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