The Kinetics of Complexation of Nickel(II) and Cobalt(II) Mandelates in Aqueous Solution

The Kinetics of Complexation of Nickel(II) and Cobalt(II) Mandelates in Aqueous Solution

The rate constants for the formation and dissociation of nickel(II) and cobalt(II) complexes with mandelate have been determined by the pressure-jump relaxation study. The forward and reverse rate constants for the mandelate complex formation reactions were obtained to be $k_f=3.60{\times}10^4\;M^{-1}s^{-1}$ and $k_r=1.73{\times}10^2\;s^{-1}$ for the nickel(II), and $k_f=1.75{\times}10^5\;M^{-1}s{-1}$ and $2.33{\times}10^3\;s^{-1}$ for the cobalt(II) in aqueous solution of zero ionic strength ($(\mu{\to}0)\;at\;25^{\circ}C$. The results were interpreted by the use of the multistep complex formation mechanism. The rate constants evaluated for each individual steps in the multistep mechanism draw a conclusion that the rate of the reaction would be controlled by the chelate ring closure step in concert with the solvent exchange step in the nickel(II) complexation, while solely by the chelate ring closure step for the cobalt(II) complex.