Metal Complexes with Macrocyclic Ligands, V. Formation and dissociation kinetics of the pentaco‐ordinated Ni²⁺, Cu²⁺, Co²⁺ and Zn²⁺ complexes with 1,4,8,11‐tetramethyl‐1,4,8,11‐tetraazacyclotetradecane

Abstract

Abstract The formation and dissociation kinetics of the pentaco‐ordinated Cu 2+ , Ni 2+ , Co 2+ and Zn 2+ complexes with 1,4,8,11‐tetramethyl‐1,4,8,11‐tetraazacyclotetradecane (4‐MeCyclam‐14) was studied by pH‐stat techniques and spectrophotometrically. The rates of the reactions between 4‐MeCyclam‐14 and each of the four metal ions, although slower than normal complexations by a factor of 10 3 −10 4 , closely follow the order Cu 2+ > Zn 2+ > Co 2+ > Ni 2+ , found for the rate of water exchange. This implies that beside water exchange an other constant factor plays an important role in the rate determing step. The dissociation of the pentaco‐ordinated 4‐MeCyclam‐14 complexes is acid catalyzed. The limiting rate for acid dissociation is not reached even in 2.5 M HNO 3 in the case of Ni(4‐MeCyclam‐14) 2+ . From the formation and dissociation rates stability constants have been calculated, which do not show any macrocyclic effect.