Intervalence Charge Transfer in Cationic Heterotrinuclear Fe(III)-Rh(I)-Cr(0) Triads of the Polyaromatic Cyclopentadienyl-Indenyl Ligand

The challenge to realize polymetallic assemblies of unambiguous structure and stereochemistry, in which the nature of the intervalence transition (IT) is rationalized, has been faced by investigating the syn and anti isomers of eta(6)-Cr(CO)(3){eta(5)-[(2-ferrocenyl)indenyl]Rh(CO)(2)} and their mixed-valence cations. Crystallographic studies and DFT calculations provide a detailed description of the structural and electronic features of these complexes, evidencing a significant difference in geometrical distortions and frontier MO composition between syn and anti isomers. Mixed-valence cations are generated and monitored by low-temperature spectroelectrochemistry in the visible, IR, and near-IR regions. The IT bands in the near-ER spectra are rationalized in the framework of Marcus Hush theory and at quantum chemistry level by density functional theory. Noteworthy, the results reported provide rare experimental evidence that the presence of a third metal center (Rh) increases the metal metal (Fe-Cr) interaction with respect to the structurally correlated binuclear system.