Open AccessLow Reorganization Energy for Electron Self-Exchange by a Formally Copper(III,II) Redox Couple
Author(s) -
Timothy J. Zerk,
Caroline T. Saouma,
James M. Mayer,
William B. Tolman
Publication year - 2019
Publication title -
inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.348
H-Index - 233
eISSN - 1520-510X
pISSN - 0020-1669
DOI - 10.1021/acs.inorgchem.9b02185
Subject(s) - chemistry , redox , electron exchange , copper , ionic bonding , titration , reaction rate constant , redox titration , electrochemistry , inorganic chemistry , ion , electrode , kinetics , organic chemistry , physics , quantum mechanics
The rate constant for electron self-exchange ( k 11 ) between LCuOH and [LCuOH] - (L = bis-2,6-(2,6-diisopropylphenyl)carboximidopyridine) was determined using the Marcus cross relation. This work involved measurement of the rate of the cross-reaction between [Bu 4 N][LCuOH] and [Fc][BAr 4 F ] (Fc + = ferrocenium; BAr 4 F = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate)) by stopped-flow methods at -88 °C in CH 2 Cl 2 and measurement of the equilibrium constant for the redox process by UV-vis titrations under the same conditions. A value of k 11 = 3 × 10 4 M -1 s -1 (-88 °C) led to estimation of a value 9 × 10 6 M -1 s -1 at 25 °C, which is among the highest values known for copper redox couples. Further Marcus analysis enabled determination of a low reorganization energy, λ = 0.95 ± 0.17 eV, attributed to minimal structural variation between the redox partners. In addition, the reaction entropy (Δ S °) associated with the LCuOH/[LCuOH] - self-exchange was determined from the temperature dependence of the redox potentials, and found to be dependent upon ionic strength. Comparisons to other Cu redox systems and potential new applications for the formally Cu III,II system are discussed.