Datensatz

Zusammenfassung

SeO2 and As2O3 were reacted at 200 degrees C in in a potassium hydroxide hydroflux with a molar water-base ratio n(H2O) : n(KOH)=1.8. Arsenate(III) disproportionates under these conditions into arsenate(V) and elemental arsenic. The reduction also yielded tetraselenodiarsenate(II) anions, which turned the solution yellow and precipitated at room temperature as plate-shaped crystals of K-4(As2Se4) . 2H(2)O. The unexpected redox reaction as well as the formation of a hygroscopic compound in an aqueous solution are attributed to a strongly reduced activity of water in ultra-alkaline media. K-4(As2Se4) . 2H(2)O crystallizes in the orthorhombic space group Cmce with lattice parameters a=784.78(3), b=1027.76(4) and c=1750.63(7) pm at 100 K. The (As2Se4)(4-) anion has C-2h symmetry and an As-As bond length of 245.3(1) pm. The water molecules are part of infinite zig-zag chains infinity 1 [K(H2O)(2/2)](+) and form hydrogen bonds to neighboring selenium atoms.