Reduction kinetics of glycinate complexes of palladium(II) on a dropping-mercury electrode in acid perchlorate solutions

Polarograms for the reduction of glycinate complexes of palladium(II) (5 × 10^?5 M) are obtained in equilibrium solutions of pH 0.8–3.0 with different protonated-glycine concentrations c _Hgly (supporting electrolyte, 0.5 M NaClO₄). It is established that the irreversible wave of reduction of complexes Pd(gly)₂ corresponds to the diffusion limiting current I _d ⁽²⁾ . A similar wave at pH 1.5 and c _Hgly = 0.005 M, as well as at pH 1.0 and c _Hgly = 0.05–0.5 M is preceded by the diffusion limiting current I _d ⁽¹⁾ . Values of the I _d ⁽²⁾ /I _d ⁽¹⁾ ratio are close to the ratio between equilibrium concentrations of Pd(gly)₂] and Pdgly⁺], calculated using the step stability constant for Pd(gly)₂. This fact testifies to the reduction of complexes Pdgly⁺ in the vicinity of I _d ⁽¹⁾ and complexes Pd(gly)₂, in the vicinity of I _d ⁽²⁾ . At pH 0.8–1.2 and H₂gly⁺] = 1 × 10^?4 to 5 × 10^?3 there is observed the diffusion-kinetic limiting current of the first wave I ₁ ⁽¹⁾ , which increases with increasing H⁺] and decreasing H₂gly⁺]. The nature of the slow preceding chemical stage that occurs during the reduction of complexes Pdgly⁺ is discussed.