A Mixed-Valence Octanuclear Iron−Oxo Pyrazolate: Assessment of Electronic Delocalization by Structural and Spectroscopic Analysis

A formally FeIII7FeII complex, containing an inner Fe4O4-cubane and four peripheral Fe centers, is derived from the one-electron reduction of its FeIII8 precursor. Spectroscopic analysis of the former reveals that the redox activity of this Fe8 system is confined within its cubane core. The resulting (Fe4O4)3+-cubane, which is valence-delocalized in the NMR, Mössbauer, and IR spectroscopy time scales but valence-trapped in the X-ray photoelectron spectroscopy (XPS) time scale, is better described as a Robin−Day class-II system by the analysis of its near-infrared (NIR) intervalence charge transfer (IVCT) band profile.