The iron(II) reduction of cobalt(III)-dioxime complexes of the typetrans-[Co(DODOHbzo) (s-py)X]ClO4, where DODOHbzo=3,8-dimethyl-5,6-benzo-4,7-diazadeca-3,7-diene-2,9-dione dioximate (1−), s-py=pyridine (py), nicotinic acid (nic-COOH) or isonicotinic acid (isonic-COOH) and X−=Cl−, Br− or I−, was studied in 1% (v/v) DMSO-H2O at 27±0·1°C andI=0·25M (LiClO4) in the [H+] range 0·007–0·100M 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 form reacting slower than the unprotonated one. The rate constants reflect the trend Cl−<Br−<I− and py<nic-COOH≃isonic-COOH for the axial ligands.
Volume 135, 2023
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