Composition and stability constants of copper(II) complexes with succinic acid determined by capillary electrophoresis

The advantage of capillary electrophoresis was demonstrated for studying a complicated system owing to the dependence of direction and velocity of the electrophoretic movement on the charge of complex species. The stability constants of copper(II) complexes with ions of succinic acid were determined by capillary electrophoresis, including the 1 : 2 metal to ligand complexes which are rarely mentioned. The measurements were carried out at 25 °C and ionic strength of 0.1, obtained by mixing the solutions of succinic acid and lithium hydroxide up to pH 4.2–6.2. It was shown that while pH was more than 4.5 the zone of copper(II) complexes with succinate moves as an anion. It is impossible to treat this fact using only the complexes with a metal-ligand ratio of 1 : 1 (CuL0, CuHL+). The following values of stability constants were obtained: log β(CuL) = 2.89 ± 0.02, log β(CuHL+) = 5.4 ± 0.5, log β(CuL22−) = 3.88 ± 0.05, log β(CuHL2−) = 7.2 ± 0.3.