Equilibrium in the acidified aqueous solutions of tungstate anion: synthesis of Co(II) isopolytungstates. Crystal structure of Co(II) paratungstate B Co_5[W_(12)O_(40)(OH)_2] ·37H_2O

摘要

The system of Na_2WO_4-HNO_3-KNO_3-H_2O was investigated by means of single-point pH- potentiometric titration, and subsequent mathematical modeling of the equilibrium processes revealed that hydroheptatungstate anion HW_7O_(24)~(5-)transforms into protonated forms of paratungstate B anion H_xW_(12)O_(40)(OH)_2~(10-).The mathematical modeling data were used to create a procedure for the synthesis of Co(II) sopolytungstates. Chemical and spectroscopic analyses of the products isolated from the systems of Na_2WO_4-HNO_3-Co(NO_3)_2-H_2O with different acidity allowed the determination of the conditions of Co(II) paratungstate B formation. The structure of the cobalt paratungstate B Co_5[W_(12)O_(40)(OH)_2]·37H_2O was confirmed by singlecrystal X-ray diffraction analysis.