Kinetics and equilibria for complex formation between palladium(II) and chloroacetate

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 . dm(-3) HClO4 at 298.2 K. The equilibrium constant, K, of the reaction Pd2+ + HL reversible arrow PdL+ + H+ was determined from multi-wavelength absorbance measurements of equilibrated solutions at variable temperatures as log(10)K (298.2K) = 0.492 +/- 0.006 with Delta H-o = - 15.6 +/- 1.9 kJ . mol(-1) and Delta S-o = -43.0 +/- 6.3 J . K-1, mol 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 . dm(-3) as k(1) = 6.46 +/- 0.08 dm(3) . mol(-1) . s(-1) and k(-1) = 2.91 +/- 0.03 s(-1), with activation parameters Delta H-1(not equal) = 56.55 +/- 0.75 kJ . mol(-1), Delta S-1(not equal) = -40.0 +/- 2.5 J . K-1 mol(-1), Delta H--1(not equal) = 64.42 +/- 0.50 kJ . mol(-1) and Delta S--1(not equal) = -20.3 +/- 1.7 J . K-1 . mol-1, respectively. From the kinetics of the forward and reverse processes, log(10) K = 0.346 +/- 0.007, Delta H-o = -7.9 +/- 0.9 kJ . mol(-1) and Delta S-o = - 19.8 +/- 3.0 J . K-1 . mol(-1) were derived, and these values are in good agreement with the results of the equilibrium measurements. The Specific Ion Interaction Theory was employed for determination of thermodynamic equilibrium constants for the protonation of chloroacetate (log(10) K-p(o) = 2.857 +/- 0.016) and formation of the PdL+ complex (log(10) K-o = 1.002 +/- 0.046, log(10) beta(o) = 3.859 +/- 0.048). Specific ion interaction coefficients epsilon(L-, Na+) = 0.042 +/- 0.022 kg . mol(-1), epsilon(L-, K+) = 0.081 +/- 0.021 kg . mol(-1), epsilon(PdL+, ClO4-) = 0.92 +/- 0.21 kg . mol(-1) were derived.