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Thermodynamics of Redox Processes and Kinetics and Mechanism of Electron Self‐Exchange Reactions in the Bis( N , N ‐diethyldithiocarbamato)copper( II )/Iodine/Dichloromethane System
Author(s) -
Shtyrlin Valery G.,
Zakharov Alexey V.,
Kuznetsov Andrey M.,
Kukushkina Ol’ga V.,
Chernov Pavel P.
Publication year - 2002
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/1099-0682(200211)2002:11<2947::aid-ejic2947>3.0.co;2-w
Subject(s) - chemistry , copper , reaction rate constant , redox , dichloromethane , electron transfer , kinetics , electron exchange , reaction mechanism , delocalized electron , inorganic chemistry , computational chemistry , solvent , catalysis , ion , organic chemistry , physics , quantum mechanics
The thermodynamics of complex formation between Et 4 NI and I 2 in CH 2 Cl 2 and the redox processes in the bis( N , N ‐diethyldithiocarbamato)copper( II ) [Cu II L 2 ]/I 2 /CH 2 Cl 2 system have been studied spectrophotometrically. The reversibility of the reactions of formation of copper( III ) complexes was established and their thermodynamic parameters determined: Cu II L 2 + 3 / 2 I 2 ⇄ [Cu III L 2 ]I 3 {log K = 5.80 (298 K), Δ H = −35.0 kJ·mol −1 , and Δ S = −6.7 J·K −1 ·mol −1 } and [Cu III L 2 ]I 3 + I 2 ⇄ [Cu III L 2 ]I 5 {log K = 2.02 (298 K), Δ H = −11.1 kJ·mol −1 , and Δ S = 1.3 J·K −1 ·mol −1 }. The rate constants and activation parameters for the electron self‐exchange reactions between Cu II L 2 and [Cu III L 2 ]I n ( n = 3, 5) in the CD 2 Cl 2 solutions were determined by NMR line‐broadening of the ligand L protons: k e = 3.0·10 8 M −1 ·s −1 (298 K), Δ H ≠ = 6.1 kJ·mol −1 , and Δ S ≠ = −62.3 J·K −1 mol −1 . To account for the kinetic parameters, an unusual mechanism for the self‐exchange reaction was suggested. This mechanism involves the prior formation of the Cu II L 2 I n Cu III L 2 intermediate, in which considerable delocalization of electron density through the orbitals of copper and bridging iodine atoms is achieved, followed by electron transfer. The formation of the intermediate was supported by ESR data and quantitative analysis of the activation parameters with the use of quantum chemical computations by the DFT method at the B3LYP/3‐21G* level. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)