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.

中文翻译：

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氯化物浓度对锌 (II) 配合物与生物相关氮亲核试剂的配体取代反应的影响

摩尔比方法用于确定 [ZnCl2(en)] 和 [ZnCl2(terpy)] 之间的金属配体化学计量比（其中 en = 1,2-二氨基乙烷或乙二胺，terpy = 2,2':6'， 2″-三联吡啶)和咪唑在不同氯化物浓度的存在下，pH 7.2。结果表明 [ZnCl2(en)] 复合物在 0.010 M NaCl 存在下逐步形成 1:1 和 1:2 复合物，在 0.001 M NaCl 存在下形成 1:1 复合物。这些结果与第一配位球中氯化物的额外配位以及配位几何形状的变化相关。在 0.001 M NaCl 存在下，首先形成五配位复合阴离子 [ZnCl3(en)]-，然后发生与咪唑的取代反应。在 0.010 M NaCl 存在下，形成八面体复合阴离子 [ZnCl4(en)]2-。未发现 [ZnCl2(terpy)] 复合物中氯化物的额外配位，金属-配体化学计量比为 1:2。在 pH 7.2 下研究了锌 (II) 配合物和生物相关的氮亲核试剂（如咪唑、1,2,3-三唑和 L-组氨酸）的配体取代反应动力学，作为亲核试剂浓度的函数，在 0.001 M 和0.010 M 氯化钠。通过紫外-可见分光光度法在伪一级条件下跟踪反应。取代反应包括氯配体连续置换的两个步骤，仅在 [ZnCl2(en)] 配合物的配位几何结构中发生变化。所研究的亲核试剂对两种复合物的第一步反应的反应性顺序是 L-组氨酸 > 1,2,3-三唑 > 咪唑，而在 0.