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 [(η<sup>2</sup>-dppe)(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)Fe[CC-1,4-(C<sub>6</sub>H<sub>4</sub>)CC]Ru(η<sup>2</sup>-dppe)<sub>2</sub>(X)][PF<sub>6</sub>] (X = Cl, <b>2</b>; X = CC(4-C<sub>6</sub>H<sub>4</sub>NO<sub>2</sub>), <b>5</b>) 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.