RAMAN SPECTRAL STUDY ON ISOPOLYTUNGSTATES IN AQUEOUS SOLUTION
(Department of Chemistry, Central South University of Technology,Changsha 410083, P. R. China)
Abstract: In the acidic aqueous Na2WO4solutions in a range ofZ(H+/WO2-4)=0~1.50, the chemical state of isopolytungstates has been studied using Raman spectroscopy. It was found that in the solution of Z≤1.25, the dominant polynuclear species at any time is paratungstate A, W7O6-24, which also exists at Z=1.42. During the aging of solution, paratungstate A is slowly transformed to paratungstate B, H2W12O10-42, which is easily deposited as the crystal Na10H2W12O42·27H2O, but the concentration of paratungstate B in the solution is too low to be detected. In the solution ofZ=1.42 and 1.50, there are probably metastable species, but metatungstate, H2W12O6-40, becomes the dominant species after long aging.
Key words: Raman spectra isopolytungstate paratungstate metatungstate