Iron(II) reduction of halogenocobalt(III) complexes of 3,8-dimethyl-5,6-benzo-4,7-diazadeca- 3,7-diene- 2,9-dione dioxime: Kinetics and mechanism

Abstract

The iron(II) reduction of cobalt(III) complexes of the type <em>trans-</em>[Co(DODOHbzo)(s-py)X]ClO₄<em>, </em>where DODOHbzo = 3,8-dimethyl-5,6-benzo-4, 7-diazadeca-3,7- diene-2,9-dione dioxime mono anion, s-py = pyridine (py), nicotinamide (nic-CONH₂) or isonicotin-amide (isonic-CONH₂) and X^- = Cl^-, Br^- or I^-, has been studied in DMSO/water (1%, v/v) at 27 ± 0.1°C and <em>I</em> = 0.25 mol dm^-3 (LiC1O₄) in the [H⁺] range 0.007-0.100 mol dm^-3 under pseudo-first order conditions using an excess of the reductant. The inverse dependence of rate on [H⁺] suggests an equilibrium between the protonated and unprotonated forms of the complex, the protonated from reacting slower than the unprotonated form. The rate constants reflected the trend Cl^- < Br^- < I^- and py < nic-CONH₂ iso-nic-CONH₂ for the axial ligands.