Metal Complexes with Macrocyclic Ligands. Part XXI . A nonlinear relationship between the stability of Cu 2+ 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 (KNO 3 ). From the analysis of the log k obs /log [L] profiles obtained at different pH values the resolved bimolecular rate constants k   CyH   nCuL   m(Table 3) were obtained by a nonlinear curve‐fitting procedure. For nearly all systems studied, the rate constant k   CyH CuL , 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   CyH CuLand log K CuL 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.