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The effect aqueous ethanol solvents have on the stability of coordination compounds between Cu(II) ions and anions of succinic (Y2–) and maleic (L2–) acids is studied via UV–Vis spectrophotometry. Logarithms of stability constants for succinate and maleate complexes are compared to ones obtained via potentiometric titration. Quantum chemistry calculations are performed for the structures of maleic and succinic acids and complexes of them with Cu(II) ions to explain the difference between the stabilities of succinate and maleate complexes.

The paper provides an overview of own data on complexation of nickel (II), cobalt (II) and cooper (II) ions with succinic acid anion in water-organic mixed solvents. Proper data are compared with data reported in literature for d-metal complexes with anions of maleic and succinic acids. The effect of aqueous ethanol solvent compositions on the stability of coordination compounds of M2+ with succinic acid anion as well as on рК values of stepwise succinic acid dissociation was carried out by a potentiometric titration at ionic strength of 0.1 maintained with sodium perchlorate at 298.15 ± 0.10 K. Mono ligand complexes of Ni2+, Co2+ and Cu2+ ions with succinic acid anion become stronger when ethanol content rises. In aqueous solutions Cu2+ ion forms stronger complexes with succinic and maleic acid anions than Ni2+ and Co2+ ions. In the studied water - ethanol solution this ratio is maintained for complexes with succinic acid anion, but a water-isopropanol solvent exerts leveling effect on the stability of complexes of nickel (II) and cobalt (II). An increase in the stability of complexes of d-metal with anions of maleic and succinic acids is due to the destabilization of the ligand with increasing ethanol concentration. The principal contribution of the changes in the solvation state of ligand is a typical for the stability changes of d-metal complexes with amine, glycinate, and acetate type ligands in water-organic mixed solvents. For citation: Tukumova N.V., Usacheva T.R., Thuan Tran Thi Dieu, Sharnin V.A., Giancola C. Stability of coordination compounds of some d-metal ions with succinic acid anion in aqueous-ethanol solvents. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N 9-10. P. 15-22

Stability constants of the coordination compounds of nickel(II) and cobalt(II) ions with succinic acid anion in water–ethanol solvents are determined via potentiometric titration at ionic strength of 0.1 and at T = 298.15 K. It is found that logβ values of monoligand complexes of these ions and succinic acid anions rise along with the content of ethanol in solution (XEtOH = 0–0.7 mole fractions). Based on an analysis of the thermodynamic characteristics of the solvation of the reagents involved in complex formation, it is found that the increased stability of succinate complexes of nickel(II) and cobalt(II) ions in water–ethanol solvents is mainly determined by the weakening of the solvation of succinic acid anion (Y2−).

The Gibbs energies of transferring succinic acid from water to aqueous ethanol and aqueous dimethylsulfoxide solvents are determined according to solubility. An increase in the negative values of the Gibbs energy upon moving from water to aqueous–organic solvents is observed. The effect the composition of solvents has on the acid–base properties of succinic acid is analyzed using the thermodynamic solvation approach. It is shown that the main contribution to the shift of the acid–base equilibria of succinic acid in aqueous ethanol and aqueous dimethylsulfoxide comes from the weakening of the solvation of its deprotonated forms.

Composition and stability of coordination compounds of nickel(II) and cobalt(II) ions with maleic acid anion in aqueous isopropanol solutions (H2O-IPA) of composition χIPA = 0–0.5 mole fraction was studied by potentiometric titration at ionic strength of 0.1 maintained with sodium perchlorate at 298.15 K. Monoligand complexes of Ni2+ and Co2+ ions with maleic acid anion become stronger when isopropanol content rises. In the solvent of the studied composition, Co2+ ions form less stable complexes than Ni2+ ions that corresponds to the Irving-Williams series established for aqueous solutions. Variations in complex stability are more expressed at small IPA content and differ within experimental error at χIPA = 0.5 mole fraction. Obtained results were compared with literature data for akin compounds.