Synthesis and characterization of the water-soluble, all-inorganic composition, Keggin-type triniobium(V)-substituted SiW9Nb3O407- heteropolyoxoanions with alkali metal countercations (Li+, Na+, K+, and Cs+)

Article abstract of DOI:10.1246/bcsj.71.2603

The Keggin-type triniobium(V)-substituted tungstoheteropolyanion, A-β- SiW₉Nb₃O₄₀^7-, was synthesized as its hepta alkali-metal salts of Li⁺, Na⁺, K⁺, and Cs⁺ countercations. These alkali-metal salts were useful for allowing the crystallization of SiW₉Nb₃O₄₀^7-, itself, and/or the SiW₉Nb₃O₄₀^7--supported organometallic complexes, as well as controlling the water solubility of these complexes. The analytically pure compounds, obtained as homogeneous colorless solids via a stoichiometric reaction of the (Bu₄N)₆H₂Si₂W₁₈Nb₆O₇₇, (Nb-O-Nb)₃-bridged anhydride with the corresponding alkali tetrafluoroborates and then with the alkali hydroxides, were compositionally characterized by complete elemental analyses, TG/DTA and FABMS spectra. They were structurally characterized by FT-IR and solution ¹⁸³W NMR measurements, as well as solid-state CP/MAS and GHD/MAS ²⁹Si NMR and solution ²⁹Si NMR measurements. The cation-dependent properties of these heteropolytungstates in the solid state were observed in the thermal stabilities, the amounts of hydrated water and adsorbed water, the solubilities in water and in organic solvents, and in the ease of crystallization.