Structural Effects and Microheterogeneity in Concentrated Solutions and Their Role in the Formation of Cadmium Chloride Complexes

Abstract

The proton relaxation rate and Raman spectra in the regions of vibrations of the Cd-Cl, Cd-OH₂ groups and bending vibrations eta₄ of nitrate ions in the systems CdAn₂-NaCl-H₂O (An = Cl^-, ClO₄ ^-, NO₃ ^-) were measured. In the range of subeutectic concentrations of cadmium salts all possible forms of chloride complexes of cadmium are formed. In the posteutectic region the formation of complexes is structurally induced; it depends on the nature of dominating cybotactic groups and is limited to the formation of only low-coordinate forms. The mechanisms of the formation of chloride complexes in perchlorate and nitrate systems were proposed. It was concluded that, in contrast to the chloride system, the nitrate and perchlorate systems in the presence of sodium chloride are characterized by structural microheterogeneity. The distinctions in the nature of the microheterogeneity and its effect on the complex formation were considered. The solubility polytherm and Raman spectra of the system Cd(NO₃)₂-NaCl-H₂O with a high content of the both salts were measured. The causes of abnormally high mutual solubility of nitrate salts in multicomponent solutions containing salts that crystallize in the hydrated and anhydrous forms were suggested.