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Diaquocobaloxime and three other chelating ligands obtained by substitution of the O ⋯ H ⋯ O bridge with (CH2)3 or BF2 groups have been examined in order to compare the effects of changes in the in-plane ligand on the relative stability of different oxidation states of the cobalt atom and on the cis-effect of the equatorial structure with those observed in the corresponding organometallic derivatives. The cis-effect of the in-plane ligand was evaluated from the electrochemistry of the CoIII/CoII electron transfer which is dependent upon the Co-solvent bond strength changes in the axial positions. The axial interaction depends mainly on the nature of the axial ligand. The introduction of either one (CH2)3 group or two BF2 groups or both leads to a displacement of the stability range of the CoII oxidation state towards more anodic redox potentials. The (CH2)3 group appears to be more effective both in the displacement of the redox potential and in teh bathochromic shift of the visible band at 450–500 nm of the CoII chelates.

Some new derivatives of organocobaloximes containing para -substituted diphenylboryl groups, RCo(DH) 2− n (DB( p- XPh) 2 ) n L (R=alkyl or aryl group, L= N -MeIm, Py or H 2 O, X=OCH 3 , CH 3 or Cl, n =1 or 2) have been synthesized. The X-ray structures and the 1 H-NMR spectra are compared with those of the corresponding RCo(DH) 2− n (DBPh 2 ) n L and RCo(DBF 2 ) 2 L complexes. The insertion of X groups in the phenyl rings does not significantly affect the equatorial CoN distances, whereas the CoPy distances increase slightly in the order (DB( p- OCH 3 Ph) 2 ) 2 p- ClPh) 2 ) 2 2 ) 2 . 1 H-NMR spectra suggest that the conformational distribution in solution is similar to that observed in the corresponding BPh 2 derivatives. Electrochemical studies on the corresponding MeCo(DB( p- XPh) 2 ) 2 H 2 O compounds show a mono-electron Co(III)/Co(II) transfer reaction followed by two parallel reactions: (a) mono-electron Co(II)/Co(I) transfer; (b) homolytic dissociation of the CoC bond with the formation of Co(I) species, the relative rates of the two processes being dependent on X. As the electron-withdrawing power of the equatorial ligand increases, the reduction potentials associated with both Co(III)/Co(II) and Co(II)/Co(I) processes shift towards more positive values, indicating a decrease of electron density on the Co atom. The effects are comparable with those observed by changing the axial ligands.

Electrocatalysis of dioxygen reduction to superoxide ion in dimethylformamide is afforded by a reversible interaction with thiol or hydroxo forms of pyrimidine which takes place only on the mercury surface electrode even in the absence of transition metal ions. The interaction is revealed by a polarographic wave and by a voltammetric peak which can be recorded only in the presence of dioxygen in the pyrimidines solution. The polarographic wave and voltammetric peak are attributed to the reduction of the oxygenated pyrimidine. In the range of concentration where the polarographic limiting currents due to the reduction of the oxygenated and unoxygenated pyrimidine are of the same order of magnitude, the stoichiometric ratio dioxygen/pyrimidine is determined to be 1. The electrode process probably involves the formation of a complex of mercury with the thiol or the hydroxo form of the pyrimidine on the electrode surface. Adsorption or coadsorption of the reactants seems to be involved.

A series of binuclear complexes of the type [(μ-OH)(RCoIIIL)2]+ were L is the tridentate 2-(2-pyridylethyl)imino-3-butanone oximato ligand and R = Me, Et, CH2CF3, CH2Cl or Cy have been prepared and characterised. Some of their physico-chemical properties, namely the Co–R bond lengths, the νCo–Me Raman frequencies and the E1/2 half-wave potentials of the one-electron reduction process have been determined. Comparison of these properties with those of the metalloorganic derivatives containing tetradentate ligands, such as cobaloximes, Costa model derivatives and cobalamins, suggests that in the present compounds the Co–C bond strength and the electrochemical behaviour are more influenced by electronic than by steric factors.