Kinetics and Equilibria for Complex Formation between Palladium(II) and Chloroacetate

Abstract

Kinetics and equilibria for the formation of a 1:1 complex between palladium(II) and chloroacetate were studied by spectrophotometric measurements in 1.00 mol\(\cdot {\rm dm}^{-3}\) HClO4 at 298.2 K. The equilibrium constant, K, of the reaction $$ {\rm Pd}^{2 + } + {\rm HL}^{K} {\rm PdL}^+ +{\rm H}^+ $$ was determined from multi-wavelength absorbance measurements of equilibrated solutions at variable temperatures as log\(_{10} \, K (298.2\,K) = 0.492 \pm \) 0.006 with \(\Delta H^{\circ}=-15.{6}\pm 1.{9} \,{\rm kJ} \cdot {\rm mol}^{-1}\) and \(\Delta^{\circ}=-43.{0}\pm 6.{3} {\rm J} \cdot {\rm K}^{-1} \cdot {\rm mol}^{-1}\), and spectra of individual species were calculated. Variable-temperature kinetic measurements gave rate constants for the forward and backward reactions at 298.2 K and ionic strength 1.00 mol\( \cdot\,{\rm dm}^{-3}\) as \(k_{1}=6.46\pm 0.08 {\rm dm}^{3} \cdot {\rm mol}^{-1} \cdot {\rm s}^{-1}\) and \(k_{-1}=2.91\pm 0.03 {\rm s}^{-1}\), with activation parameters \(\smash{\Delta H_1^{\ne} = 56.55 \pm 0.75 } {\rm kJ} \cdot {\rm mol}^{-1}, \smash{\Delta S_1^{\ne} = - 40.0 \pm 2.5} {\rm J}\cdot {\rm K}^{-1} \cdot {\rm mol}^{-1}, \smash{\Delta H_{ - 1}^{\ne} = 64.42 \pm 0.50 } {\rm kJ} \cdot {\rm mol}^{-1}\) and \(\smash{\Delta S_{ - 1}^{\ne} = - 20.3 \pm 1.7} {\rm J} \cdot {\rm K}^{-1} \cdot {\rm mol}^{-1}\), respectively. From the kinetics of the forward and reverse processes, \(\log _{10} \,K = 0.346 \pm 0.007, \Delta H^{\circ}=-7.9\pm 0.9 {\rm kJ} \cdot {\rm mol}^{-1}\) and \(\Delta^{\circ}=-19.{8}\pm 3.{0} {\rm J}\cdot {\rm K}^{-1} \cdot {\rm mol}^{-1}\) were derived in good agreement with the results of the equilibrium measurements. Specific Ion Interaction Theory was employed for determination of thermodynamic equilibrium constants for the protonation of chloroacetate (\(\log _{10} \,K^\circ _ {\rm p} = 2.857 \pm 0.016 \)) and formation of the PdL+ complex (\(\log _{10} K^\circ = 1.002 \pm 0.046, \log _{10} \beta^\circ = 3.859 \pm 0.048\)). Specific ion interaction coefficients \(\varepsilon({\rm L}^{-},{\rm Na}^{+})=0.04{2}\pm 0.02{2} {\rm kg}\cdot {\rm mol}^{-1}, \varepsilon({\rm L}^{-},{\rm K}^{+})=0.08{1}\pm 0.02{1} {\rm kg}\cdot {\rm mol}^{-1}, \varepsilon ({\rm PdL}^+ ,{\rm ClO}_4^-) = 0.92 \pm 0.21 {\rm kg}\cdot {\rm mol}^{-1}\) were derived.