Ph meter system

Potentiometric measurements were carried out using Molspin pH-meter system with Mettler Toledo InLab 422 semimicro combined electrode at 25 °C calibrated in hydrogen ion concentration using HCl (Irving et al. 1967 (link)). The ligands concentration was 8 × 10⁻⁴ mol/L and pH-metric titrations were performed in 0.1 mol/L KCl solution using sample volumes of 1.2 mL. Alkali (NaOH) was added by using a 0.25 ml micrometer syringe. The concentration of NaOH was 0.1 mol/L. Stability constants and stoichiometry of the complexes were calculated from titration curves using the SUPERQUAD program (Gans et al. 1985 (link)). The pH range where precipitation was observed was omitted during the calculations. Due to this fact some stability constants were only estimated, which is indicated in the “Results” section.

The potentiometric titration were performed on Molspin pH-meter system using a Mettler Toledo InLab®Micro combined electrode. The electrode was calibrated by titration hydrogen ion sample using HCl three times before each system. The KOH titrant (0.1 mol dm^− 3) was added from a 0.250 ml micrometer syringe and the concentration was calibrated by weight titrations of standard materials. All samples were titrated in thermostat vessel at 298 K over the pH range 2.5–11.5 under argon gas atmosphere. The ligand concentration was 8 × 10^− 4 mol dm^− 3 in solution the ionic strength was in 0.1 mol dm^− 3 KCl. The samples with metals ion system were prepared by added equimolar amounts of CuCl₂ and ZnCl₂ solutions where final ratio Cu(II):Zn(II):L = 1:1:1. The stability constants of the proton and metal complexes were calculated from titration curves by the HYPERQUAD 2008 (written by Peter Gans, Protonic Software) computer program (Gans et al. 1996 (link)). The standard deviations for each constants were computed and refer to random errors only. They were a good indication of the importance of a particular species in the equilibrium.

The potentiometry titrations were conducted on a MOLSPIN pH-meter system, using a Mettler Toledo InLab^®Micro combined electrode. The pH-meter system was calibrated by triple titration of hydrogen ion (HCl) before each measurement. The potentiometric experiments were performed in argon atmosphere over the pH range 3.0–11.5 at 298 K. The ligands were dissolved in HCl/KCl where pH = 3.0 and I = 0.1 M (KCl), the ligands concentration were 1 × 10⁻³ M. The accurate concentration of ligands solutions were determined by Gran method. The samples of each titration were prepared by adding equimolar amounts of CuCl₂ solutions. Titration volume were 1–1.5 ml and alkali (c(KOH) ~0.1 M) was added from a 0.250 ml micrometer syringe. The stability constants for the proton (β_i^(H)) and Cu(II) complexes (β_(CupHqLr)) were calculated by HYPERQUAD 2008 (written by Peter Gans, Protonic Software) and SUPERQUAD computer programs (Gans et al. 1985 (link), 1996 (link)). The protonation constants of ligands is determined by: β_i = [H_iL]/[H⁺]ⁱ[L] and the equilibrium of complex stability: β_pqr = [M_pH_qL_r]/[M]^p[H]^q[L]^r. Standard deviations were computed by these both programs and refer to random errors only.