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The interaction between molecular oxygen and the metal atom in two Co(II) complexes with bis(diacetylmonoxime-imino)propane-1,3 ( A ) and with the related ligand obtained from cobaloxime by substitution of both the O-H ⋯ O bridges with the -BF 2 -group ( B ) is investigated using electrochemical and spectroelectrochemical techniques. Notwithstanding the stability of the Co(II) complex B in air, the results suggest the formation of a dioxygen adduct as an unstable intermediate in the electrocatalytic reduction of molecular oxygen in the presence of either A or B . Furthermore, the oxygenation ratio at a given p O 2 appears to be quite different for the homogeneous reaction of A in the Co(II) oxidation state in bulk as compared with either the electrogenerated Co(II) (from complex A ) on the electrode surface or the Co(II) complex B .

The results of an investigation of the electrochemical behaviour in dimethyl sulphoxide (DMSO) and aqueous solution of the two new halogen-DMSO complexes Na[ trans -RuCl 4 (DMSO) 2 ] (I) and mer -RuCl 3 (DMSO) 3 (II) are presented. Both complexes give trans -RuCl 2 (DMSO) 4 upon bulk one-electron reduction of their DMSO solutions. In DMSO solution, complex II equilibrates with a less easily reducible isomer differing in the mode of binding of one DMSO ligand. This equilibrium, together with the homogeneous chemical reactions following the heterogeneous mono-electronic reduction of II, was estimated quantitatively by means of cyclic voltammetry. Cyclic voltammetry of I in aqueous medium shows the occurrence of an H 2 O/DMSO exchange reaction following its one-electron reduction at a Pt microelectrode. The complete scheme of the reactions which characterize the bulk electrolysis behaviour of the two complexes in aqueous medium is also reported.