EPR spectral and redox properties of some 2,9-dimethyl-1,10-phenanthroline copper(II) complexes

The redox behaviour of [Cu(dMP)(2)](ClO4)(2) (1), [Cu(dmP)(2)]SO4 (2), [Cu(dmp)(2)Cl]Cl.H2O (3) and [Cu(dmp)(2)Br]Br.H2O (4) has been investigated in 50% aqueous-ethanol/0.2 M NaClO4 and absolute ethanol/TBAP at GCE by means of cyclic voltammetry. All these complexes show a quasi-reversible Couple Cu2+/+ with formal potential, E-0' = +430 to +650 mV vs SCE in the potential range +1.0 to -0.2 V vs SCE. Analysis of CV data shows that the electrode process for complex 3 involves ECE mechanism in absolute ethanol/0.1 M TBAP medium. An unusual and complicated electrochemical behaviour has been observed for this complex in 50% aqueous-ethanol/0.2 M NaClO4 medium due to the presence of more than one complex species in solution. The reduction potentials, E-pc1 (Cu2+/+) for complexes 2 and 4 in 50% aqueousethanol medium are almost similar at a given scan rate. However, the ease of reduction decreases (i.e. E-pc1 becomes less positive) in the order : 1 > 4 > 3 in absolute alcohol/0.1 M TBAP medium. Powdered and frozen solution EPR spectra (77 K) of these complexes have also been studied and the results are interpreted.