Mixed Valence Properties in Ferrocenyl-Based Bimetallic FeCp−Indenyl-MLn Complexes: Effect of the MLn Group

A series of ferrocenyl-based complexes of general structure [eta(5)-(2-ferrocenyl)indenyI]ML(n) [ML(n) = RuCp*, FeCp, IrCOD, Mn(CO)(3), and Cr(CO)(2)NO] were synthesized with the aim of tuning the effect of the nature of the second metal group ML(n) on the magnitude of the metal-metal electronic coupling in their mixed valence ions generated by electrochemical oxidation. The electronic interaction was probed by determining different and independent physical properties, the potential splitting in the cyclic voltammograms, and the IT bands in the near-IR spectra, which were rationalized in the framework of Marcus-Hush theory and at the quantum chemistry level by the density functional theory and TD density functional theory methods. On the basis of the obtained results, we were able to establish a trend based on the magnitude of the Fe-M electron transfer parameters H(ab) and alpha ranging from weakly to moderately coupled mixed valence ions.