The reductions of chloro-, bromo- and iodopentacyanocobaltate(III) anions by titanium(III) in aqueous acidic solution

Abstract

The reduction of chloro-, bromo-and iodopentacyanocobaltate(III) anions by aquatitanium(III) has been studied in aqueous solution with ionic strength, I = 1.0moldm -3 (LiC1, KBr or KI) at T= 25 ~ The dependence of the observed second-order rate constant, /Cobs, on IN +] has been investigated over the acid range 0.005-0.100 mol dm 3 and is of the general limiting form: kobs ~ ko + k[H +] 1, where k o is appreciable in all cases and k is a composite rate constant. Using values of K a (associated with the Ti m hydrolytic equilibrium constant), obtained from the kinetic data for the TiI"/Co nl redox reactions, and comparison of the rate constants obtained with those for the corresponding V II reductions of the same Co In complexes, it is concluded that the Ti m reductions of these halopentacyanocobaltate(III) complexes proceed via an outer-sphere mechanism.

Outer-Sphere electron-transfer and the effect of linkage isomerism in the titanium(III) reduction of nitro-pentacyanocobaltate(III) and nitro-, and nitrito-pentaamminecobalt(III) complexes in aqueous acidic media

“…Nonnegligible k 0 contributions were also observed in all the reductions of these oxidants by Ti III . Similar observations have been reported in the literature by earlier workers [1,[19][20].…”

“…The results agreed within 5%. The free acid concentration in the Ti III solution was determined as described by [16] and Ojo et al [1]. Analar grade LiCl and May and Baker grade HCl (36%, density 1.18g/cm 3 ) were used to prepare standardized solutions for maintaining ionic strength.…”

“…Its reductions of the cationic cobalt(III) complexes [Co(NH 3 ) 5 X] 2+ (X=Cl ) , Br ) , SO 4 2) ) have been shown to proceed by an outersphere mechanism, but the equivalent reaction for the fluoro complex proceeds by an inner-sphere mechanism [2]. Mechanistic studies on titanium(III) reduction of the cobalt(III) complexes, [Co(CN) 5 X] 2+ (X=F ) , Cl ) , Br ) ) were reported by Ojo et al [1] to proceed by outer-sphere mechanism.…”

“…Titanium(III) reductions of several metal complexes have been studied [1][2]. Its reductions of the cationic cobalt(III) complexes [Co(NH 3 ) 5 X] 2+ (X=Cl ) , Br ) , SO 4 2) ) have been shown to proceed by an outersphere mechanism, but the equivalent reaction for the fluoro complex proceeds by an inner-sphere mechanism [2].…”

Protonation of Chloro-, Bromo- and Iodo-pentacyanocobaltate(III) Complexes

“…After the report of Davies and Espenson on the reduction of these complexes by V II [6], a few workers have studied the reduction of these halo-pentacyano complexes by Ru II (O.T. Ayinde, unpublished work) and Ti III [7] in this laboratory. From all these previous works, the mechanism of the reduction of these complexes by various metal ions has been diagnosed.…”