Isopoly Tungstate Anions in Water–Dimethyl Sulfoxide Solutions

Abstract

The formation of isopoly tungstate anions (IPTAs) in water–dimethyl sulfoxide (DMSO) solutions was studied by potentiometric titration, followed by mathematical modeling, and electronic absorption spectroscopy. Logarithmic equilibrium constants and Gibbs free energies were calculated for IPTA formation from $$\rm{WO}_4^{2-}$$ and Н+ in the $$\rm{WO}_4^{2-}$$ –H+(DMSO = dimethyl sulfoxide) system for various solution acidities Z=v(H+)/v( $$\rm{WO}_4^{2-}$$ ). A scheme was suggested for IPTA interconversions at various DMSO contents in solution. Dimethyl sulfoxide was found to have a stabilizing effect on [W7O24]6– and [W10O32]4– anions. The distribution diagrams and the calculated thermodynamic parameters of IPTA formation were used to determine optimal conditions for preparing decatungstates from water–DMSO solutions, which consisted in using sodium tungstate solutions acidified to Z = 1.60 and containing ϕ(DMSO) = 40%.