1998 Volume 71 Issue 11 Pages 2603-2610
The Keggin-type triniobium(V)-substituted tungstoheteropolyanion, A-β-SiW9Nb3O407−, 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−-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.
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