Synthesis of Silver Tetratungstate

Submitted by S. A. WILBER, S. GELLER, and G. F. RUSE Checked by G. LUNDt 

Syntheses of Ag2W04 have been reported elsewhere.4-6 However, even in a very recently published paper6 dealing with the solubility of this material, the authors did not realize that two different phases may be obtained depending on the pH of the reaction mixture and that the anionic unit in the solid phase is the tetramer. 

Adjustment of pH is important. Silver tungstate is also photosensitive to some extent thus to obtain a white product, the procedure is carried out under safe-light. 

Solution A is slowly added to solution B in a 3-L beaker with vigorous stirring. A heavy, pale yellow precipitate is formed. One liter of distilled water is added with stirring. The beaker and its contents are heated on a hot plate for about 20 min until the temperature reaches 40-50° the contents are stirred occasionally during the heating. 

Dilute (1 N) NH4OH is added until the pH is 5.5-6.0. If pH 6 is exceeded, dilute (1 N) HN03 is added to bring it back to between 5.5 and 6.0. WARNING If the pH exceeds 8.0, insoluble compounds may form. 

It has been shown that the anion in at least the high-temperature form of silver tungstate is [W40i6] therefore, its formula should be written Agg[W40i6] (not Ag2W04). Although the crystal structure of the low-temperature form has 

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