Polytungstates of doubly-charged s- and d- metals’ cations

Abstract

The dissertation is dedicated to the investigation of equilibria in aqueous solutions of W(VI) in the presence of doubly-charged cations of s- and d-metals (barium, strontium, calcium, cadmium), determination of the thermodynamic characteristics of these equilibria, development of synthesis conditions, synthesis, and structural determination of calcium, strontium, barium, and cadmium paratungstates.
In Chapter 1, "Literature Review," the history of research on the state of tungsten(VI) anions in aqueous solutions is analyzed. Possible pathways for polycondensation processes leading to the formation of isopolytungstate anions and ionic associates with varying acidity, as well as the main methods for studying these processes, are discussed. The analysis covers known synthesis methods, structures, and properties of isopolytungstate compounds in general and specifically those involving doubly-charged s- and d-metal cations.
In Chapter 2, "Experimental Methodology," methods for standardizing the starting materials are presented. Physical methods for studying the state of tungsten(VI) anions in solution (pH-potentiometric titration, conductometric titration), followed by mathematical modeling of equilibria in solutions using the CLINP 2.1 program to determine concentration constants for ion pair formation are characterized. The methodology for determining thermodynamic constants for ion pair formation using the Pitzer method is described. Synthesis methods and qualitative and quantitative analyses of the composition of isolated salts of isopolytungstates of doubly-charged s- and d-metal cations are outlined, utilizing chemical elemental analysis and physical methods such as atomic absorption spectroscopy, IR and Raman spectroscopy, scanning electron spectroscopy, energy-dispersive X-ray spectroscopy, and X-ray structural analysis.
In Chapter 3, "Study of Interactions in Aqueous Solutions of the M²⁺ – WO₄²⁻ – H⁺ – H₂O Systems," pH-potentiometric studies of W(VI) polycondensation processes with the simultaneous formation of ion associates with M^(2+) in solutions of the {M^(2+)–[WO_4^(2-)–H^+ (Z=1,00)]}–H^+–H_2 O (M^(2+)=〖Ba〗^(2+);〖Cd〗^(2+)) or {M^(2+)–[WO_4^(2-)–H^+ (Z=0,60)]}–H^+–H_2 O (M^(2+)=〖Ca〗^(2+);〖Sr〗^(2+)) systems were carried out at T=298 K with a concentration of C(WO_4^(2-) )=〖10〗^(-2) mol∙L^(-1) and a molar ratio of C(M^(2+) ):C(WO_4^(2-) )=1:12 in the ionic strength range of I=0,05÷0,40 mol∙L^(-1).
In Chapter 4, "Synthesis and Characterization of Barium, Cadmium, Calcium, and Strontium Compounds with Isopolytungstate Anions," based on the study of the reaction conditions for polycondensation and ion association formation, new methods for synthesizing barium, cadmium, strontium, and calcium paratungstates have been developed. These methods use solution acidity instead of pH and a non-stoichiometric ratio of C(M^(2+) ):C(WO_4^(2-) )=1:12. The synthesis of compounds with the paratungstate B anion in a wide range of acidity has confirmed the stabilization of this anion through the formation of ion associations.