After nearly 50 years of study, answering the question of whether an inorganic mixed valence system is fully delocalized (Robin � Day Class III) or not remains a challenge.  We employ coalescence of ?(CO) bandshapes in 1D infrared (IR) spectra  of mixed valence complexes to determine rate constants of electron transfer (ET).  These studies have revealed some unusual behaviors such as rates of ET that get faster as the temperature is decreased, and failure to conform to several of the major tenets of the Marcus-Hush theory of electron transfer.  Most of these apparent anomalies are resolved by the following physical picture.  (1) Rate constants are in the �ultrafast� regime where they depend on the pre-exponential terms within the frequency factor, ?N; (2) The frequency factor contains both external (solvent dynamics) and internal (molecular vibrations) contributions, and solvent motions are generally slower than internal vibrations; (3)  Decoupling the slower solvent motions involved in the frequency factor ?N for ET by freezing the solvent causes a transition from solvent dynamics to internal vibration limited rates.  (4) A three state model of mixed valency that predicts two intervalence charge transfer (IVCT) bands and their response to increasing degrees of electronic communication, solvent, and temperature applies.  These studies of systems progressing through a localized-to-delocalized transition have provided general guidelines for establishing where a particular mixed valence system lies along the borderline. Two key points learned from the investigation of these mixed valence systems are: solvent dynamics tend to localize otherwise delocalized states, and delocalization on the timescale of the fastest (inertial) solvent motions is not sufficient to achieve complete electronic delocalization.  Extending ideas we have learned from ultrafast mixed valency, we can begin to describe electron transfer reactions in high order supramolecular triruthenium cluster assemblies, hydrogen bonded systems, and across metallic and semiconducting nanoparticles.

Award Address  (ACS Award in Inorganic Chemistry sponsored by Aldrich Chemical Co., Inc,). Inorganic electron transfer: Sharpening a fuzzy border in mixed valency and extending mixed valency across supramolecular systems and nanoparticles

243rd National Meeting (2012)

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