Metal complexes with macrocyclic ligands. Part XX. Influence of coordinated ligands onto the complexation rate of Ni2+ with 1,4,8,11-tetraazacyclotetradecane

The kinetics of the reaction between 1,4,8,11-tetraazacyclotetradecane (Cy) and Ni²⁺ in the presence of series of ligands L = fluoride, acetate, glycolate, oxalate, malonate, succinate, methanetriacetate, 1,3,5-cyclohexanetriacetate, tricarballylate, picolinate, glycinate, iminodiacetate, nitrilotriacetate. N,N′ -ethylenediiminodiacetate, ammonia, pyridine, ethylenediamine, 1,3-propanediamine and diethylenetriamine were studied by pH-static and spectrophotometric methods at 25° and I = 0.5. By analysis of the log k/log L] and/or log k/pH profiles the resolved bimolecular rate constants K (Table 3) were determined using a non-linear least-square fitting procedure. Practically for all systems the rate constant K, describing the reaction between the 1:1 Ni²⁺ complex and the monoprotonated form of the macrocycle, was obtained. In some cases, however, also K and K were found. Since the experimental conditions were choosen so that NiL was mainly formed, the reactivity of NiL₂ was generally not measurable. The effect of the number of coordinated donor groups in NiL and of the charge of NiL on K is discussed. Both effects seem to indicate that for the reaction between NiL and CyH⁺ first bond formation is not the rate-determining step.