配合物生成反应速率常数与平衡常数之间的直线自由能关系 II: 镍(II)-N-(对位取代苯基)氨基乙酸配合物的生成反应动力学研究

应用断流分光光度计(Stopped-Flow Spectrophotometer)研究了镍(II)与N-(对位取代苯基)氨基乙酸-(ρ-RC6H4NHCH2COOH, R=CH3O, CH3, H, Cl, 简写为NROH或HL)在25℃及30%(v/v)乙醇溶液中生成配合物的反应动力学. 实验结果表明, 不仅氨基酸配体的负离子(NRO^-或L^-)具有较高的反应活性, 而且两性离子(HN^+RO^-或^+HL^-)也是有效的反应配体. 反应按双途径进行, 即按Eigen-Tamm机理进行的NRO^-途径和以质子迁移为速率控制步骤的两性离子途径. 两性离子的反应活性(以log kHL^±表示)与配体的碱性强度(pK2)之间呈现直线自由能关系. 并发现镍(II)配合物的离解反应速率常数(log k-L^-)与配体的碱性强度(pK2)和配合物的稳定常数(log KNiL^N^i)之间均存在直线自由能关系.

Linear free energy relationships between reaction rate constants and equilibrium constants of complex compounds II: Binary complex formation kinetics of N-(p-substituted phenyl) glycines with nickel (II)

The kinetics of the complexation reaction of some N-(p-substituted phenyl) glycines with Ni(II) at 25?and ionic strength 0.1 mol/dm3 in 30% (v) ethanol solution was studied by means of stopped-flow method. The experimental results showed that not only the ligand anion but also the zwitterion is an attacking species in the complexation reaction. The reaction takes place by way of 2 competing paths, one is the anion path which proceeds according to the Eigen-Tamm mechanism and another one is the zwitterion by which the rate-detg. step involves proton transfer. The reactivity of the zwitterions increased with decreasing basicity of the ligands. A linear free-energy relationship holds for all the reactions studied. Some linear free-energy relationships also exist between the dissociation rate constants and the basicity of the ligands and the stability constants of the binary complexes as well.