Synthesis and characterization of tri-titanium(IV)-1,2,3-substituted alpha-Keggin polyoxotungstates with heteroatoms P and Si. Crystal structure of the dimeric, Ti-O-Ti bridged anhydride form K(10)H2[alpha,alpha-P2W18Ti6O77]center dot 17H(2)O and confirmation of dimeric forms in aqueous solution byultracentrifugation molecular weight measurements

The preparation and characterization of the alpha -Keggin-type, novel tri-T i-IV-1,2,3-substituted polyoxotungstates with heteroatoms P and Si are desc ribed. The molecular structure of K10H2[alpha,alpha -P2W18Ti6O77]. 17H(2)O 1, obtained as a main product (30.4% yield) from the 1:3 molar ratio reacti on of tri-lacunary precursor Na-9[A-PW9O34]. 19H(2)O with Ti(SO4)(2). 4H(2) O in aqueous solution, was determined by X-ray structure analysis. It had t he dimeric, anhydride structure formed by three Ti-O-Ti bonds linking two K eggin [alpha -1,2,3-PW9Ti3O40](9-) units. From the filtrate after 1 was fil tered off, a different compound 2 was obtained as a minor product. A relate d alpha -Keggin tri-Ti-IV-1,2,3-substituted polyoxotungstate with heteroato m Si, the dimeric anhydride form K10H4[alpha,alpha -Si2W18Ti6O77]. 15H(2)O 3, was obtained as a main product (31.1% yield) from a 1:3 molar ratio reac tion of Na-10[A-alpha -SiW9O34]. 15H(2)O with Ti(SO4)(2). Ultracentrifugati on molecular weight measurements under less acidic conditions revealed that I bind 3 were present as dimers in aqueous solution. Characterization of I and 3 was also accomplished by complete elemental analyses, TG/DTA, FTIR a nd solution (P-31 and W-183) NMR spectroscopies.