THE EFFECT OF WATER-CONTENT ON THE PHYSICAL-PROPERTIES OF ALKALI-METAL METATUNGSTATE HYDRATES

Various alkali metal metatungstate hydrates, MI5 [H2W12O40].RH2O (M : Li+, Na+, K+) were synthesized by Freedman's method. The water content of products was varied by vacuum evaporation. The products were characterized with X-ray diffraction, IR spectroscopy and thermal analysis. The effect of water content on physical properties was investigated. Water vapor pressure was measured by the manometric static method, the proton transport number was determined from e. m. f. measurements and the a. c. impedance method was used for conductivity measurements. X-Ray diffraction and thermal analysis of MI6 [H2W12O40].RH2O with different R values showed there are different water sites in the crystal and that each sites has a specific dehydration temperature. Measurements of proton transport number indicated that the conduction was entirely protonic. The conductivities were 9.25×10-4 for Li6[H2W12O40]31.9 H2O and 1.84×l0-6 for K3 [H2W12O40].5.8 H2O S/cm. The conductivities increased with increasing water content. From these results, it was concluded that water molecules, interacting weakly with alkali metal ions and [H2W12O40]6- anions, are main contributors to conduction of MI6 [H2W12O40].RH2O. © 1990, The Chemical Society of Japan. All rights reserved.