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1 Polish Journal of Chemistry

1 2006

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Investigation of Heteropoly Niobotungstolanthanidate Ions Equilibria in the Aqueous Solutions at Different Ionic Strengths

Rozantsev G., Radio S., Kozlova T.

Polish Journal of Chemistry

2006

Vol. 80, nr 2

235-245

The condensation process in the system: Ln3+-H3Nb6O19 5 -WO4 2 -OH-(H+)-H2O (Ln = Ho, Nd; ni(Nb):ni(W) = 9:1) has been investigated. According to the results of potentiometric titrations, the model of the condensation process has been proposed. Diagrams of mixed heteropoly niobotungstolanthanidate anions (HPNTLA) distribution within an intervals ZH+ = [ni(H+ )]/[ni(W) + ni(Nb)] = 0.00÷0.30 and ZOH- = [_(OH-)]/[ni(W) + ni(Nb)] = 0.00÷0.36 have been drawn. It has been shown that at Z H+ > 0.30 there occurs a destruction of heteropolyanions (HPA). Concentration and thermodynamic constants of HPA formation have been determined. Existence of HPNTLA has been confirmed by chemical and IR-spectroscopic analyses of Tl6H4[HoNb9W(OH)8O28]ni4.0H2O, which was isolated from a solution with Z H+ = 0.08. It has also been shown, that HPNTLAkeeps the ratio of Nb:W = 9:1 within the entire interval ZOH-. The main destruction phases of Tl6H4[HoNb9W(OH)8O28]x4.0H2O have been determined by X-ray powder diffraction analysis.