uu.seUppsala University Publications
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Electronic structure investigations of transition metal complexes through X-ray spectroscopy
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry.
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Description
Abstract [en]

Catalysts based on the first-row (3d) transition metals are commonly seen in chemical and biological reactions. To understand the role of the transition metal in the catalyst, the element specific technique core level spectroscopy is used to probe the electronic structure and geometric properties centered around the metal site. Different types of X-ray spectra can be applied to probe the metal 3d character orbitals involved in reactions, which make it possible to identify and characterize the reactive sites of samples in different forms. A detailed interpretation and understanding of the different X-ray spectra requires a unified method which can be used to model different types of X-ray spectra, e.g., soft and hard X-rays. In this thesis, theoretical investigations of the electronic structures of 3d transition metal complexes through X-ray spectroscopy are presented. The restricted active space method (RAS) is used to successfully reproduce different types of X-ray spectra by including all important spectral effects: multiplet structures, spin-orbit coupling, charge-transfer excitations, ligand field splitting and 3d-4p orbital hybridization. Different prototypes of molecules are adopted to test the applicability of the RAS theory.

The metal L edge X-ray absorption (XAS) spectra of low spin complexes [Fe(CN)6]n and [Fe(P)(ImH)2]n in ferrous and ferric oxidation state are discussed. The RAS calculations on iron L edge spectra of these comparing complexes have been performed to fingerprint the oxidation states of metal ion, and different ligand environments. The Fe(P) system has several low-lying spin states in the ground state, which is used as a model to identify unknown species by their spectroscopic fingerprints through RAS spectra simulations. To pave the route of understanding the electronic structure of oxygen evolution complex of Mn4CaO5 cluster, the MnII(acac)2 and MnIII(acac)3 are adopted as prototypical Mn-complexes. The 3d partial fluorescence yield-XAS are employed on the Mn L-edge in solution. Combining experiments and RAS calculations, primary questions related to the oxidation state and spin state are discussed.

The first application to simulate the metal K pre-edge XAS of mono-iron complexes and iron dimer using RAS method beyond the electric dipole is completed by implementing the approximate origin independent calculations for the intensities. The K pre-edge spectrum of centrosymmetric complex [FeCl6]n– ferrous state is discussed as s and a donor model systems. The intensity of the K pre-edge increases significantly if the centrosymmetric environment is broken, e:g:, when going from a six-coordinate to the four-coordinate site in [FeCl4]n. Distortions from centrosymmetry allow for 3d-4p orbital hybridization, which gives rise to electric dipole-allowed transitions in the K pre-edge region. In order to deliver ample electronic structure details with high resolution in the hard X-ray energy range, the two-photon 1s2p resonant inelastic X-ray scattering process is employed. Upon the above successful applications of one-photon iron L edge and K pre-edge spectra, the RAS method is extended to simulate and interpret the 1s2p resonant inelastic X-ray scattering spectra of [Fe(CN)6]n in ferrous and ferric oxidation states. The RAS applications on X-ray simulations are not restricted to the presented spectra in the thesis, it can be applied to the photon process of interest by including the corresponding core and valence orbitals of the sample.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. , 73 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1541
Keyword [en]
transition metal complexes, x-ray spectroscopy, electronic structures
National Category
Theoretical Chemistry Physical Chemistry
Research subject
Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-328072ISBN: 978-91-513-0035-1 (print)OAI: oai:DiVA.org:uu-328072DiVA: diva2:1133777
Public defence
2017-10-06, Polhemssalen, Ång/10134, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:30 (English)
Opponent
Supervisors
Available from: 2017-09-14 Created: 2017-08-16 Last updated: 2017-09-14
List of papers
1. Restricted active space calculations of L-edge X-ray absorption spectra: From molecular orbitals to multiplet states
Open this publication in new window or tab >>Restricted active space calculations of L-edge X-ray absorption spectra: From molecular orbitals to multiplet states
Show others...
2014 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 141, no 12, 124116Article in journal (Refereed) Published
Abstract [en]

The metal L-edge (2p -> 3d) X-ray absorption spectra are affected by a number of different interactions: electron-electron repulsion, spin-orbit coupling, and charge transfer between metal and ligands, which makes the simulation of spectra challenging. The core restricted active space (RAS) method is an accurate and flexible approach that can be used to calculate X-ray spectra of a wide range of medium-sized systems without any symmetry constraints. Here, the applicability of the method is tested in detail by simulating three ferric (3d(5)) model systems with well-known electronic structure, viz., atomic Fe3+, high-spin [FeCl6](3-) with ligand donor bonding, and low-spin [Fe(CN)(6)](3-) that also has metal backbonding. For these systems, the performance of the core RAS method, which does not require any system-dependent parameters, is comparable to that of the commonly used semi-empirical charge-transfer multiplet model. It handles orbitally degenerate ground states, accurately describes metal-ligand interactions, and includes both single and multiple excitations. The results are sensitive to the choice of orbitals in the active space and this sensitivity can be used to assign spectral features. A method has also been developed to analyze the calculated X-ray spectra using a chemically intuitive molecular orbital picture.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-236075 (URN)10.1063/1.4896373 (DOI)000342844100021 ()25273421 (PubMedID)
Note

Correction in: Journal of Chemical Physics, vol. 141, issue 4, article number: 149905, DOI: 10.1063/1.4908043 ISI: 000349847000064

