The reaction of chalcogen dioxides ChO(2) (Ch=Se, Te) with As2O3 in a 30 molar KOH hydroflux at about 200 degrees C yielded crystals of potassium trichalcogenides K(2)Ch(3) with dimensions up to 2 cm. Arsenic trioxide acts as electron donor and is oxidized to arsenate(V). The new heterochalcogenide anion (TeSe2)(2-) formed when starting from SeO2 and TeO2 simultaneously. The compound K2TeSe2 crystallizes isostructural to K2S3 and K2Se3. The unexpected redox reaction as well as the precipitation of hygroscopic compounds from an aqueous solution are attributed to a strongly reduced activity of water. The reactions were studied by Raman and UV/Vis spectroscopy. Depending on the concentration of As2O3, colorless monochalcogenide Ch(2-) or orange Se-2(2-) and purple Te-2(2-) anions are dominating the solutions.
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