Structure d'un paratungstate d'ammonium (NH₄)₆H₆W₁₂O₄₂.10H₂O

Structure of potassium paradodecatungstate 71/2-hydrate

“…These have been found by crystal structure analysis to be a paradodecatungstate salt, K Io[H2WI2042 ].7~H20. The structure turned out to be closely isotypic with the previously reported structure of (NH4)6H6W12-O42.10H20 (Averbuch-Pouchot, Tordjman, Durif & Guitel, 1979), indicating that the chemistry of the latter needs to be revised.…”

“…The numbering of atoms in the molecules (Fig. 1) When the potassium paradodecatungstate structure is compared with that of the ammonium salt (NHa)6H6WI2Oa2.10H20, whose structure was reported by Averbuch-Pouchot et al (1979), the unit-cell parameters are found to be similar within 2% (Table 1). Furthermore, nearly all the atomic coordinates, after suitable transformation, are closely analogous.…”

“…Furthermore, nearly all the atomic coordinates, after suitable transformation, are closely analogous. The main difference lies in the number of counterions present: Averbuch-Pouchot et al (1979) found six NH4 + ions and postulated the presence of four H + ions to balance the charge of the polyanion…”

“…The four additional K + ions in this crystal correspond to four of the water molecules reported for the ammonium compound. Since it is not possible in structures of this type (dominated by the heavy W scatterers) to distinguish between N and O atoms, it must be concluded that Averbuch-Pouchot et al (1979) misidentified four of the NH4 groups as H20 molecules. When this substitution is made a much more even distribution of counterions around the polyanions is found.…”

“…Every atom listed for the ammonium compound by Averbuch-Pouchot et al (1979) corresponds to an atom in the K compound except for O(W10), which could not be found in the electron density map of the K salt. Rather, five additional peaks were found which are labeled Aq(6), Aq(7a,b) and Aq(Sa,b).…”