Effect of Ionic Strength on the Stability and Thermodynamic Properties of Rhenium(v) Complexes With N-Ethylthiourea

The complex formation process in the system ReOCl – O/Red – HCl (O – bis – N – ethyl formamide disulfide (HDEFds), Red – N – ethylthiourea (Etu)) was studied by potentiometric titration in the temperature range 273.1–338.1 K, and the lgK values of the complexes were determined. Using the lgK values, the thermodynamic parameters of the process () were calculated. It was found that during the complexation of rhenium(V) with N-ethylthiourea, the exothermicity of the process decreases with increasing number of coordinated ligand molecules. It was revealed that the most favorable condition for the formation of stable complexes is a concentration of 4 mol/L HCl; i.e., when the hydrochloric acid concentration decreases from 6 to 4 mol/L, the stability of the resulting complexes increases.