Designing Molecules for Metal−Metal Electronic Communication: Synthesis and Molecular Structure of the Couple of Heterobimetallic Isomers [η6-(2-Ferrocenyl)indene]-Cr(CO)3 and [η6-(3-Ferrocenyl)indene]-Cr(CO)3
摘要:
The heterobinuclear isomers [eta(6)-(2-ferrocenybindene]-Cr(CO)(3) (1) and [eta(6)-(3-/errocenyl)indene]-Cr(CO)(3) (2) have been prepared and the crystal structure determination showed that the Fe(C5H5) and Cr(CO)(3) groups in the two molecules are disposed in different conformations with respect to the Cp-indene bridging ligand, cisoid in 1 and transoid in 2. Preliminary electrochemical (CV) and spectroscopic (IR and near-IR) results obtained for the corresponding monooxidized 1(+) and 2(+) demonstrate the existence of stronger electronic coupling in 1(+) than in 2(+).
A series of ferrocenyl-based complexes of general structure [eta(5)-(2-ferrocenyl)indenyI]MLn [MLn = 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 MLn 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.
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.