Die Kristallstruktur des Dinatrium-oktammonium-parawolframat-dodekahydrats, Na2(NH4)8[H2W12O42] · 12H2O*

Abstract

Na₂(NH₄)₈[H₂W₁₂O₄₂] · 12H₂O crystallizes in space group Pbca, a = 15.78, b = 22.93, c = 14.13 Å, Z = 4, D _m = 4.12, D _x = 4.27 g · cm⁻³. The W atoms were located by a Patterson map, the lighter atoms (21 O, 1 Na, 4 NH₄, 6 H₂O) by a ΔF map. Using anisotropic temperature factors for W and isotropic ones for the other atoms, the structure was refined to R = 9.0% for 3069 reflections, 772 of which were unobserved (122 of these had F _o > F _min). The anion [H₂W₁₂O₄₂]¹⁰⁻ is built up by four groups of three edge-sharing octahedra each. It exhibits 2/m pseudosymmetry (W–O = 1.96 Å). The Na atom is octahedrally surrounded by two O and 4 H₂O (Na–O = 2.39 Å). The cations are bound to the polyanion at about the same sites as in ammonium paratungstate decahydrate and tetrahydrate.