Complex formation of molybdenum (V) with 1-phenyl-2,3-dimethylpyrazoline-5-thion in 4 mol/L HCI medium at 273-338 K

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The process of complexation of molybdenum (V) with 1-phenyl-2,3-dimethylpyrazolin-5-thione in a 4 mol/l HCI medium in the temperature range 273-338 K was studied by the potentiometric method. It has been shown that the reduced form of the 1-phenyl-2,3-dimethylpyrazolin-5-thione molecule is involved in the complex formation reaction. Using the data of potentiometric studies, the change in the energy value (ΔE) of the (NH4)2[MoOCI5]2-1-phenyl-2,3-dimethylpyrazolin-5-thione-4 mol/l HCl system, the equilibrium concentrations of 1-phenyl-2,3-dimethylpyrazolin-5-thione, formation function values, step and general stability constants of oxochloro-1-phenyl-2,3-dimethylpyrazolin-5-thione complexes of molybdenum (V) formed in HCl solutions in the temperature range 273-338 K. The stability constants of oxochloro-1-phenyl-2,3-dimethylpyrazolin-5-thione complexes of molybdenum (V) were refined using the Bjerrum graphical method. The temperature coefficient method was used to estimate the thermodynamic functions of complex formation processes in the (NH4)2[MoOCI5]-1-phenyl-2,3-dimethylpyrazolin-5-thione - 4 mol/L HCI system. The domains of dominance and the maximum yield of each complex form are found. It has been established that in the studied system (NH4)2[MoOCI5]-1-phenyl-2,3-dimethylpyrazolin-5-thione - 4 mol/l HCI during the interaction of the MoO3+ ion with 1-phenyl-2,3-dimethylpyrazolin- 5-thione in the entire temperature range of the experiment forms 5 mononuclear coordination compounds containing from one to five coordinated molecules of the organic ligand. It was found that with increasing temperature, the values of the general stability constants of coordination compounds decrease, which confirms the exothermicity of the reaction of formation of oxochloro-1-phenyl-2,3-dimethylpyrazoline-5-thione compounds of molybdenum (V). The experimentally found values of enthalpy made it possible to assume that the reaction of complex formation between the MoO3+ ion and the molecules of nitrogen- and sulfur-containing heterocyclic 1-phenyl-2,3-dimethylpyrazolin-5-thione proceeded exothermically spontaneously. Based on the above equations, all calculations were carried out using a computer in the Excel programming language, Borland Delphi, Windows 7 operating system.