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

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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 K0.5V2O5 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-Ag0.68V2O5 type structure (R/Rw= 0.061/0.048), which involved a three-dimensional structure of the double-sheet V2O5 layer proposed in Part 1. K0.5V2O5 was converted into a hydrated phase, K0.3V2O5·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 K0.3V2O5·H2O to K0.5V2O5 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.