ANALYSIS OF THE STATE OF ISOPOLYNIOBOTUNGSTATE ANIONS (Nb:W = 3:3) AND THEIR SYNTHESIS FROM AQUEOUS SOLUTIONS

Abstract

The formation of complexes in the system Nb6O19 8––WO4 2––H+–H2O, where Nb:W = 3:3 and cNb+W 0 = 10, 5, 2.5 and 1 mmol/L, was studied by pH–complexonometric titration. Using computer modeling of the processes of complexes formation (CLINP 2.1 software), concentrational constants of the mixed isopolyniobotungstate anions formation were obtained, (background electrolyte is NaCl) and their distribution diagrams were built. The thermodynamic constants of HxNb3W3O19 (5–x)– (􀉯 = 0–3) formation were calculated, and it was shown that the formation of these anions takes place only after the polycondensation of the initial orthotungstate anions. Calcium and Thallium salts (Ca1.5􀉇2Nb3W3O19·12H2O and Tl5–x􀉇xNb3W3O19·nH2O, respectively, x = 1–3) were prepared and characterized by X–ray spectral analysis, scanning electron microscopy, and IR-spectroscopy.

Keywords

• polyoxometalates
• isopolyanion
• isopolyniobotungstate
• Lindqvist anion
• modeling complex formation in solution.