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

Abstract

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.

Pentaisopropyl Cyclopentadienyl: An Overview across the Periodic Table

“… Different reactions of pentaisopropylcyclopentadienide iron bromide dme‐adduct, 20 c , as reported by Sitzmann et al. in 2011, [39] 2017 [44] and 2019 [38] …”

“…This complex was investigated with Valence‐to‐core X‐ray emission spectroscopy (vtc‐XES) and high‐energy‐resolution fluorescence detected X‐ray absorption near edge structure (HERFD‐XANES) in combination with DFT calculations. This provided information on the bonding situation and oxidation state of the iron centers, suggesting that both iron centers are in the low‐spin state in the oxidation state +II and there is no Fe−Fe bonding interaction [38] . Reaction of half‐sandwich iron bromide 20 c with 2,6‐diisopropylphenylmagnesium bromide Grignard‐reagent gives the diorgano iron complex 5 CpFeDip (Dip=2,6‐diisopropylphenyl), 20 e .…”

Planar Iron Hydride Nanoclusters: Combined Spectroscopic and Theoretical Insights into Structures and Building Principles

“…[4,5] The VtC signal is especially sensitive towards metalÀ hydride interactions. [23,24] Direct comparison of the experimental VtC spectrum of 1 and theoretical spectra derived from DFT calculations proved the presence of iron hydride motifs (Figure 4D). The major signal at 7107 eV and the shoulder at 7110 eV showed high reproducibility only with a μ 2 -dihydrido Fe 4 structure.…”

“…The bridging hydrides in complex 1 were observed by crystal structure analysis and IR spectroscopy [4,5] . The VtC signal is especially sensitive towards metal−hydride interactions [23,24] . Direct comparison of the experimental VtC spectrum of 1 and theoretical spectra derived from DFT calculations proved the presence of iron hydride motifs (Figure 4D).…”

“…These results are in full agreement with earlier studies of the tetrahydride complex [{CpFe} 2 (μ-H) 4 ] which involved a similar 7107 eV emission of the HÀ Fe motifs. [24]…”