SYNTHESIS AND CHARACTERIZATION OF WATER-SOLUBLE, ALL-INORGANIC COMPOSITION, DAWSON-TYPE TRISUBSTITUTED HETEROPOLYTUNGSTATES - EFFECT OF ALKALI-METAL COUNTERCATIONS (LI, NA, K, AND CS) ON THE P2W15NB3O629- POLYOXOANION

The water-soluble form of the Dawson-type trisubstituted tungstohetero polyanion, B-alpha-P2W15Nb3O629-, was synthesized as its nona alkali-m etal salts of Li, K, and Cs. Analytically pure compounds, obtained as homogeneous colorless solids, had nonahydrate for the nonalithium (Li- 9) salt, tetrahydrate for the nonasodium (Na-9) salt, trihydrate for t he nonapotassium (K-9) salt and trihydrate for the nonacaesium (Cs-9) salt, respectively, after each was dried overnight at room temperature under 10(-3)-10(-4) Torr. TG/DTA analyses show that they can be made with 25 water for the Li-9 salt, 23 water for the Na-9 salt, 9 water f or the K-9 salt, and 8 water for the Cs-9 salt under atmospheric condi tions. A compositional characterization was accomplished by complete e lemental analyses and TG/DTA, and structural characterization was achi eved by a combination of FT-IR and variable-temperature solid-state P- 31 NMR and by both P-31 and W-183 NMR measurements at room temperature in D2O and DMSO-d(6) solutions. The amount of hydrated waters, solubi lity in solvents and ease of crystallization were significantly influe nced by the alkali-metal countercations. These cation-dependent proper ties are useful for selecting polyoxoanion precursor favorable to the crystallization of P2W15Nb3O629- supported organometallic complexes. T he effects of the cations (li, K, Na, and Cs) on the P2W15Nb3O629- wer e observed as different hydrated structures of the polyoxoanion and it s cation-dependent thermal stability in the solid state by a combinati on of TG/DTA and FT-IR measurements, and also as a spectral change of the downfiled P-31 Signal due to interactions of the polyoxoanion with the countercations and/or with hydrated waters by variable temperatur e (VT) solid-state GHD/MAS (PNMR)-P-31 spectroscopy.