Substituent Effects in the Iron 2p and Carbon 1s Edge Near-Edge X-ray Absorption Fine Structure (NEXAFS) Spectroscopy of Ferrocene Compounds

Abstract

The iron 2p and carbon 1s near-edge X-ray absorption fine structure (NEXAFS) spectra of substituted ferrocene compounds (Fe(Cp-(CH3)5)2, Fe(Cp)(Cp-COOH), Fe(Cp-COOH)2, and Fe(Cp-COCH3)2) are reported and are interpreted with the aid of extended Hückel molecular orbital (EHMO) theory and density functional theory (DFT). Significant substituent effects are observed in both the Fe 2p and C 1s NEXAFS spectra. These effects can be related to the electron donating/withdrawing properties of the cyclopentadienyl ligands and their substituents as well as the presence of pi* conjugation between the cyclopentadienyl ligand and unsaturated substituents.

From co-crystals to functional thin films: photolithography using [2+2] photodimerization

“…STXM images of the unreacted and reacted lms revealed morphologies similar to those imaged using AFM (ESI, Fig. 21,22 A comparison of the C K-edge spectra of the reacted and unreacted lms revealed a relative decrease in the C]C bond of 4,4 0 -bpe (284.6 eV) upon exposure to UV light, which is consistent with cyclobutane formation (Fig. Two signatures for unreacted C]C bonds were present in the C K-edge NEXAFS spectra at 284.6 and 285.8 eV, with the former being assigned to 1s / p* transitions for the olenic C]C bond.…”

Probing the Electronic Structure of Substituted Ferrocenes with High‐Resolution XANES Spectroscopy

“…So far, the lifetime broadening of conventional K‐edge XAS experiments limits their applicability for probing the LUMO states. On the other hand, in L‐edge XAS3 a more intense 2p→nd transition can be used,4 but because of the use of low‐energy radiation, in situ studies of catalytic reactions are not possible with this technique. Therefore, a hard X‐ray technique with a better resolution of the final d‐states than in conventional XAS is required to probe the electronic structure of catalysts in situ.…”

“…The influence of substituting groups at the Cp ring on the electronic structure has been studied both experimentally and theoretically 13. However these experimental studies are limited to soft X‐ray absorption spectroscopy,4, 14 which cannot be used for in situ studies due to the low radiation energy, and photoelectron spectroscopy13c or X‐ray emission experiments8e that only provide information about occupied orbitals. Here, we demonstrate how the complementary information on unoccupied orbitals can be probed with hard X‐ray.…”

Molecular and structural investigation of yukonite (synthetic & natural) and its relation to arseniosiderite

“…In both cases a coarse step size of 0.5 eV was taken before the first edge and a fine step of 0.04 eV at the main absorption edges. The energy scale for the Fe 2p XANES measurements was calibrated to the highest intensity L 3 peak of hematite (a-Fe 2 O 3 ) occurring at 709.50 ± 0.01 eV (Garvie et al, 1994;van Aken et al, 1998;van Aken and Liebscher, 2002;van Aken and Lauterbach, 2003;Otero et al, 2008). The energy scale of the Ca 2p XANES spectra was not calibrated against an absolute standard as in other works (Naftel et al, 2001;Fleet and Liu, 2009).…”

“…The Fe 3+ state in yukonite (natural and synthetic) was deduced to be in a paramagnetic high spin state (ground: $ 6 A 1g + 2 T 2g ) since no feature (at $705 eV) characteristic of octahedral low spin Fe 3+ compounds such as K 3 [Fe III (CN) 6 ] was observed (Otero et al, 2008). Therefore, the ferric iron in yukonite (and arseniosiderite) is expected to have an octahedral-type of environment with a possible (t 2g ) 3 (e g ) 2 electronic configuration and an $ 6 S 5/2 electronic ground state configuration (de Groot et al, 1990;de Groot, 2005); and to exhibit a paramagnetic high spin anti-ferromagnetic character as observed in the case of hematite (Fe 2 O 3 ) (van Aken and Lauterbach, 2003), scorodite (FeAsO 4 Á2H 2 O) (Hawthorne, 1976;Jakeman et al, 1991) and FAsH (FeAsO 4 Á0.75H 2 O) (Jakeman et al, 1991).…”