Syntheses,Structures And Properties Of New Type Polyoxoniobates

The thesis focuses on the synthesis of new type polyoxonibates（PONs）. It can be divided into two parts. By summarizing the ideas in the referances, we adopt the combination of hydrothermal and diffusion method. In the thesis, ten novel PONs have been successfully synthesized by using simple reactants. These complexes were further charactered by single-crystal X-ray diffraction, spectroscopic properties, thermogravimetric analyses, electrospray ionization mass spectrometry and magnetic properties. The assembly and derivatization conditions of these PONs were researched.I. Using K7HNb₆O₁₉·13H₂O, organic ligands and transition metals（TMs）, four novel TMcontaining PONs have been successfully synthesized by the combination of hydrothermal and diffusion method.1. A novel octacobalt-containing PON, Na₆K₁₂[H₂Co₈O₄(Nb₆O₁₉)₄]·39H₂O（1）, has been isolated. This is the first mixed-valence cobalt aggregate in PON chemistry. The overall architecture can be considered an octanuclear {Co8} cluster stabilized by four classical [Nb₆O₁₉]8– building blocks. The CoIII ions form distorted CoO6 octahedra whereas the oxidation state of the tetracoordinated cobalt is +2. Besides, magnetic measurements show that 1 exhibits antiferromagnetic behavior.2. We present a novel 10-nickel K₁₄Na₆[H₄Ni₁₀（H₂O）₈Nb₃₂O₁₀₂]·73H₂O（2）. Compound 2 is the highest-nuclearity, discrete, deca-nickel-containing PON. The polyanion consists of two [{Ni2O4}（H₂O）₂(Nb₆O₁₉)]12–（A） and two [Ni3（H₂O）₂Nb10O34]12–（B） subunits. The arrangement of all four fragments with respect to each other can be described as a rhomb-like structure. The A unit is derived from well-known [Nb₆O₁₉]8– on which is grafted two Ni ions via three adjacent bridging oxygen atoms. B is composed of a trinuclear moiety {Ni3O14} sandwiched by two lacunary Lindqvist [Nb5O18]11–.3. Two new TM-linked PONs based on Lindqvist [Nb₆O₁₉]8-, K₁₀[(Nb₆O₁₉)Cr^III（H₂O）₂]₂·28H₂O（3） and K₅[H₂AgNb₆O₁₉]·11H₂O（4）, have been synthesized by a new two-pot synthesis strategy. The polyanion of 3 can be considered as a dimers formed by two [(Nb₆O₁₉)Cr（H₂O）₂]5- subunits. More interestingly, [(Nb₆O₁₉)Cr（H₂O）₂]5- can be viewed as a {CrO6} octahedron single crowned in [Nb₆O₁₉]8-. The polyanion of 4 can be considered as an {Ag O6} triangular prismsingle crowned in [Nb₆O₁₉]8-. Further, both 3 and 4 exhibit photocatalytic H2 evolution activity.II. By carefully selecting the heteroanion templates, six novel heteropolyniobates have been successfully synthesized.4. A new heteropolyniobate, K_4.5（H₂en）₂H_5.5[FeNb₂₇O₇₆]·16H₂O（5）, has been synthesized. The polyoxoanion is a Fe-centered Nb/O cage which is composed of Keggin-type {FeNb12}（A） and a ringlike {Nb15}（B）. A is embedded in B, resulting in an assembly with idealized C3 v symmetry. As we known, Compound 5 is the largest example of containing Fe atom in polyniobates chemistry.5. A hexa-Nb-sandwiched heteropolyniobate was synthesized. The polyoxoanion [H₂Te₂Nb₂₄O₇₂]14–consists of two B-α-[TeNb9O33]17– subunits and a central distorted ring [Nb6O24]18–. Further, the catalytic study reveals that the hybrid material exhibits activity for the degradation of basic fuchsin.6. A novel heart-type niobictellurate aggregate has been successfully obtained. The polyoxoanion, [H₇Te₂Nb₁₉O₆₀]10, consists of four triad of {NbO6} octahedra. Four {Nb3O10} clusters contect together via two {TeO3} fragments, two {Nb3O16} units and a {Nb3O13} unit, respectively.7. A novel crescent-type tellurium-containing polyoxonibate is synthesized by hydrothermal method and diffusion method. The polyoxoanion can be seen as two {TeNb9} subunits connected by a tetragonal pyramid {Nb6O5} unit.8. Two new compounds, [Cu（en）₂（H₂O）][{Cu（en）₂（H₂O）}₂{Cu（en）₂}(HAs₃Nb₁₂O₄₀)]·13H₂O（9） and [Ni（en）₃]₄[HAs₃Nb₁₂O₄₀]·12H₂O（10）, have been synthesized and characterized by infrared spectrum and X-ray diffraction. The [As3Nb12O40]9– polyanion can be regarded as a decorated Keggin cluster with one arsenic atom as the heteroatom center and two arsenic atoms capping two opposite pits. The caps are formed by the ligation of the oxygen atoms on the two opposite {Nb4O4} faces to each As atom. The difference between them is the counter ion.