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Kinetics and mechanism of the one‐step, two‐electron oxidation of diaquadichloro(1,10‐phenanthroline)chromium(III) chloride dihydrate by periodate to chromium(V) in aqueous acidic solutions
Author(s) -
Eltahir Sawsan B.,
Ali Ismat H.,
Sulfab Yousif
Publication year - 2021
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.21527
Subject(s) - chemistry , chromium , periodate , reaction rate constant , aqueous solution , kinetics , phenanthroline , ligand (biochemistry) , chloride , electron transfer , inorganic chemistry , reaction mechanism , medicinal chemistry , stereochemistry , organic chemistry , catalysis , biochemistry , physics , receptor , quantum mechanics
The kinetics of oxidation of [Cr III Cl 2 (phen)(H 2 O) 2 ]Cl⋅2H 2 O (phen = 1,10‐phenanthroline) by periodate {I(VII)} have been studied in aqueous acidic solutions. The oxidation product has been isolated and characterized by elemental analysis, IR, and ESR as [Cr V Cl 2 (phen)(O)]Cl⋅1.5H 2 O. Under pseudo–first‐order conditions, the reaction showed first‐order dependence on the initial Cr(III) complex concentration. At fixed reaction conditions, the dependence of k obs on [I(VII)] showed saturation kinetics. The rate constant, k obs , increased with increasing pH, indicating that the hydroxo form of the chromium(III) complex is the most reactive species. A plot of k obs ([H + ] + K 1 ) versus [H + ] is linear with an intercept, indicating that the reaction proceeds via two parallel pathways. One pathway is independent of [H + ] and the other on [H + ] –1 . Since water is known to be a very weak bridging ligand, the pathway involving the aqua form of the complex, almost certainly, is bridged to periodate via the chloro ligand of the chromium(III) complex. The thermodynamic parameters of the processes involved are reported. A one‐step two‐electron transfer via an inner‐sphere mechanism has been assigned to the two pathways based on the form of the rate law