Reactions of µ-hydroxo dicobalt complexes. Part VI. Equilibrium and kinetic studies on the reaction of chloride ions with the µ-amido-µ-hydroxo-bis[tetra-amminecobalt(III)] complex

Abstract

LS2 9JTThe cleavage of the hydroxo-bridge of the p-amido-p-hydroxo-bis[tetra-amminecobalt(iii)] complex by chloride ions in aqueous perchloric acid solutions, p = 2 . 0 ~ (NaCIO,), has been studied. From spectrophotometric studies at 554 nm, [CI-] = 0 . 2 -0 . 5 ~ and [H+] = 0.3 -2 . 0 ~~ the equilibrium constant K f o r (i) at 25" is 10.6 f 1.4 la mol-2. keq(s-l) = kl[H+] [CI-] + k2[CI-] + kbwhere data for the back reaction k,, have been reported previously. At 25" kl = 9 . 6 (f 0.2) x I O-* l2 mol-2 s-l,and k1/k-, = 11.9 f 0-6 la mol-2, where the latter is in satisfactory agreement with the above value of K. From the temperature dependences AHl$ = 1 6 . 2 f 0.5 kcal mol-l, ASIS = -1 8.1 f 1 a 8 e.u., AH2$ = 25.0 f 3.9 kcal mol-l and AS2$ = 7.4 h 12.7 e.u. The further reaction with a second chloride (ii) is effective [CI-] > 0 . 5 ~. At 25" K3 = 0.09 f 0.04 I mol-l, and from equilibration studies k3 -9 x I mol-l s -l and k-, = 2.2 x Rate constants keg for the equilibration in (i) can be expressed, s-1 at 1.5".THIS paper is one of a series in which the kinetics and thermodynamics of interconversion reactions of pamido (ammine) binuclear complexes of cobalt (111) are considered.1 The present investigation is primarily concerned with the interconversion of the p-amido-phydroxobis[tetra-amminecobalt ( III)] and v-amido-[aquotetra-amminecobalt (III)] [chlorotetra-amniine 1 Part v of this series is M. B. Stevenson, A. G. Sykes, and R. S. Taylor, J . Chem. SOC. (A), 1970, 3214. cobalt(~~~)]complexes, (l), hereafter referred to as the p-amido-p-hydroxo-and aquo-chloro-complexes respectively. The kinetics of the back reaction, kb, have been reported previously.2 It has also been possible to obtain data for the subsequent equilibrium, (2), in which the bischloro-complex is formed. The studies are confined to solutions with [H+] and [Cl-1 in the range

The uncatalysed and mercury(II)- and thallium(III)-catalysed elimination of chloride from the µ-amido-µ-chloro-bis[tetra-amminecobalt(III)] complex

“…The ionic strength in the present study was adjusted with NaClO,, which has previously been shown to give satisfactory agreement with runs in which LiC10, was used. 25 The sodium perchlorate was shown to contain 0.02% of chloride, by titration with silver nitrate. Such an amount is negligible as far as this study is concerned.…”

Mechanism of hydroxo-bridge cleavage in dicobalt(III) complexes

“…The case for a limiting SnI mechanism has also been examined. The reaction sequence may be expressed as in ( 9)-(l 1), where kx includes the initial protonation equilibrium (11) step. Assuming stationary-state kinetics for the five-coordinate intermediate k may be expressed as in (12).…”