H-AND CN--INDUCED DISSOCIATION OF NI2+-COMPLEXES WITH TETRA-N-SUBSTITUTE 1,4,8,11-TETRAAZACYCLOTETRADECANES()

The H+ and the CN- induced dissociation kinetics of the Ni2+ complexes with a series of tetra-N-substituted 1,4,8,11-tetraazacyclotetradecan es have been studied by spectrophotometry at 25 degrees C. The pH depe ndence of the H+ induced reaction follows the rate law v(1) = k(1)[NiL (2+)] + k(2)[NiLH(3+)], in which NiLH(3+) is a protonated species pres ent in equilibrium with NiL(2+) at pH values below 2. The rate constan t k(2) is larger than k(1) by a factor of 50-120, indicating that, whe n the complex is protonated, its tendency to dissociate is greatly inc reased. Both k(1) and k(2) are relatively insensitive to the nature of the N-alkyl groups. The CN- induced process is described by v(2) = k( 3)[NiL(CN)(+)][CN-], where NiL(CN)(+) is a ternary species rapidly and fully formed under the experimental conditions. The values of k(3) al so do not depend on the nature of the N-alkyl groups. A mechanisms con sidering different attack possibilities of CN- is discussed.