All rights reserved https://phaidrabg.bg.ac.rs/o:28848 doi:10.3184/146867818X15319903829164 ISSN: 1468-6783 info:eu-repo/semantics/article Impact of chloride concentration on ligand substitution reactions of zinc(II) complexes with biologically relevant nitrogen nucleophiles 2018 Keywords: zinc(II) complexes, nitrogen nucleophiles, chloride substitution eng Abstract: The mole-ratio method was used to determine the metal–ligand stoichiometry between [ZnCl2(en)] and [ZnCl2(terpy)] (where en = 1,2- diaminoethane or ethylenediamine and terpy = 2,2′:6′,2′′-terpyridine) and imidazole at pH 7.2 in the presence of different chloride concentrations. The results indicated step-wise formation of 1:1 and 1:2 complexes in the presence of 0.010 M NaCl and 1:1 complexes in the presence of 0.001 M NaCl for the [ZnCl2(en)] complex. These results are correlated with additional coordination of chlorides in the first coordination sphere and with changes in coordination geometry. In the presence of 0.001 M NaCl the five-coordinate complex anion [ZnCl3(en)]– is formed initially and then a substitution reaction with imidazole occurs. In the presence of 0.010 M NaCl the octahedral complex anion [ZnCl4(en)]2– is formed. Additional coordination of chloride in the [ZnCl2(terpy)] complex is not found and the metal–ligand stoichiometry is 1:2. The kinetics of ligand substitution reactions of zinc(II) complexes and biologically relevant nitrogen nucleophiles such as imidazole, 1,2,3-triazole and L-histidine were investigated at pH 7.2 as a function of nucleophile concentration in the presence of 0.001 M and 0.010 M NaCl. The reactions were followed under pseudo first-order conditions by UV-Vis spectrophotometry. The substitution reactions included two steps of consecutive displacement of chlorido ligands with changes only in the coordination geometry of the [ZnCl2(en)] complex. The order of reactivity of the investigated nucleophiles for the first reaction step towards both complexes was L-histidine > 1,2,3-triazole > imidazole, while in the presence of 0.010 M NaCl the most reactive ligand was 1,2,3-triazole towards the [ZnCl2(en)] complex. Progress in Reaction Kinetics and Mechanism 43(3-4) Soldatović, Tanja Selimović, Enisa application/pdf 642291 bytes