Kinetics and mechanism of oxidation of thiosulphate by the complex ion [Mn-3(IV)(mu-O)(4)(phen)(4)(H2O)(2)](4+) (phen=1,10-phenanthroline) in weakly acidic aqueous media
D. Maji et R. Banerjee, Kinetics and mechanism of oxidation of thiosulphate by the complex ion [Mn-3(IV)(mu-O)(4)(phen)(4)(H2O)(2)](4+) (phen=1,10-phenanthroline) in weakly acidic aqueous media, TRANSIT MET, 26(4-5), 2001, pp. 544-550
The trinuclear complex ion [Mn-3(IV)(mu -O)(4)(phen)(4)(H2O)(2)](4+) (1) is
quantitatively reduced by an excess of S2O32- to Mn-II, but the binuclear
complex [(MnMnIV)-Mn-III(mu -O)(2)(phen)(4)](3+), (2) is the only manganese
product when [S2O32-] = 1.5 [(1)]. With an excess of S2O32- biphasic kinet
ics, (1) (k(1)(0)) under right arrow (2) (k(2)(0)) under right arrow Mn-II
is observed, while the reaction with S2O32- = 1.5 [(1)], follows one-step s
econd order kinetics with the second order rate constant k = k(1)(0)/[S2O32
-]. The rate constant k(1)(0) is independent of c(phen) ( = [phen] + [Hphen
(+)]) but directly proportional to [H+] and [S2O32-]. Rapid formation of an
adduct between (1) and S2O32-, followed by rate-determining one-electron,
one-proton reduction of the adduct, appears logical. A comproportionation r
eaction in one of the subsequent rapid steps leads to (2) without any Mn-II
co-product. Kinetic dependences for the second step are same to those for
an authentic complex of (2), and further support the assigned reaction sequ
ence.