Electron transfer at the class II/III borderline of mixed valency: Dependence of rates on solvent dynamics and observation of a localized-to-delocalized transition in freezing solvents

Starla D. Glover, Benjamin J. Lear, J. Catherine Salsman, Casey H. Londergan, Clifford P. Kubiak

Research output: Contribution to journalArticlepeer-review

23 Scopus citations

Abstract

The dependence of the rates of intramolecular electron transfer (ET) of mixed-valence complexes of the type {[Ru3O(OAc)6(CO)(L)]2-BL}−1, where L is the pyridyl ligand and BL is the pyrazine on solvent type and temperature is described. Complexes were reduced chemically to obtain the mixed-valence anions in acetonitrile (CH3CN) and methylene chloride (CH2Cl2). Rate constants for intramolecular ET were estimated by simulating the observed degree of ν(CO) infrared (IR) bandshape coalescence in the mixed-valence state. In the strongly coupled mixed-valence states of these complexes, the electronic coupling, HAB, approaches λ/2, where λ is the total reorganization energy. The activation energy is thus nearly zero, and rate constants are in the ‘ultrafast’ regime where they depend on the pre-exponential terms within the frequency factor, νN. The frequency factor contains both external (solvent dynamics) and internal (molecular vibrations) contributions. In general, external solvent motions are slower than internal vibrations, and therefore control ET rates in fluid solution. A profound increase in the degree of ν(CO) IR bandshape coalescence is observed as the temperature approaches the freezing points of the solvents methylene chloride (f.p. −92°C) and acetonitrile (f.p. −44°C). Decoupling the slower solvent motions involved in the frequency factor νN for ET by freezing the solvent causes a transition from solvent dynamics to internal vibration-limited rates. The solvent phase transition causes a localized-to-delocalized transition in the mixed-valence ions that accelerates the rate of ET.

Original languageEnglish (US)
Pages (from-to)177-185
Number of pages9
JournalPhilosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
Volume366
Issue number1862
DOIs
StatePublished - Jan 13 2008

All Science Journal Classification (ASJC) codes

  • Mathematics(all)
  • Engineering(all)
  • Physics and Astronomy(all)

Fingerprint Dive into the research topics of 'Electron transfer at the class II/III borderline of mixed valency: Dependence of rates on solvent dynamics and observation of a localized-to-delocalized transition in freezing solvents'. Together they form a unique fingerprint.

Cite this