Equilibria of aqueous solutions of isopolyniobotungstates-6 with c Nb : c W = 1 : 5

Abstract

Complex formation in the Nb6O198−-WO42−-H+-H2O system with cNb : cW = 1 : 5 and varied cNb + W0 = 10−2, 5 × 10−3, 2.5 × 10−3, and 10−3 mol/L) has been studied. Distribution diagrams were simulated for individual niobium(V) and tungsten(VI) isopolyanions and mixed isopolyniobotungstates for \(Z = \frac{{c_{H^ + }^0 }}{{c_{Nb + W}^0 }} = 0 - 3.0\) in an NaCl background electrolyte. We have shown that isopolyniobotungstates-6 of composition HxNbW5O19(3 − x)− are formed via HxNbnW6−nO19(2 + n − x)− (n=2, 3, 5) ions. The concentration formation constants and thermodynamic formation constants of isopolyniobotungstate anions (IPNTAs) in aqueous solution have been calculated. Salt Tl3NbW5O19·9H2O has been synthesized and identified by chemical analysis and IR spectroscopy.