Kinetics and mechanism of oxidation of tris-(1,10-phenanthroline)iron(II) by chlorine and bromine and of the reduction of tris-(1,10-phenanthroline)iron(III) by iodide ions

Abstract

JIDE IGE, J. FOLORUNSO OJO, and OLUSEGUN OLUBUYIDE. Can. J. Chem. 57.2065Chem. 57. (1979. The rates of the oxidation of tris-(1,lO-phenanthroline)iron(II) by chlorine and bromine, and of the reduction of tris-(1,lO-phenanthroline)iron(III) by iodide ions have been measured at ionic strength I = 1.0 mol dm-3 (LiCIO,). All the reactions obey second-order rate law:The activation parameters for the reactions are: Fe(Phen)32+/Br,: AH* = (64.2 + 3.2) kJ mol-', AS* = -(24.9 + 1.5) J mol-' K-'. Fe(Phen)33+/I-:AH* = (39.8 t 2.1) kJ mol-', AS* = -(19.7 + 0.8) J mol-I K-'.The reactions of tris-(1,lO-phenanthroline)iron(II) with chlorine and bromine are unaffected by chloride, bromide, and acid. The proposed mechanism for these reactions involves a series of one-electron changes, with the species X,-(X = CI, Br) as reaction intermediates, since good linear free energy correlations for the primary step, resulting in the formation of X2-, are obtained. The reduction of tris-(1,lO-phenanthroline)iron(III) by iodide ions is catalysed by bromide and chloride ions, whereas the reduction of aquoiron(II1) by iodide ions is known to be inhibited by bromide and chloride ions. A mechanistic interpretation of this observation is suggested. [Traduit par le journal]

Oxidation of Coordinated Ammonia to Nitrosyl in the Reaction of Aqueous Chlorine with cis-[Ru(bpy)2(NH3)2]2+

“…By way of comparison, the only other reported reaction of Cl 2 with substitution-inert transition-metal complex having no vacant coordination sites is that with [Fe(phen) 3 ] 2+ . 48,49 A 460-fold lower rate constant is reported for the reaction of Cl 2 with [Fe-(phen) 3 ] 2+ (2.4 M -1 s -1 ), which is qualitatively in agreement with expectations based on the greater thermodynamic barrier for this reductant. Detailed calculations in terms of Marcus theory would be of interest, but they should be deferred until a reliable potential for the Cl 2 /Cl 2 -couple becomes available.…”

Thermal and Photochemical Reduction of Aqueous Chlorine by Ruthenium(II) Polypyridyl Complexes

“…In view of the stoichiometry, rate law, and known substitution-inert character of the various complex reductants investigated in this study, it is reasonable to assign an outer-sphere electron-transfer mechanism to the k th step for all of them. A similar mechanism has been assigned in the literature reports on the reactions of chlorine with [Fe(phen) 3 ] 2+ and [Ru(bpy) 2 (NH 3 ) 2 ] 2+ . − Accordingly, Table collects the values of k th for these reactions along with the corresponding E ° values pertaining to the reductants. As is shown in Figure , there is a linear relationship between log k th and E ° for these reactions, which lends further support to the concept that they all have the same mechanism.…”

“…Unfortunately, the complex effects of [H + ] were not included in the analysis of the V(V) inhibition. The roster of coordination complexes oxidized by chlorine includes cis -[Ru(bpy) 2 (NH 3 ) 2 ] 2+ , [Fe(phen) 3 ] 2+ , , [Ni II (CN) 4 ] 2- , and [Pt II (CN) 4 ] 2- . Only for the first two of these complexes can an outer-sphere mechanism be assigned unambiguously, and of these two the reaction of cis -[Ru(bpy) 2 (NH 3 ) 2 ] 2+ is complicated by further oxidation of the NH 3 ligand.…”

Ion-pair formation in the outer-sphere electron transfer reactions between tris-(1, 10) phenanthroline iron(II) and the halopentacyanocobaltate(III) complexes in aqueous acidic solutions

“…They are very stable and inert, low-spin t 2 g 6 complexes [1][2][3]. Reactions of Co(CN) 5 X 3À (X = Cl, Br or I) with Ti(III) [4], V(II) [5] and Ru(II) (O. T. Ayinde, unpublished work) have been investigated and concluded to proceed by an outer-sphere mechanism since k sub < <k e.t .…”