Synthesis And Catalytic Performances Of Vanadate-based Complexes Constructed By Bidentate Organic Amine Ligands

To construct polyoxometalate-based complexes with diverse structures and excellent catalytic properties,the organic compounds with bidentate coordination groups,ethylenediamine（en）and 3,5-di（1H-triazolyl-1-yl）benzonitrile（DTCN）,were chosen as organic ligands in the paper.Four vanadate-based complexes 1-4 have been successfully isolated.The structure of complexes 1-4 were characterized and described in detail.Additionally,the photocatalytic and electrocatalytic properties of the complexes have been researched.Moreover,the catalytic properties for oxidation of thioether compounds have also been studyed.1.Choosing the DTCN accompanying with bidentate N-proton coordination groups as organic ligand in the reaction system containing NH₄VO₃,two vanadate-based complexes1 and 2 have been synthesized under hydrothermal condition by tuning the metal ions,p H and ratio of raw materials,et al,with the help of the in situ ligand transformation.[Co（HDTBA）V₂O₆]（1）[Ni（H₂O）（DTBA）₂V₂O₄（OH）₂]·4H₂O（2）DTBA=3,5-di（1H-imidazol-1-yl）benzoic acidDuring the synthesis of complexes 1 and 2,the DTBA ligand was generated in situ from the hydrolysis of DTCN ligand.In the structure of complex 1,the tetranuclear vanadium oxygen clusters[V₄O₁₂]^4-were connected by Co²⁺ions in a kind of novel connection pattern,forming a two-dimensional Co-O-V layer.The N-donor groups of DTBA ligands linked these layers into a 3D framework structure.Complex 2 has a 2D structure.The binuclear vanadium oxygen clusters[V₂O₄（OH）₂]^2-modified by two DTBA ligands via sharing carboxylic oxygen atoms of the DTBA ligand were aggregated by Ni²⁺ions to yield the 2D layer of complex 2.The investigations on the properties indicated that complexes 1 and 2 have good electrocatalytic activities against the oxidation of ascorbic acid（AA）.Additionally,complex 1 under ultraviolet excitation,shows good catalytic activity for the degradation of gentian violet（CV）methylene blue（MB）.Meanwhile,complexes 1 and 2 have excellent catalytic activities for oxidation of thioether compounds with good stability and reusability as heterogeneous catalysts.2.Introducing ethanediamine as another bidentate ligand into the reaction system containing NH₄VO₃ and DTCN for constructing the vanadate-based complexes with novel architectures,two vanadate-based complexes 3 and 4 were prepared under hydrothermal condition by the addition of H₃PO₄ or Keggi-type polyoxoanion[PW₁₂O₄₀]^3-.（H₂en）₂（Hen）[V^Ⅲ（H₂O）₂（V^ⅣO）₈（OH）₄（HPO₄）₄（PO₄）₄（H₂O）₂]·2H₂O（3）[（H₂DTBA）₂](VW₁₂O₄₀)·2H₂O（4）In 3,the DTCN ligands were not transformed in stiu into the DTBA ligand,and absent in the final structure.But the coordination of ethanediamine,phosphate and vanadium oxygen clusters gave a new vanadate-based complex.Four{VO₄}and{PO₄}clusters were alternately connected to form a ring-like unit.Two adjacent rings were connected by sharing vertices to give a wave-like two-dimensional layer structure,further resulting in a 3D framework through the connection of{V（H₂O）₂}units.Complex 4 has a 3D supramolecular structure,in which not only the DTCN was transformed in situ into the DTBA ligand,but also the[PW₁₂O₄₀]^3-anion was transformed in situ into the[VW₁₂O₄₀]^4-anion.The study of catalytic performances showed that complex 3 had not only good photocatalytic activities for the degradation of CV,but catalytic property for oxidation of thioether compounds.Moreover,complex 4 displayed better photocatalytic activities for the degradation of MB and CV.