Synthesis And Structural Chemistry Of Polyoxovanadium Borate Clusters

Polyoxovanadium borate is a new field of polyoxometalate chemistry. The coordination geometries of V and 0 contain VO6 octahedron, VO5 square pyramid and VO4 tetrahedron. The coordination geometries of B and O contain BO4 tetrahedron, BO3 triangle; and many structures are based on them. The various connection modes between V-O polyhedron and B-O polyhedron allow polyoxovanadium borates to be structurally very diverse.We carried out the study about hydrothermal synthesis of polyoxovanadium borates and intended to find the relationship between properties and structures based on summary of literature search systematically. So far we had made achievements on such aspect:1. Devising and synthesizing ten novel polyoxometalates and employing X-ray single crystal diffractometer technology to determine their structures:(enH2)6H3[(VO)12O6B,8O42]-13H20 1(cnH2)5H5[(VO)12O6BisO42]-9.25H2O 2[Ni(en)2]6H3[(VO)12O6B18O42]-8H2O 3[Co(cn)2]6H3[(VO)12O6B,gO42]-10H2O 4|Ni(TI-ATA)]6H3[(VO),2O6B18O219H2O 5[Cu(cn)2]5H3[(VO)l2OJ318042][B(OH)3]2-16H2O 6Na2II7[(VO)|2O6{B3O6(OH)}6]-22H2O 8Na7175H1.825[(VO)12O6{B3O6(OH)}6]-15H2O 9Hio[NiMov,2O4o{Ni(H2O)3}4] ]0Among these compounds, compound 1_ and 2 possess [V12B18O60] frameworks, winch consists of an IS-membcred ring of Bi8O42 sandwiched between two alternating edge-sharing vanadium-oxygen clusters V60is, respectively. Compound 3 ~5 possess [MN4]6[V|2B18O60] frameworks. They are a kind of novel polyoxovanadium boratcs in which [MN.i] connected with [V12B18O60] by the bridging oxygens of B18O42 ring. In compound 6, the [V12B18O60] clusters are connected with [Cu(en)2] by terminal oxygens, and then the compound was extended an infinite two-dimensional network structure. In compound 7-9, the [V12B18O60] clusters are connected with Na+. Compound 7 and 8 was extended an infinite two-dimensional network structure and compound 9 consists of isolated clusters. The structure of compound W contains a e-Kcggin core whose center is a NiO4 tetrahedron and which is capped with four NiO6 octahedrons. All ten polyoxomctalates display complicated hj'drogen bonds.2. Employing IR, Raman, DRS, fluorescent spectra and TGA to characterize some compounds. Some instructive and interesting results can be obtained after the discussion dspeclroscopy in details. In IR and Raman spectra, we ascribed the characteristic peaks oi polyo.xoinetalates to corresponding vibration frequencies and found the characteristic peaks are related to the bond length between metals and oxygens, the coordination surroundings , hydrogen bonds and so on. In UV-Vis DRIS spectra, the LMCT bands of Ot →M are found at about 205nm and the LMCT bands of Ot→M split into two peaks. The fluorescent spectra of some solid compounds were obtained by the excitedwavelength is 220nm or above 300nm. The fluorescent lifetime results show that these compounds have one or two kinds of luminous group. At last, from TGA diagram of compound 1 and 6 we find the fact that with the rise of temperature, compounds have two ranges of weight losing, corresponded to the lose of crystal waters and organic molecules respectively. The [V12B18O60] cluster exists stably below 500℃.3. Performing thel energy calculation of the system: [(VO) 1 2658 1 3642] I5~ and {[Ni(NH3)2]6[(VO)12O6B18O42]}3- by using the quantum chemistry method. We obtained their reactive centers based on the calculated net charge. In [(VO)12O6B18O42]15- anion cluster, μ 2-O and Ot are the reactive centers in nucleophilic reaction. So they are easy to be hydrogen bond or to be attacked by metallic cations. The structures of compound 1 to 9 show the mode of this bond. In these two anion clusters, μ 3-O is the activity centers catalysis.