Selenoarsenate aus wäßriger Lösung. Die Kristallstruktur von Na3AsO3Se · 12 H2O und Na3AsSe4 · 9H2O

Selenoarsenates from Aqueous Solutions. Crystal Structures of Na₃AsO₃Se · 12 H₂O and Na₃AsSe₄ · 9 H₂O Selenoarsenates are obtained from aqueous solutions as colourless hydrated salts by reactions either of As₂O₃ with NaOH and selenium or of Na₂Se with As₂Se₃ and selenium under strictly anaerobic conditions. Besides of tetrahedral anions AsO₃Se^3? and AsSe₄^3?, extensive hydrogen bridge systems with rather strong O? H …?s Se bonds determine the structures. Na₃AsO₃Se · 12 H₂O is orthorhombic (P2₁2₁2₁) with a = 9.220(3), b = 13.018(3), c = 14.048(4) Å, Z = 4. Cubic Na₃AsSe₄ ·s 9H₂O (P2₁3) with a = 12.149(3) Å is isotypic to Schlippe's salt, Na₃SbS₄ · 9 H₂O. The full X-ray structure analyses from four-circle diffractometer data show the selenium atoms of the AsO₃Se^3? and AsSe₄^3? anions to be H-acceptors in six Se …? H? O hydrogen bridges with d(Se …? O) = 3.357–3.693 Å and d(Se …? H) = 2.47–2.89 Å. The As? Se bond in AsO₃Se^3? (2.283 Å) is shorter than in AsSe₄^3? (2.319 Å).