Syntheses, Structures And Properties Of Polyoxoniobates And Polyoxotantalates Compounds

Under appropriate conditions, six novel polyoxoniobates and two polyoxotantalates were prepared by the reaction of nitrogen-containing ligands, transition-metal cations and hexaniobates K₇HNb₆O₁₉·nH₂O or hexatantalates K₈Ta₆O₁₉·nH₂O, which were fully characterized by elemental analyses, X-ray powder diffraction (XRPD), IR spectroscopy, UV spectroscopy, electrochemical property, single-crystal X-ray diffraction analyses and thermogravimetric analyses.1. A series of novel organic–inorganic hybrids containing [Nb₁₀O₂₈]^6– building blocks [Ni(2,2′-bipy)₂]₃[Nb₁₀O₂₈]·2H₂O (1), [Ni(2,2′-bipy)₃]{[Ni(2,2′-bipy)₂]₂[Nb10 O28]}·8.5H₂O (2), [M(phen)₃]{[M(phen)₂]₂[Nb₁₀O₂₈]}·8H₂O (M = Ni^II for 3; M = Zn^II for 4; M = Co^II for 5) (2,2′-bipy = 2,2′-bipydine, phen = 1,10-phenanthroline) have been successfully synthesized using the hydrothermal method by introducing different transition-metal complexes. 1 is a one-dimensional (1D) infinite chain polyoxoniobate built by [Nb₁₀O₂₈]^6– units and [Ni(2,2′-bipy)₂]₃⁶⁺ cations. Furthermore, adjacent chains in 1 are further interacted byπ–πstacking interactions resulting to a three-dimensional (3D) supramolecular network. ^2–5 are constructed from [Nb₁₀O₂₈]^6– units and different transition-metal complexes, in which neighboring units are combined together via theπ–πinteractions between pyridine rings of ligands forming a 1D linear supramolecular chain.2. A new organic-inorganic hybrid polyoxoniobate [Cu(1,3-dap)₂(H₂O)][(H₆Nb₆O₁₉)₂ Cu(1,3-dap)₂]·4(1,3-dap)·20H₂O (6) (1,3-dap = 1,3-diaminopropane) has been synthesized by the diffusion method. Crystal structure analysis reveals that 6 consists of one dimeric dumbbell anion [(H₆Nb₆O₁₉)₂Cu(1,3-dap)₂]_<sup>2–, one copper coordinated cation, four 1,3-dap ligands and twenty crystal water molecules, in which the neighboring units are combined together via the hydrogen bonding interactions forming a 3D supramolecular framework.3. Two novel polyoxotantalates [K(H₂O)₄]₂[Cu(NH₃)₄(H₂O)]₂[Ta₆O₁₉] (7) and [Cu(NH₃)₅]₂[Cu(NH₃)₂]₂[Ta₆O₁₉]·8H₂O (8) have been succeessfully synthesized using the diffusion method. 7 and 8 represent the first two examples of inorganic coordinated compounds based on [Ta₆O₁₉]^8– polyoxoanion in POM field.