Hochdrucksynthese und Kristallstruktur von Kalium- und Rubidiumdiwolframat(VI), K₂W₂O₇ und Rb₂W₂O₇ / High-Pressure Synthesis and Crystal Structure of Potassium and Rubidium Ditungstate(VI), K₂W₂O₇ und Rb₂W₂O₇

Abstract

Potassium tungstate, K 2 WO 4 , decomposes at high pressures to give K 2 W 2 O 7 and other products. Single crystals of K 2 W 2 O 7 could be synthesized from a mixture of K 2 WO 4 + WO 3 at 40kbar, 1000 °C. The crystals are monoclinic, space group P2 1 /c, with a = 3.883(1) A, b = 13.653(4) Å, c = 5.960(1) Å, β = 90.40(3)°, and Ζ = 2. The structure is comprise of distorted WO 6 -octahedra (W–O = 1.75-2.13 A) which are connected by corner- and edgesharing, thus forming layers with a sequence ABAB ... along [010]. The potassium ions are situated between the layers with K–O distances of 2.66-3.04 A. Rb 2 W 2 O 7 , synthesized from a Rb 2 WO 4 /WO 3 -mixture at 40 kbar, 1000 °C, is isostructural with K 2 W 2 O 7 (a = 3.9645(4) Å, b = 14.119(1) Å, c = 6.0415(5) Å,β = 90.446(9)°.