Kinetic and equilibrium studies of the acid dissociation of the zinc(II) complexes of N,N '-dialkyl-1,10-phenanthroline-2,9-dimethanamine ligands

The complexation property and the acid dissociation kinetics of the zinc(II ) complexes of N,N'-dialkyl-1, 10-phenanthroline-2,9-dimethanamine ligands have been studied using pH-metric and a stopped-flow spectrophotometer. In 3.3x10(-3)similar to1.2x10(-2) mol dm(-3) HCl (I=0.5 mol dm(-3), HCl+NaCl), the dissociation rate follows the law k(obs)=kK' [H+]. The acid dissociati on can be rationalized in terms of four-step kinetic process involving two rapid pre-equilibrium protonations and rate-determining cleavage of the Zn( II)-N(phenanthroline) bond. Steric effects on the stability of complexes an d on the kinetic process have also been discussed.