EFFECTS OF SUBSTITUENTS AND CHALCOGEN ATOMS ON THE REDUCTION HALF-WAVE POTENTIALS OF (SUBSTITUTED ETA-CYCLOPENTADIENYL)(1,2-SUBSTITUTED 1,2-ETHYLENEDICHALCOGENOLATO)COBALT(III) COMPLEXES IN ACETONITRILE SOLUTIONS

Twenty-six (substituted eta-cyclopentadienyl)(substituted 1,2-ethylenedithiolato)cobalt(III) complexes underwent Nernstian one-electron reduction at a platinum electrode in 0.1 mol dm-3 tetraethylammonium perchlorate + acetonitrile solutions at 25-degrees-C. Their reversible half-wave potentials were linearly dependent on the sum of the field parameters of the substituents. A substituent at the cyclopentadienyl ligand affects the half-wave potential to a larger extent than one at the dithiolato ligand does. The chemical shifts of cyclopentadienyl carbon and hydrogen atoms varied linearly with the half-wave potential when the substituents at the dithiolato ligand were changed. A linear relationship was found also between the half-wave potential and the chemical shift of dithiolene carbon atoms of the complexes having substituted cyclopentadienyl ligands. A substituent at one ligand affects the electron density at the other ligand through the central atom. The effects of substituents were almost additive. Six complexes in which the sulphur atoms were replaced by selenium were also reduced through a Nernstian one-electron reduction step, and the half-wave potential changed linearly with the number of selenium atoms. The effect of replacement of the chalcogen atoms was independent of the substituents at the two ligands.