AbstractThe complexation kinetics of 2,6,9, 13‐tetraazatetradecane(1), 1,4,8, 11‐tetraazacyclotetradecane(2)andN,N′,N″,N'‐tetramethyl‐1,4,8, 11‐tetraazacyclotetradecane(3)with Ni2+were studied by the stopped‐flow technique in DMSO and DMF. The biomecular rate constants kLNi(Table 2) follow in both solvents the order1≳2>3.The similar complexation rates of1and2in their unprotonated form indicate that for both the open chain and the cyclic ligand the same mechanism holds. By comparison with the solvent exchange the rate determining step of the complexation is the dissociation of the first solvent molecule in the outer‐sphere complex. The lower reactivity of3is probably due to steric effects.In the case of2a second step in the complexation process was observed and explained by a rearrangement of the ligand already coordinat