Cobalt(II) and cadmium(II) chelates with nitrogen donors and O2 bonding to Co(II) derivatives

The formation of Cd(II) and Co(H) complexes with N-methylethylenediamine (men) has been studied at 298 K in dimethylsulfoxide (dmso) in an ionic medium set to 0.1 mol dm(-3) with Et4NClO4 in anaerobic conditions by means of potentiometric, UV-Vis, calorimetric and FT-IR technique. Mononuclear MLj (M = Cd, Co; j = 1-3) complexes are formed in exothermic reactions, whereas the entropy changes oppose the complexes formation. The results are discussed in terms of different basicities and steric requirements and the whole of the thermodynamic data reported till now for the two ions with a number of diamines are summarized to visualize the selectivity of the ligands. The dioxygen uptake of Co(men)(2) species has also been studied by means of UV-Vis and EPR techniques. The kinetic parameters and stability constants obtained for the formation of the superoxo and mu-peroxo species are discussed in terms of solvent effect and steric hindrance due to methyl group. Cyclic voltammetry was used to confirm the stability constant for the Co(dmen)(2) (dmen = N, N'-diniethylethylenediamine) superoxo adduct formation but was not successful to investigate this Co(men)(2)-O-2 system. (C) 2004 Elsevier B.V. All rights reserved.