Electrostatic bending and outer-sphere intervalence transfer in a flexible ligand-bridged ruthenium(III)-iron(II) complex
In the mixed-valence complex [RuIII(NH3)5(μ-dpypn)FeII(CN)5] with the flexible bridging ligand 1,3-di(4-pyridyl)propane (dpypn), electrostatic interactions between the {Ru(NH3)5}3+ and {Fe(CN)5}3− moieties drive a strong bending of dpypn and approximation of the RuIII and FeII centers, from which the enhanced electronic coupling between metal ions produces an intense intervalence-transfer absorption in the near-infrared region. Density functional theory calculations corroborate both the electrostatic bending in this heterobinuclear complex and a linear geometry in the homobinuclear counterparts [Ru(NH3)5(μ-dpypn)Ru(NH3)5]5+ and [Fe(CN)5(μ-dpypn)Fe(CN)5]5−, for which no evidence of electronic coupling was found because of the separation between metal centers. Furthermore, the heterobinuclear species formed an inclusion complex with β-cyclodextrin where the imposed linear geometry prevents significant electronic coupling and intervalence charge transfer between the RuIII and FeII centers.
