Chalcogenides by Reduction of their Dioxides in Ultra-Alkaline Media.

The reaction of chalcogen dioxides ChO2 (Ch=Se, Te) with As2 O3 in a 30 molar KOH hydroflux at about 200 °C yielded crystals of potassium trichalcogenides K2 Ch3 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 K2 TeSe2 crystallizes isostructural to K2 S3 and K2 Se3 . 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 As2 O3 , colorless monochalcogenide Ch2- or orange Se2 2- and purple Te2 2- anions are dominating the solutions.