The Bonding Situation in the Dinuclear Tetra-Hydrido Complex [{⁵CpFe}₂(μ-H)₄] Revisited by Hard X-Ray Spectroscopy

High energy resolution fluorescence detected XANES (HERFD-XANES) and valence-to-core X-ray emission spectroscopy (VtC-XES) are introduced as powerful tools to investigate hydride-iron interaction, the possible iron-iron bond, and iron spin state of the dinuclear tetra-hydrido complex [{⁵CpFe}₂(μ-H)₄] (1H, ⁵Cp = η⁵-C₅ iPr₅) by thoroughly accessing the geometric and electronic structure of this complex in comparison to the nonhydride reference [⁵CpCpFe] (1, Cp = C₅H₅). The so far observed most intense hydride induced signals in the pre-edge feature of the HERFD-XANES and in the VtC-XES spectra at the iron K-edge allow a precise analysis of the LUMO and HOMO states, respectively, by application of time-dependent density function theory (TD-DFT) and density functional theory (DFT) calculations. The results of these calculations are further employed to understand the oxidation state, spin states, and potential Fe-Fe bonds in this complex.