Layered structures of hydrated vanadium oxides. Part 4.—Single-crystal structure and phase conversion of the unhydrated potassium intercalate K0.5V2O5

Abstract

An unhydrated phase of the potassium intercalate of the hydrated vanadium oxides in Part 1 has been synthesized in a hydrothermal VO(OH)₂–KCl system. It is formulated as K_0.5V₂O₅ and adopts the monoclinic system C2/m with a= 11.688(2)Å, b= 3.668(1)Å, c= 9.505(2)Å and β= 92.24(1)°. A single-crystal structure analysis revealed a δ-Ag_0.68V₂O₅ type structure (R/R_w= 0.061/0.048), which involved a three-dimensional structure of the double-sheet V₂O₅ layer proposed in Part 1. K_0.5V₂O₅ was converted into a hydrated phase, K_0.3V₂O₅·H₂O, by oxidation or by lowering the potassium content, which expanded the layer spacing from 9.50 Å to 10.88 Å. The reverse change from K_0.3V₂O₅·H₂O to K_0.5V₂O₅ was effected by using a reducing agent such as a potassium iodide solution. The hydration process seems to be controlled by the interlayer potassium content.