Isopolyniobotungstate HxNb2W4O19 (4–x)– Ions: Analysis of the State of the Ions in Aqueous Solutions, Formation Constants Calculation and Thallium Salts Synthesis

By means of pH-potentiometric titration, the processes of the complexes formation in the system Nb6O19 8––WO4 2––H+–H2O with CNb : CW = 2 : 4 was studied at different Nb + W concentrations. Exerimental data, being processed by mathematical modeling, allowed to obtain the distribution diagrams of individual niobium and tungsten isopoly anions, and mixed isopolyniobotungstates in the range of Z = C0 H+/C0 Nb+W = 0 – 2.0 (background electrolyte is NaCl). Concentrational and thermodynamic formation constants were calculated using quasi–Neuton method (CLINP 2.1 software) and it was shown, that the formation of isopolyniobotungstates (HxNb2W4O19 (4–x)–, x = 0 – 2) of the 6th row of Periodic table proceeds through intermediate Nb3W3O19 5– ion formation. Thallium salts Tl3HNb2W4O19 • 10H2O and Tl2H2Nb2W4O19 • 10H2O were isolated and characterized by elemental and EDX spectral analysis, electron microscopy and FTIR-spectroscopy.