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+)

The Keggin-type triniobium(V)-substituted tungstoheteropolyanion, A-beta-Si W9Nb3O407-, 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 SiW9Nb3O407-, itself, and/or the SiW9Nb3O407--suppo rted organometallic complexes, as well as controlling the water solubility of these complexes. The analytically pure compounds, obtained as homogeneou s colorless solids via a stoichiometric reaction of the (Bu4N)(6)H2Si2W18Nb 6O77, (Nb-O-Nb)(3)-bridged anhydride with the corresponding alkali tetraflu oroborates, and then with the alkali hydroxides, were compositionally chara cterized by complete elemental analyses, TG/DTA and FABMS spectra. They wer e structurally characterized by FT-IR and solution W-183 NMR measurements, as well as solid-state CP/MAS and GHD/MAS Si-29 NMR and solution (29) Si NM R measurements. The cation-dependent properties of these heteropolytungstat es in the solid state were observed in the thermal stabilities, the amounts of hydrated water and adsorbed water, the solubilities in water and in org anic solvents, and in the ease of crystallization.