Synthesis And Characterization Of Novel Polyvanadoxycluster Compounds

Polyoxovanadates are an extremely important branch of polyoxomatalates,with wide structural variety and potential applications in different areas,such as catalysis,photoelectric and magnetic aspects.Therefore,polyoxovanadates have attracted a great deal of attention by researchers.Polyoxovanadates are synthesized under high temperature solid phase or hydrothermal conditions.In recent years,people try to introduce heteroelements into vanadate system to form more abundant crystal structure of substituted vanadates.The boron atom usually uses the BO3 triangle structure with three oxygen atoms coordination or the BO4 tetrahedron structure with four oxygen atoms coordination as the main building unit.They can join to form various boroxy clusters by sharing oxygen atoms.These[BxOy]clusters can be integrated into the[VxOy]n-framework of vanadium oxide polyanion to produce polyoxovanadium borates crystals with novel structure.The different connections of[VOx](x=4,5,6)and[BOx](x=3,4)polyhedral units eventually lead to a variety of structural types of polyoxovanadium borates anion clusters.At the same time,Ge also has a variety of coordination structure types:the[GeO4]group with four oxygen atoms coordination in a tetrahedral geometric configuration,the[GeO5]group with five oxygen atoms coordination in a triangular biconical or tetragonal pyramid geometric configuration,and the[GeO6]group with six oxygen atoms coordination in an octahedral geometric configuration.These germanium oxygen polyhedral groups can replace the vanadium atoms on the[V18O42]cluster to form vanadium germanate with more diverse structural types.Our research group is trying to incluse heteroelementa in to the polyoxovanadate backbones.On the basis of previous studies,a series of vanadate compounds were synthesized and characterized by single crystal X-ray diffraction,powder X-ray diffraction,FTIR spectroscopy,thermogravimetric analysis and elemental analysis.We classify the synthesized compounds into two categories:1.Vanadogermanate.A case of vanadium germanate was synthesized by hydrothermal and solvothermal methods:[Zn(en)(H2O)Zn(dien)Zn(en)2]2[Ge6V15O48]·(en)2(H2O)10(2-1)(en=ethylenediamine)Compound 2-1 contains a spherical[V15Ge6]cluster,which can be discribed as three[VO5]tetragonal pyramids of the[V18O42]cluster replaced by three[Ge2O7]dimers.[V15Ge6]clusters are further connected by Zn-complexes to two-dimensional networks.2.Vanadoborates.Four vanadoborates are synthesis by solvothermal method:[Na3(H2O)4][V12B18054(OH)6]·2H2O(3-1)[(CH3)2NH]3[(CH3)2NH2]4{V10B24O58(OH)4[(CH3)2NH]4}·3H2O(3-2)(dap)(H2dap)6[V10B26O62(OH)6(dap)2]·2B(OH)3·2H2O(3-3)(dap=1,3-propyleneamine)(H2dab)4[Cd2(dab)(Hdab)4V10B24O58(OH)8](3-4)(dab=1,4-butanediamine)Compound 3-1 contains[V12B18]cluster,which is composed of a[B18O42]ring sandwiched in-between two[V6O18]fragments.Six[VO5]are connected via edge-sharing yielding a[V6O18]unit.[V12B18]clusters are connected by[NaOx]polyhedral into three-dimensional framework.All the compounds 3-2,3-3 and 3-4 contain a[V10B20+x]cluster.In compound 3-2,two crown-like[B12O26]are connected to the upper and lower sides of[(O=VO2)10]cluster,and two dimethylamine molecules are connected to borate clusters through B-N bonds.In compound 3-3,a[B13O29]cluster is connected to the upper and lower sides of[(O=VO2)10]polyanions and each of the two ten-membered rings is linked to a 1,3-propylene diamine molecule.Similar with 3-2,the upper and lower sides of the V10 cluster in compound 3-4 are respectively connected to[B12O26].Different from compound 3-2,the organic amine molecule is not directly connected to the cluster,but to the second transition metal Cd.Each Cd atom is five-coordinated with three N atoms from three 1,4-butylene diamine molecules respectively,and two oxygen atoms from the borate clusters.