Strontium Isopoly Tung states: Synthesis and Properties

By single-point pH-metric titration method we investigated the interactions in the system of Na2WO4 - HNO3 - KNO3 - H2O in the conditions that are close to equilibrium. We also showed by mathematical modeling of the processes (Newton's method, CLINP 2.1 software) that interconvertion between particular isopoly tungstate anions (ITA) takes place and this leads to the decrease in concentration of hexatungstate W6O20(OH)2 6- and hydroheptatungstate HW7O24 5- anions with simultaneous increase of quantity of paratungstate B HxW12O40(OH)2 (10-x) - and metatungstate W12O38(OH)2 6- anions in the system. The results of the modeling were proven by the successful synthesis of strontium salts with ITA. From non-equilibrium solution with different acidity Z = n(H+) / n(WO42-) we isolated strontium paratungstate B Sr5[W12O40(OH)2]ź27H2O (Z = 1.14-1.17) and strontium hydroheptatungstate Sr5[HW7O24]2ź30H2O (Z = 1.29). From the equilibrium solution the only strontium paratungstate B Sr5[W12O40(OH)2]ź27H2O (Z = 1.17-1.33) precipitates. All the salts synthesized were characterized by elemental analysis, FTIR spectroscopy, X-ray diffraction, and DTA.