Equilibrium in the acidified aqueous solutions of tungstate anion: synthesis of Co(II) isopolytungstates. Crystal structure of Co(II) paratungstate B Co5[W12O40(OH)2] · 37H2O.

The system of Na2WO4-HNO3-KNO3-H2O was investigated by means of single-point pH-potentiometric titration, and subsequent mathematical modeling of the equilibrium processes revealed that hydroheptatungstate anion HW7 [image omitted] transforms into protonated forms of paratungstate B anion HxW12O40 [image omitted]. The mathematical modeling data were used to create a procedure for the synthesis of Co(II) isopolytungstates. Chemical and spectroscopic analyses of the products isolated from the systems of Na2WO4-HNO3-Co(NO3)2-H2O with different acidity allowed the determination of the conditions of Co(II) paratungstate B formation. The structure of the cobalt paratungstate B Co5[W12O40(OH)2] · 37H2O was confirmed by single-crystal X-ray diffraction analysis. [ABSTRACT FROM AUTHOR]