Metal Complexes with Macrocyclic Ligands. Part XXI. A nonlinear relationship between the stability of Cu2+ complexes and their complexation rate with 1,4,8,11‐tetraazacyclotetradecane

The kinetics of the reaction (1) between 1,4,8,11‐tetraazacyclotetradecane (Cy) and a series of Cu(II) complexes CuL (L) = glycolate, malonate, succinate, picolinate, glycinate, iminodiacetate, nitrilotriacetate, N‐(2‐hydroxyethyl)ethylenediaminetriacetate, ethyienediamine, 1,3‐diaminopropane, diethylenetriamine and N,N‐bis(3‐aminopropylamine) were studied spectrophotometrically at 25° and I = 0.5 (KNO3). From the analysis of the log kobs/log [L] profiles obtained at different pH values the resolved bimolecular rate constants k (Table 3) were obtained by a nonlinear curve‐fitting procedure. For nearly all systems studied, the rate constant k , describing the reaction between the 1:1 complex CuL and the monoprotonated form of the macrocycle CyH, was obtained. The nonlinear relationship between log k and log KCuL and its nature is discussed. It is shown that the inverse relationship between reactivity and stability described by others is only a special case of the more general Eqn. 3 described here.