Beschreibung:
<jats:title>Abstract</jats:title><jats:p>Broadening and coalescence of infrared bands can occur due to chemical exchange processes occurring on very fast, femtosecond‐to‐picosecond timescales. One such fast process of recent investigation is intramolecular electron transfer in transition‐metal complexes with strong communication between electron‐donor and ‐acceptor sites. The observation of partial coalescence of metal–carbonyl stretching bands in hexanuclear ruthenium mixed‐valence complexes due to electron‐transfer rates on the order of 10<jats:sup>11</jats:sup>–10<jats:sup>12</jats:sup> s<jats:sup>−1</jats:sup> is chronicled here. Several important advances have been made with the aid of dynamic infrared‐band coalescence in these complexes, including the observation of dynamic solvent relaxation effects on electron‐transfer rates, the determination of the equilibrium constant between charge‐transfer isomers, and a reconsideration of the theory of electron transfer and delocalization in bridged, near‐delocalized electron‐transfer systems.</jats:p>