The Ag2O-V2O5-HF(aq) system and crystal structure of α-Ag3VO4

Reactions between the three components Ag2O, V2O5, and HF(aq) were investigated under hydrothermal conditions, and the recovered phases were, in increasing Ag:V content, Ag2V4O11, beta-AgVO3, Ag4V2O6F2, Ag4V2O7, and alpha-Ag3VO4. A higher ratio of Ag2O to V2O5, as compared to a stoichiometric ratio, was required to synthesize Ag4V2O6F2, Ag4V2O7, and alpha-Ag3VO4. Owing to their solubility differences, the crystallization regions are not centered around the respective 2:1 and 3:1 Ag2O/V2O5 tie-lines but rather are centered along the 4:1 and 8:1 Ag2O/V2O5 tie-lines. Reactions with a 4:1 Ag/V ratio either resulted in Ag4V2O6F2 at 150 degrees C or Ag4V2O7 at 200 degrees C. Products were recovered in between 80% and 100% yield based on V2O5. Red transparent crystals of alpha-Ag3VO4 crystallize in the monoclinic space group C2/c, with cell parameters a = 10.1885(16) angstrom, b = 4.9751(8) angstrom, c = 10.2014(17) A, beta = 115.754(3)degrees.