Intramolecular Optical Electron Transfer in Mixed-Valent Dinuclear Iron−Ruthenium Complexes Featuring a 1,4-Diethynylaryl Spacer

The ground-state electronic structure and the lowest-lying excited states of the cationic mixed-valent dinuclear complexes [(η²-dppe)(η⁵-C₅Me₅)Fe[CC-1,4-(C₆H₄)CC]Ru(η²-dppe)₂(X)][PF₆] (X = Cl, 2; X = CC(4-C₆H₄NO₂), 5) are discussed, with particular emphasis on the photoinduced intramolecular electron transfer between the ruthenium and iron centers. The location and intensities of the low-lying absorptions exhibited in the near-infrared (near-IR) range by these heterodinuclear mixed-valent (MV) complexes correlate with predictions based on the Hush model, strongly suggesting that they correspond to intervalence charge-transfer (IVCT) bands.