Chalcogenides by Reduction of their Dioxides in Ultra‐Alkaline Media

Abstract

The reaction of chalcogen dioxides ChO2 (Ch=Se, Te) with As2O3 in a 30 molar KOH hydroflux at about 200 °C yielded crystals of potassium trichalcogenides K2Ch3 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 Ch2− or orange Se22− and purple Te22− anions are dominating the solutions.

Formation of Tetraselenodiarsenate(II) Anions in Ultra‐alkaline Medium

“…At a reactant concentration of 0.6 mol/L, a weak band was found at 253 cm À 1 that increased in intensity with growing amount of starting materials. This symmetrical band is different from the known SeÀ Se vibrations of polyselenide anions observed in hydroflux solutions [13] and occurs in the energy range typical for AsÀ Se bond vibrations. [22] Beside this reduced selenium-and arsenic-containing species, monoselenide and arsenate(V) anions are present in the solution that may be involved in the formation of (As 2 Se 4 ) 4À anions.…”

“…At the lower q (Se) of 1.2, the triselenide K 2 Se 3 forms [13] . In previous experiments with q (Se)=2, colorless solutions containing monoselenide anions were obtained with reactant concentration of 0.25 mol/L with respect to selenium (Equation 1) [13] . In the synthesis of K 4 (As 2 Se 4 ) ⋅ 2H 2 O, a threefold higher reactant concentration was used, resulting in a yellow solution.…”

“…Under hydroflux conditions, As 2 O 3 dissolves as arsenate(III), which is able to reduce selenate(IV) to selenide ions (Equation 1). [13] 3…”

“…[13] In previous experiments with q(Se) = 2, colorless solutions containing monoselenide anions were obtained with reactant concentration of 0.25 mol/L with respect to selenium (Equation 1). [13] In the synthesis of K 4 (As 2 Se 4 ) • 2H 2 O, a threefold higher reactant concentration was used, resulting in a yellow solution. To characterize the species causing the color change, experiments were performed with different reactant concentrations and analyzed by Raman spectroscopy (Figure S3).…”

Chalkogenide durch Reduktion ihrer Dioxide in ultra‐alkalischen Medien

“…Gleichung (4) fasst die Reduktion der Dichalkogenid-Anionen zusammen: [27,28] Rçntgenbeugungsexperimente an schwarzen Einkristallen von K 2 Se 3 (Cmc2 1 )u nd K 2 Te 3 (Pnma)b estätigten die bekannten Strukturen. [4,5] [58] Angewandte Chemie Forschungsartikel 22746 www.angewandte.de Se-Te-Se Winkel von 97.6(1)8 8.D as (TeSe 2 ) 2À -Anion wurde bereits (2,2,2-crypt-K) 2 (TeSe 2 )•en (en = Ethylendiamin) [29] und [Mn(en) 3 ](TeSe 2 ) [30] beobachtet und weist darin Te -Se-Bindungslängen von etwa 250 pm und 250.3(1) pm sowie Se-Te -Se Winkel von 111.3(1)8 8 bzw.1 02.6(1)8 8 auf.I nd iesen Strukturen sind die (TeSe 2 ) 2À -Anionen weit voneinander getrennt und interagieren darüber hinaus mit den Wasserstoffatomen der organischen Liganden. Die grçßeren Se-Te-Se Winkel stehen im Einklang mit den kürzeren Te -Se Bindungslängen, die die Abstoßung zwischen den terminalen Atomen erhçhen.…”