Ligand influence on the electrochemical behavior of some copper(II) thiosemicarbazone complexes

The redox properties of the title mono- and binuclear copper(II) chelates have been investigated by cyclic voltammetry in DMF at a working platinum electrode. The cathodic reduction and anodic oxidation of the investigated chelates produced the corresponding electrochemical Cu-I and Cu-III species stable only in the voltammetric time scale, The effects of substituents on E-1/2, redox properties and stability towards oxidation of the complexes were related to the electron-withdrawing or releasing ability of the substituents on the C=N-1 [H, CH3 or C6H5] and/or (NH)-H-4 [H, C2H5, C6H5 or pClC(6)H(4)] groups, The electron attracting substituents stabilize the Cu(II) complexes while electron-donating groups favor oxidation to Cu(III). Changes in the E-1/2 for the complexes due to remote substituent effects could be related to changes in basicity of (NH)-H-4. Thus, variation in N(4)1-J has more influence on E-1/2 than changes in C=N-1. The correlation between E-1/2 of the complexes and pK(a) of the ligands has been attributed to the spherical potential generated by the electron density of the donor atoms at the antibonding d orbitals.