An Unusually Delocalized Mixed‐Valence State of a Cyanidometal‐Bridged Compound Induced by Thermal Electron Transfer

The heterometallic complexes trans‐[Cp(dppe)FeNCRu(o‐bpy)CNFe(dppe)Cp][PF6]n (1[PF6]n, n=2, 3, 4; o‐bpy=1,2‐bis(2,2′‐bipyridyl‐6‐yl)ethane, dppe=1,2‐bis(diphenylphosphino)ethane, Cp=1,3‐cyclopentadiene) in three distinct states have been synthesized and fully characterized. 13+[PF6]3 and 14+[PF6]4 are the one‐ and two‐electron oxidation products of 12+[PF6]2, respectively. The investigated results suggest that 1[PF6]3 is a Class II mixed valence compound. 1[PF6]4 after a thermal treatment at 400 K shows an unusually delocalized mixed valence state of [FeIII‐NC‐RuIII‐CN‐FeII], which is induced by electron transfer from the central RuII to the terminal FeIII in 1[PF6]4, which was confirmed by IR spectroscopy, magnetic data, and EPR and Mössbauer spectroscopy. Heat to delocalize: Thermal activation at 400 K causes a localized diamagnetic cyanidometal‐bridged polynuclear compound [FeIII‐NC‐RuII‐CN‐FeIII] to transform into an unusually delocalized mixed‐valence state [FeIII‐NC‐RuIII‐CN‐FeII].