STABILITY OF COMPLEXES OF Ni(II) AND 18-CROWN-6 ETHER IN WATER-ETHANOL SOLVENTS

The stability constants of the nickel(II) complex with 18-crown-6 in aqueous and aqueous ethanol solutions with a content of 0.20 and 0.30 mole fractions of ethanol at 298.15 K. were determined by spectrophotometry. Electronic absorption spectra were recorded in the wavelength range of 250-900 nm and optical densities of 0-4 rel. units. 2 ml of nickel (II) nitrate solution with an initial concentration of 0.13-0.15 mol/l was placed in a standard quartz cuvette (10 mm). A solution of 18-crown-6 with an initial concentration of 0.30-0.40 mol/l was used as a titrant. In the cell the 25 titrant injections of 50 µl were added. Water or a water-ethanol solvent was used as a reference solution. The extinction coefficients of nickel(II) ions were preliminarily determined for wavelengths in the range from 250 to 900 nm in the corresponding solvent, which were used in further calculations. With increasing ethanol concentration, a tendency towards a decrease in the stability of the [Ni18K6]2+ complex particle is observed. The solvation contributions of reagents to the Gibbs energy in the [Ni 18C6]2+formation reaction in aqueous ethanol solutions have been analyzed. The obtained results were analyzed from the standpoint of the solvation approach. Changes in the Gibbs energy of 18C6 solvation at transfer from water to aqueous ethanol solvents are insignificant. Changes in the solvate state of [Ni 18C6]2+ are determined by a change in the solvation of Ni2+(ΔtrG°([Ni 18C6]2+)≈ΔtrG°(Ni2+)) and demonstrate a slight weakening of solvation during the transition from water to X(EtOH) = 0.10 mole fraction. A further increase in the ethanol content in the solvent leads to an increase in the solvation of Ni2+. As a result, changes in the Gibbs transfer energy of the reaction have almost zero values. The results obtained were compared with the thermodynamics of the complexation of silver (I) ion with 18C6 in a water-ethanol solvent. For citation: Usacheva T.R., Kuranova N.N., Kabirzoda D.N., Kryukova O.V. Stability of complexes of Ni(II) and 18-crown-6 ether in water-ethanol solvents. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 10. P. 105-113. DOI: 10.6060/ivkkt.20246710.7061.