Search

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.

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 composition and stability of coordination compounds of the anions of maleic (H2L) and succinic (H2Y) acids with copper(II) ions in water-ethanol solutions is studied by means of potentiometric titration at a sodium perchlorate ionic strength of 0.1 and a temperature of 298.15 K. The composition of the water-ethanol solvent was varied from 0 to 0.7 molar parts of ethanol for maleic acid and from 0 to 0.4 molar parts for succinic acid. The stability of monoligand complexes of copper ions with the anions of maleic and succinic acids grows with increase of ethanol concentration from 3.86 to 6.62 for logβCuL and from 2.98 to 6.01 for logβCuY. It is shown that a monotonic rise in stability upon an increase in the content of ethanol in solution is observed, while the values of logβCuL change more sharply. The succinic acid anion forms a stronger complex with copper ions than maleic acid anions do at an ethanol content of 0.4 molar parts. The possibility of the formation of a protonated CuHY+ particle is established.

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.