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

The complexation property and the acid dissociation kinetics of four N,N'-d ialkyl-1,10-phenanthroline-2,9-dimathanamine complexes with cobalt(II) were studied using a pH meter and a stopped-flow spectrophotometer. In 6.6 x 10 (-3)similar to 0.5 mol dm(-3) HCl (I = 0.5 mol. dm(-3) HCl + NaCl), the dis sociation rate follows the law k(obs) = kK(2)[H+]/(1 + K-2[H+]). The acid d issociation can be rationalized in terms of a four-step kinetic process inv olving two rapid pre-equilibrium protonations and rate-determining cleavage of the Co(II)-N(phenanthroline) bond. The temperature dependence of the ra te was determined, and the appropriate thermodynamic parameters were obtain ed. The linear relationship between Delta H-not equal and Delta S-not equal suggests that an isokinetic temperature, T-iso of 282 +/- 2 K exists.