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, K2WO4, decomposes at high pressures to give K2W2O7 and other products. Single crystals of K2W2O7 could be synthesized from a mixture of K2WO4 + WO3 at 40kbar, 1000 °C. The crystals are monoclinic, space group P21/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 WO6-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. Rb2W2O7, synthesized from a Rb2WO4/WO3-mixture at 40 kbar, 1000 °C, is isostructural with K2W2O7 (a = 3.9645(4) Å, b = 14.119(1) Å, c = 6.0415(5) Å,β = 90.446(9)°.