Stability of copper(II) complexes with nicotinate ion in water solutions of ethanol and dimethyl sulfoxide

The stability constants of copper(II) complexes with nicotinate ion in water–ethanol and water–dimethyl sulfoxide mixtures are determined potentiometrically at 25.0 ± 0.1°C at ionic strength of 0.25 (NaClO4). The stability of the copper(II) nicotinate complex significantly increases with ethanol content in the solution, thus making it possible to control the biologically important process by varying the solvent composition. The increase in DMSO concentration causes a less noticeable rise in stability, with its maximum observed at 0.1 dimethyl sulfoxide mole fractions. A comparative analysis of the findings and stability constants of Cu²⁺ complexes with pyridine-type ligands is carried out. The results are discussed using the solvation thermodynamics approach.