Theoretical Analysis of Fe K‐edge XANES on Mononitrosyl Iron Complex [(NO)Fe(S2C6H4)2][PPN]

In this study, a detailed calibration of the performance of modern ab initio wave function methods in the domain of X-ray absorption spectroscopy (XAS) is presented. It has been known for some time that for a given level of approximation, for example, using time-dependent density functional theory (TD-DFT) in conjunction with a given basis set, there are systematic deviations of the calculated transition energies from their experimental values that depend on the functional, the basis set, and the chosen treatment of scalar relativistic effects. This necessitates a linear correlation for a given element/functional/basis set combination to be established before chemical applications can be performed. This is a laborious undertaking since it involves sourcing trustworthy experimental data, lengthy geometry optimizations, and detailed comparisons between theory and experiment. In this work, reference values for the element-specific shifts of all the first-row transition metal atoms and the main group elements C, N, O, F, Si, P, S, and Cl have been computed by using a protocol that is based on the complete active space configuration interaction in conjunction with second-order N-electron valence state perturbation theory (CASCI/NEVPT2). It is shown that by extrapolating the results to the basis set limit of the method and taking into account scalar relativistic effects via the second-order Douglas-Kroll-Hess (DKH2) corrections, the predicted element shifts are on average less than 0.75 eV across all the absorption edges and a very good agreement between theory and experiment in all the studied XAS cases is observed. The transferability of these errors to molecular systems is thoroughly investigated. The constructed CASCI/NEVPT2 database of element shifts is used to evaluate the performance and to automatically calibrate prior to comparison with the experiment two commonly used methods in X-ray spectroscopy, namely, DFT/Restricted open shell configuration interaction singles (DFT/ROCIS) and TD-DFT methods.

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Ab Initio Wave Function-Based Determination of Element Specific Shifts for the Efficient Calculation of X-ray Absorption Spectra of Main Group Elements and First Row Transition Metals

Chantzis

Kowalska

Maganas

et al. 2018

J. Chem. Theory Comput.

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Theoretical Analysis of Fe K-Edge XANES on Iron Pentacarbonyl

et al. 2020

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Iron pentacarbonyl (Fe(CO) 5 ) is a versatile material that is utilized as an inhibitor of flame, shows soot suppressibility, and is used as a precursor for focused electron-beam-induced deposition (FEBID). X-ray absorption near-edge structure (XANES) of the K edge, which is a powerful technique for monitoring the oxidation states and coordination environment of metal sites, can be used to gain insight into Fe(CO) 5 -related reaction mechanisms in in situ experiments. We use a finite difference method (FDM) and molecular-orbital-based time-dependent density functional theory (TDDFT) calculations to clarify the Fe K-edge XANES features of Fe(CO) 5 . The two pre-edge peaks P 1 and P 2 are mainly the Fe(1s) → Fe−C(σ*) and Fe(1s) → Fe−C(π*) transitions, respectively. When the geometry transformed from D 3h to C 4v symmetry, a ∼30% decrease of the pre-edge P 2 intensity was observed in the simulated spectra. This implies that the π bonding of Fe and CO is sensitive to changes in geometry. The following rising edge and white line regions are assigned to the Fe(1s) → Fe(4p)(mixing C(2p)) transitions. Our results may provide useful information to interpret XANES spectra variations of in situ reactions of metal−CO or similar compounds with π acceptor ligandlike metal−CN complexes.

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Insight into the Reactivity and Electronic Structure of Dinuclear Dinitrosyl Iron Complexes

Hsu

et al. 2014

Inorg. Chem.

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A combination of N/S/Fe K-edge X-ray absorption spectroscopy (XAS), X-ray diffraction data, and density functional theory (DFT) calculations provides an efficient way to unambiguously delineate the electronic structures and bonding characters of Fe-S, N-O, and Fe-N bonds among the direduced-form Roussin's red ester (RRE) [Fe2(μ-SPh)2(NO)4](2-)(1) with {Fe(NO)2}(10)-{Fe(NO)2}(10) core, the reduced-form RRE [Fe2(μ-SPh)2(NO)4](-)(3) with {Fe(NO)2}(9)-{Fe(NO)2}(10) core, and RRE [Fe2(μ-SPh)2(NO)4] (4) with {Fe(NO)2}(9)-{Fe(NO)2}(9) core. The major contributions of highest occupied molecular orbital (HOMO) 113α/β in complex 1 is related to the antibonding character between Fe(d) and Fe(d), Fe(d), and S atoms, and bonding character between Fe(d) and NO(π*). The effective nuclear charge (Zeff) of Fe site can be increased by removing electrons from HOMO to shorten the distances of Fe···Fe and Fe-S from 1 to 3 to 4 or, in contrast, to increase the Fe-N bond lengths from 1 to 3 to 4. The higher IR νNO stretching frequencies (1761, 1720 cm(-1) (4), 1680, 1665 cm(-1) (3), and 1646, 1611, 1603 cm(-1) (1)) associated with the higher transition energy of N1s →σ*(NO) (412.6 eV (4), 412.3 eV (3), and 412.2 eV (1)) and the higher Zeff of Fe derived from the transition energy of Fe1s → Fe3d (7113.8 eV (4), 7113.5 eV (3), and 7113.3 eV (1)) indicate that the N-O bond distances of these complexes are in the order of 1 > 3 > 4. The N/S/Fe K-edge XAS spectra as well as DFT computations reveal the reduction of complex 4 yielding complex 3 occurs at Fe, S, and NO; in contrast, reduction mainly occurs at Fe site from complex 3 to complex 1.

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Theoretical Analysis of Fe K‐edge XANES on Mononitrosyl Iron Complex [(NO)Fe(S₂C₆H₄)₂][PPN]

Cited by 5 publications

References 62 publications

Ab Initio Wave Function-Based Determination of Element Specific Shifts for the Efficient Calculation of X-ray Absorption Spectra of Main Group Elements and First Row Transition Metals

Ab Initio Wave Function-Based Determination of Element Specific Shifts for the Efficient Calculation of X-ray Absorption Spectra of Main Group Elements and First Row Transition Metals

Theoretical Analysis of Fe K-Edge XANES on Iron Pentacarbonyl

Insight into the Reactivity and Electronic Structure of Dinuclear Dinitrosyl Iron Complexes

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