Synthesis of Mn(II)-containing paratungstate B from aqueous solutions acidified by acetic acid

The method of pH-potentiometric titration and mathematical simulation were used to study the equilibrium processes in aqueous solutions of the WO42––CH3COOH–H2O system in the acidity range Z=(CH3COOH)/(Na2WO4)=0.8–1.7 at СW=0.01 mol L–1 and T=2980.1 K, a constant ionic strength being maintained by sodium nitrate as a background electrolyte ((NaNO3)=0.10 mol L–1). We developed the models of polyoxotungstate anions formation and the equilibrium transformation processes, which adequately describe experimental pH vs. Z dependences. It was found that acetic acid using to create the solution acidity that is necessary for the formation of isopoly tungstate anion contributes only to the formation of protonated paratungstate B anions Нх[W12O40(ОН)2](10–х)– (where x=0–4). We calculated the logarithms of the concentration equilibrium constants of the polyanion formation and plotted the distribution diagrams. Double sodium-manganese(II) paratungstate B Na8(H2O)28Mn(H2O)2[H2W12O42]4H2O was synthesized at Z=1.00 to confirm the results of the mathematical modeling. The chemical composition of the prepared salt was established by chemical elemental analysis, thermal analysis, FTIR spectroscopy, and single crystal X-ray analysis. The stepwise process of salt dehydration was studied by means of differential thermal analysis.