O?H-1?which comprises a Ta/W mixed addenda heteropolyanion,20 protons,and 125 crystalline water molecules has been prepared through ion-exchange method.The structure and properties of H-1 have been explored in detail.AC impedance measurements indicate that H-1 is a good solid state proton conducting material at room temperature with a conductivity value of 7.2×10^-3 S·cm^-1?25°C,30%RH?.Cyclic voltammograms of H-1 indicate the electrocatalytic activity towards the reduction of nitrite.Hammett acidity constant H₀ of H-1 in CH₃CN is-2.91,which is the strongest among the present known HPAs.Relatively,H-1 exhibits excellent catalytic activities toward acetal reaction.