Hydro-flux synthesis and crystal structure of Tl3IO

Crystal structure of potassium orthoselenate(IV), K2SeO3

Crystal structure data for potassium orthoselenate(IV), K2SeO3, are reported for the first time. Colorless, block-shaped crystals were grown in a potassium hydro-flux, i.e. under ultra-alkaline conditions, within 10 h. K2SeO3 crystallizes isostructural with Na2SO3 and K2TeO3 in the trigonal space group P with lattice parameters a = 6.1063 (4) Å and c = 6.9242 (4) Å at 100 (1) K. In the trigonal-pyramidal, C 3v-symmetric [SeO3]2- anion, the bond length is 1.687 (1) Å, and the bond angle is 103.0 (1)°. Two of the three unique potassium cations exhibit a coordination number of six, and the third a coordination number of nine.

An unusual member of the solid solution series between cristobalite and potassium ferrate(III) obtained from hydroflux

Dark octahedral crystals of K1−x [Fe1−x Si x O2] with x ≈ 0.2 were synthesized under ultra-alkaline conditions in a KOH hydroflux at 200 °C. The compound is a member of the solid solution series between SiO2 and K[FeO2]. Due to its SiO2 content, K0.8[Fe0.8Si0.2O2] is much less sensitive to moisture than K[FeO2]. The crystal structure is a stuffed cristobalite with a charged framework of vertex-sharing [MO4/2] tetrahedra (M = Fe3+, Si4+) and potassium counter ions in the large voids of the framework. It has the pseudo-symmetry and metrics of the cubic space group F d 3 ‾ m $Fd\overline{3}m$ , but adopts the tetragonal space group I41 md with four formula units in the cell. Unlike other tectosilicates of this type, the [MO4/2]− tetrahedra are not regular but distorted to disphenoids. The O atom can be modeled by a huge disk-shaped ellipsoid or, better, by split atom positions forming a six-membered ring with a diameter of 1.1 Å. The M–O distances range from 1.66(2) to 1.96(2) Å, the M–O–M angles are 135(2)°, 137(1)°, and 151(1)°.

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.