Studies on the Polarographic Behaviour of Bis(Ethylenediamine)-Copper(II) Ion and Bis(Glycinato)Copper(II) and the Rates of their Electro-Reduction

Inorganic Chemistry Laboratories,
Chemistry Department, University College of Science, Calcutta-9

Department of Inorganic Chemistry,
Indian Association for the Cultivation of Science, Calcutta-32.
Received 4 September 1972

In aqueous KNO₃ mediurn (with 0.01% gelatin) bis(ethylenediamine)copper(II) ion, Cu(en)₂²⁺, and bis(glycinato)copper(II), Cu(gly)₂, undergo one-step irreversible reduction Cu^II  \(\to\) Cu⁰at the D.M.E. The effect of the salt medium on the E_1/2 of Cu(en)₂²⁺ seems to suggest ion-association. The effect of 'free ligand' in solution on the nature of the wave has also been studied for both the complexes. From the characteristics of the irreversible wave the rate constant, k_r, for the electro-reduction of each complex was
evaluated at a reference potential of -0.7 V vs. SCE, and from the k_r values at three different temperatures the corresponding activation energies, E_a, were also evaluated. It has been observed that Cu(gly)₂ with a lower wave number of the principal ligand field band is more readily reduced (as shown by less negative E_1/2,higher value of k_r and lower value of E_a) than Cu(en)₂²⁺. A plausible mechanism of electron transfer from the electrode to the Cu^_II in the complex has been suggested which explains this observation.