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Kinetics and mechanism of electroreduction of ethylenediamine and hydroxyethylenediamine complexes of zinc(II) on a dropping-mercury electrode

“…The products of reduction of ethylenediamine complexes of zinc(II) that are responsible for the appearance of a polarographic peak probably included, along with zinc atoms, ligands. Similar regularities of the appearance of a polarographic peak were observed in the course of reduction of the ammonia and hydroxyammonia complexes of zinc(II) on DME at the overall concentration of ions of zinc(II) equal to 2 × 10 -5 M in more dilute solutions of supporting electrolytes [7].…”

“…The average value of the diffusion coefficient for different forms of complexes of zinc(II) that were present in the investigated solutions [8], which was calculated from the values presented in Table 1, amounts to (5.9 ± 1.1) × 10 -6 cm 2 s -1 at 25°ë and coincides, to within errors, with the value 6.45 × 10 -6 cm 2 s -1 , which we calculated for complexes Zn (0.1 M KNO 3 , 25°C) from the data reported in [9]. It must be mentioned that the values of the diffusion coefficient for complexes of zinc(II) containing ethylenediamine presented by us are considerably smaller than the value of the diffusion coefficient for complexes of zinc(II) containing ammonia, specifically, D = (1.0 ± 0.1) × 10 -5 cm 2 s -1 , which was determined at 25°C in [7]. This is probably due to larger dimensions of ethylenediamine complexes of zinc(II), which, as follows from [8], form associates with perchlorate ions at high concentrations of perchlorate ions.…”

“…nism of electroreduction of the ammonia and hydroxyammonia complexes of zinc(II), which is presented in [7]. As was established in [8], the formation of simple ethylenediamine complexes of zinc(II) in 1 M NaClO 4 solutions of pH 9.5-11.5 is accompanied by the formation of its mixed hydroxyethylenediamine complexes.…”

“…Processes of electroreduction of labile complexes of zinc(II) with various ligands include an electrochemical step and preceding reversible chemical steps, in which some ligands are abstracted with the formation of electrochemically active complexes that take part in a discharge step [1][2][3][4][5][6][7]. In particular, it was established that, in solutions of a high ionic strength, the electroreduction of ammonia [1][2][3][4][5][6][7] and hydroxyammonia [1,7] complexes of zinc(II) on zinc amalgam and a mercury electrode involves preliminary abstraction of some ammonia molecules and/or hydroxyl ions and the formation of complexes Zn , which take part in the slow electrochemical step.…”

“…In particular, it was established that, in solutions of a high ionic strength, the electroreduction of ammonia [1][2][3][4][5][6][7] and hydroxyammonia [1,7] complexes of zinc(II) on zinc amalgam and a mercury electrode involves preliminary abstraction of some ammonia molecules and/or hydroxyl ions and the formation of complexes Zn , which take part in the slow electrochemical step. In [7], a conclusion was drawn about an inner-sphere mechanism of a two-electron electrochemical step involving complexes Zn . Information on the electron transfer in the course of reduction of other complexes of zinc(II) is in short supply.…”