LAYERED STRUCTURES OF HYDRATED VANADIUM-OXIDES .4. SINGLE-CRYSTAL STRUCTURE AND PHASE CONVERSION OF THE UNHYDRATED POTASSIUM INTERCALATE K0.5V2O5

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) Angstrom, b = 3.668(1) Angstrom, c = 9.505(2) Angstrom and beta = 92.24(1)degrees. A single-crystal structure analysis revealed a delta-Ag0.68V2O5 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. 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 Angstrom to 10.88 Angstrom. 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.