Study of the Complex Formation Process in the Iron (III)-1-Phenyl-2,3-Dimethylpyrazolin-5-Thion-6 mol/l HCl + Acetone System by the Potentiometric Method

The complex formation of iron (III) ions in a wide range of temperatures in a mixed solvent was studied by the potentiometric method using a redox electrode based on 1-phenyl-2,3-dimethylpyrazoline-5-thione and its oxidized form. The study shows that titration of the iron (III)--1-phenyl-2,3-dimethylpyrazoline-5-thione--6 mol/l HCl (HCl + acetone, ratio 1:3) system at a temperature of 273--318 K results in a regular increase in the potential indicator electrode. It was found that in the system under consideration four complex forms of compositions are formed: [FeL(H2O)5]3+, [FeL2(H2O)4]3+, [FeL3(H2O)3]3+ and [FeL4(H2O)2]3+. For each complex particle, their stability constants are determined by the Bjerrum method. Summarizing the experimental and theoretical data, it was established that the iron (III) complexes obtained in the 6 mol/l HCl medium are more stable than the complexes obtained in a mixed solvent with 1-phenyl-2,3-dimethylpyrazoline-5-thione. The values ΔH and ΔG of reactions of the formation of 1-phenyl-2,3-dimethylpyrazoline-5-thione complexes were found by Clark --- Glu method using the regression method. The corresponding patterns in the change in values ΔH, ΔG and ΔS of formation of complexes were revealed. To determine the region of dominance and the maximum yield of a particular complex particle, depending on the concentration of the organic ligand in the solution, distribution diagrams were constructed, according to which the maximum yield of a complex particle and the region of its dominance can be found at any point The work was carried out in accordance with the research plan of the laboratory "Synthesis and testing of coordination compounds" named after Corresponding Member of Tajik Academy of Sciences, Dr. Sc. (Chem.), Professor A.A. Aminjanov, Research Institute of the Tajik National University (project no. 0119TJ01007)