Tetrabutylammonium Hexatungstate VI

This polyoxoanion is prepared according to the procedure previously described for the hexamolybdate.  

All reagents are commercial analyzed reagents, used without further purification. 

A mixture of 33.0 g (100 mmol) of sodium tungstate dihydrate (Na2W04 2H20, 99%), 40 mL of acetic anhydride, and 30 mL of N,N-dimethylformamide(DMF) is stirred, in a 250-mL Erlenmeyer flask, at 100°C for 3 h. A white fluid cream is obtained. 

A solution of 20 mL of acetic anhydride and 18 mL of 12 N HCl in 50 mL of DMF is added with stirring, and the resulting mixture is gravity filtered through a medium porosity filter paper in order to eliminate the undissolved white solid. After washing the solid with 50 mL of methanol, the clear filtrate is allowed to cool to room temperature. A solution of 15 g (47 mmol) of tetra-butylammonium bromide in 50 mL of methanol is added with rapid stirring, to give a white precipitate. This suspension is stirred for 5 min and the product 

Recrystallization from a minimum amount of hot dimethyl sulfoxide (DMSO) (8mL, 80°C) gives, after 2 days at room temperature, 18 g of clear colorless diamond-shaped crystals, which are collected on a Pyrex Buchner funnel with fritted disk (porosity 5-15/i), using suction. Yield 18 g (10 mmol), 60% of theory based on W. 

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