NDLI: One- and two-electron reduction of chromium(VI) by polyaminocarboxylatocobaltate(II) complexes and the formation of chromium(V) and chromium(IV)

Content Provider	Springer Nature Link
Author	Salih, Isam M. A. Sulfab, Yousif
Copyright Year	2016
Abstract	The kinetics of the oxidation of Co$^{II}$L$^{n}$ complexes {where L = ethylenediaminetetraacetate (EDTA), diethylenetriaminepentaacetate (DTPA), or N-(2-hydroxyethyl)ethylenediaminetriacetate (HEDTA)} by Cr$^{VI}$ were studied under pseudo-first-order conditions with [Co$^{II}$L$^{n}$] ≫ [Cr$^{VI}$]. The kinetics showed first-order dependence on [Cr$^{VI}$]. The rate constant, k $_{obs}$, decreases with increasing concentration of [Cr$^{VI}$]. At constant [H$^{+}$], ionic strength, and temperature, the rate law is described by Eq. (i) i $$ - {\text{d}}\left[ {{\text{Cr}}^{\text{VI}} } \right] / {\text{dt}} = \left\{ {{\text{k}}_{ 2} \left[ {{\text{Co}}^{\text{II}} {\text{L}}^{\text{n}} } \right]{\text{ + k}}_{ 3} \left[ {{\text{Co}}^{\text{II}} {\text{L}}^{\text{n}} } \right]^{ 2} } \right\}\left[ {{\text{HCrO}}_{4}^{ - } } \right] $$ Both k $_{2}$ and k $_{3}$ showed acid-dependent and acid-independent pathways. The direct conversion Co$^{II}$L$^{n}$ to Co$^{III}$L$^{m}$ is ruled out by spectrophotometric and ESR spectroscopic measurements that showed the formation of initial reaction intermediate(s). The rate law is consistent with one-electron and concurrent two-electron transfers leading to the formation of Cr$^{V}$ and Cr$^{IV}$, respectively. An inner-sphere process, at least for the first term, leading to the formation of a relatively stable Cr$^{V}$ species is almost certain. The kinetic term showing second-order dependence on [Co$^{II}$L$^{n}$], most likely, involves concurrent two-electron transfer leading to the formation of Cr$^{IV}$. The type of rate law and the proposed mechanism, reported here, depart from the well-established rate laws observed and mechanisms proposed for the oxidation of one-electron reductants by Cr$^{VI}$.
Starting Page	315
Ending Page	323
Page Count	9
File Format	PDF
ISSN	03404285
Journal	Transition Metal Chemistry
Volume Number	41
Issue Number	3
e-ISSN	1572901X
Language	English
Publisher	Springer International Publishing
Publisher Date	2016-02-01
Publisher Place	Cham
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Catalysis Physical Chemistry Inorganic Chemistry
Content Type	Text
Resource Type	Article
Subject	Materials Chemistry Metals and Alloys Inorganic Chemistry

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