Voltammetric lability of multiligand complexes: the case of ML2

Abstract

The voltammetric lability of a complex system, where a metal ion M and a ligand L form the species ML and ML 2 , is examined. Together with the rigorous numerical simulation of the problem, two limiting cases are analysed for the overall process ML 2 ! M: (i) the most common case for aqueous complexes, where ML ! M is the kinetically limiting step and (ii) the case where ML 2 ! ML is limiting. In both cases, analytical expressions for the lability criteria are provided which show good agreement with the results obtained from the rigorous numerical simulation of the problem.

Stripping chronopotentiometry at scanned deposition potential (SSCP). Part 7. Kinetic currents for ML2 complexes

“…Data are presented for 1:2 Cd(II) complexes with iminodiacetic acid (IDA) and N-(2-hydroxyethyl)iminodiacetic acid (HIMDA), and for Cd(II) and Zn(II) complexes with pyridine-2,6-dicarboxylic acid (PDCA). The experimental data are shown to be in satisfactory agreement with the recently established lability criteria for both a macroscopic electrode and a microelectrode [4].…”

“…Thus, if there is dynamic equilibrium between M and ML, i.e. the rate constants for the volume reactions are fast on the experimental timescale, t, such that k 0 a1 t; k d1 t ) 1, then, to an even greater extent, this also holds true for the equilibrium between ML and ML 2 ðk 0 a2 t; k d2 t ) 1Þ and so forth [4]. That is conversion of, e.g., ML 2 into ML, and vice versa, is faster than interconversion of M and ML, and consequently the step ML !…”

“…Until now, lability criteria had been established only for 1:1 ML complexes. Recent work [4] has explored the case for ML 2 complexes, and reported analytical expressions for the kinetically limiting cases in the overall process ML 2 ! M, i.e., ML !…”

Effect of tartaric acid in the electrodeposition of zinc

“…In such systems, the shape of the voltammetric response depends on the voltammetric lability of metal complexes [15][16][17] . From these equilibria, the electrochemical process can be represented by the following scheme:…”

Determination of Zn2+ concentration with AGNES using different strategies to reduce the deposition time

“…So, for a fixed Y, the required concentration of M°decreases, as well as the number of moles needed inside the mercury electrode, parallel to the decrease in c à M . However, it is well-known [21][22][23][24][25][26][27][28][29] that the dissociation of complexes along the diffusion layer can play a very relevant role in the transport of the metal ions towards the electrode. Thus, in the successive metal-to-ligand ratios of a titration, the contribution of the complexes to the flux of metal towards the electrode reduces the required time practically to reach the target [30], especially if most of the metal is present as non-inert complexes.…”