Abstract
The oxidation of [Cr
III
(HNTA)(Hist)(H
2
O)]
−
and [Cr
III
(HNTA)(Asp)(H
2
O)]
−
(NTA = nitrilotriacetate, Hist =
l
-histidinate and Asp =
dl
-aspartate) by periodate in aqueous medium has been studied spectrophotometrically between 15.0 and 35.0 °C under pseudo-first-order conditions, [IO
4
−
] ≫ [complex]. The rate increases over the pH range 3.40–4.45 in both cases, but the two complexes give different rate laws. It is proposed that electron transfer proceeds through an inner-sphere mechanism via coordination of IO
4
−
to chromium(III). A common mechanism for the oxidation of some chromium(III) complexes by periodate is proposed, and this is supported by an excellent isokinetic relationship between ΔH* and ΔS* values for these reactions.