| Polyoxoniobates have attracted the attention of chemical researchers due to a wide range of value in photocatalytic hydrogen production,base catalytic organic reactions,nuclear waste treatment,antitumor and magnetism fields.However,the development of polyoxoniobates is slower than that of polyoxotungstates,polyoxomolybdates and polyoxovanadates owing to the specific alkaline synthesis condition.Introducing transition-metals into polyoxoniobates is one of the effective ways to construct novel multi-functional polyoxoniobates,but many transition-metal ions are liable to form precipitates under alkaline conditions.The complexation of transition-metal ions and protective ligands is a breakthrough point to construct novel transition-metal modified polyoxoniobates.The research of polyoxoniobates with transition-metals and organic amine ligands as linking units is of great significance for the development of polyoxoniobates.In this paper,two transition-metals(nickel or copper)modified dicapped Keggin polyoxovanadoniobates were obtained in high yields under solvothermal by using glycol and water as mixed solvents and selecting the precursors K7HNb6O19·13H2O,transition-metal salts(nickel or copper salts),metavanadates and organic amines(ethylenediamine)as raw materials.The resulting compounds were characterized by X-ray single crystal diffraction,Elemental analysis,PXRD,XPS,IR,TG,and their performance in catalyzing the cyanosilylation reaction of aldehydes/ketones with trimethylsilyl cyanide has been investigated.H[Ni(en)3]5[VNb12O40(VO)2]·15H2O(1)H3[Cu(en)2]4[VNb12O40(VO)2]·13H2O(2)In compound 1,each polyoxoniobate anion[VNb12O40(VO)2]11-is surrounded by five octahedral configuration[Ni(en)3]2+.[Ni(en)3]2+and[VNb12O40(VO)2]11-are connected by electrostatic attraction and hydrogen bonding interaction,forming a 3D supramolecular structure.In compound 2,each polyoxoniobate anion[VNb12O40(VO)2]11-is coordinated with eight planar quadrilateral[Cu(en)2]2+by Nb?O···Cu.Each[Cu(en)2]2+as a bridging group interacts with adjacent two polyoxoniobate anions[VNb12O40(VO)2]11-,forming a 3D network structure.Due to the synergy between highly negative polyoxoniobate anions and transition-metal chelates,compounds 1 and 2 showed remarkable catalytic performance for cyanosilylation of various aldehydes/ketones,giving the corresponding cyanohydrin trimethylsilyl ethers with high yields in short time.The Lewis basicity of polyoxoniobate anions in compounds 1 and 2 plays a major role for this catalytic reaction.The catalytic activity of compounds 1 and 2 did not decrease significantly after several cycles of catalytic reactions. |
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