Available from: 2014-11-12 Created: 2014-11-12 Last updated: 2017-08-16Bibliographically approved
2. Cost and sensitivity of restricted active-space calculations of metal L-edge X-ray absorption spectra
Open this publication in new window or tab >>Cost and sensitivity of restricted active-space calculations of metal L-edge X-ray absorption spectra
Show others...
2016 (English)In: Journal of Computational Chemistry, ISSN 0192-8651, E-ISSN 1096-987X, Vol. 37, no 5, 477-486 p.Article in journal (Refereed) Published
Abstract [en]

The restricted active-space (RAS) approach can accurately simulate metal L-edge X-ray absorption spectra of first-row transition metal complexes without the use of any fitting parameters. These characteristics provide a unique capability to identify unknown chemical species and to analyze their electronic structure. To find the best balance between cost and accuracy, the sensitivity of the simulated spectra with respect to the method variables has been tested for two models, [FeCl6](3-) and [Fe(CN)(6)](3-). For these systems, the reference calculations give deviations, when compared with experiment, of 1 eV in peak positions, 30% for the relative intensity of major peaks, and 50% for minor peaks. When compared with these deviations, the simulated spectra are sensitive to the number of final states, the inclusion of dynamical correlation, and the ionization potential electron affinity shift, in addition to the selection of the active space. The spectra are less sensitive to the quality of the basis set and even a double- basis gives reasonable results. The inclusion of dynamical correlation through second-order perturbation theory can be done efficiently using the state-specific formalism without correlating the core orbitals. Although these observations are not directly transferable to other systems, they can, together with a cost analysis, aid in the design of RAS models and help to extend the use of this powerful approach to a wider range of transition metal systems.

Keyword
transition metals; X-ray absorption spectroscopy; multiconfigurational wavefunction; spin-orbit coupling; charge transfer
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:uu:diva-276263 (URN)10.1002/jcc.24237 (DOI)000369176900002 ()26502979 (PubMedID)
Funder
Swedish National Infrastructure for Computing (SNIC), s00112-267 liu-2012-00060-46Carl Tryggers foundation Marcus and Amalia Wallenberg FoundationSwedish Research Council
Available from: 2016-02-10 Created: 2016-02-10 Last updated: 2017-08-16Bibliographically approved
3. Fingerprinting electronic structures of heme using theoretical modeling of L-edge X-ray absorption spectra
Open this publication in new window or tab >>Fingerprinting electronic structures of heme using theoretical modeling of L-edge X-ray absorption spectra
(English)Manuscript (preprint) (Other academic)
National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-327409 (URN)
Available from: 2017-08-10 Created: 2017-08-10 Last updated: 2017-08-16
4. Probing the oxidation state: A case study of Mn II (acac) 2 and Mn III (acac) 3 on how charge and spin densities determine Mn L-edge X-ray absorption energies
Open this publication in new window or tab >>Probing the oxidation state: A case study of Mn II (acac) 2 and Mn III (acac) 3 on how charge and spin densities determine Mn L-edge X-ray absorption energies
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-327410 (URN)
Available from: 2017-08-10 Created: 2017-08-10 Last updated: 2017-08-16
5. Simulations of iron K pre-edge X-ray absorption spectra using the core restricted active space method
Open this publication in new window or tab >>Simulations of iron K pre-edge X-ray absorption spectra using the core restricted active space method
Show others...
2016 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 4, 3250-3259 p.Article in journal (Refereed) Published
Abstract [en]

The intensities and relative energies of metal K pre-edge features are sensitive to both geometric and electronic structures. With the possibility to collect high-resolution spectral data it is important to find theoretical methods that include all important spectral effects: ligand-field splitting, multiplet structures, 3d-4p orbital hybridization, and charge-transfer excitations. Here the restricted active space (RAS) method is used for the first time to calculate metal K pre-edge spectra of open-shell systems, and its performance is tested against on six iron complexes: [FeCl6](n-), [FeCl4](n-), and [Fe(CN)(6)](n-) in ferrous and ferric oxidation states. The method gives good descriptions of the spectral shapes for all six systems. The mean absolute deviation for the relative energies of different peaks is only 0.1 eV. For the two systems that lack centrosymmetry [FeCl4](2-/1-), the ratios between dipole and quadrupole intensity contributions are reproduced with an error of 10%, which leads to good descriptions of the integrated pre-edge intensities. To gain further chemical insight, the origins of the pre-edge features have been analyzed with a chemically intuitive molecular orbital picture that serves as a bridge between the spectra and the electronic structures. The pre-edges contain information about both ligand-field strengths and orbital covalencies, which can be understood by analyzing the RAS wavefunction. The RAS method can thus be used to predict and rationalize the effects of changes in both the oxidation state and ligand environment in a number of hard X-ray studies of small and medium-sized molecular systems.

National Category
Theoretical Chemistry
Research subject
Chemistry with specialization in Quantum Chemistry
Identifiers
urn:nbn:se:uu:diva-243571 (URN)10.1039/c5cp07487h (DOI)000369506000108 ()26742851 (PubMedID)
Funder
Marcus and Amalia Wallenberg FoundationSwedish Research CouncilCarl Tryggers foundation Knut and Alice Wallenberg Foundation, KAW-2013.0020Swedish National Infrastructure for Computing (SNIC), snic2013-1-317Swedish National Infrastructure for Computing (SNIC), snic2014-5-36
Available from: 2015-02-10 Created: 2015-02-10 Last updated: 2017-08-16Bibliographically approved
6. Applications to metal K pre-edges of transitionmetal dimers illustrate the approximate origin independence for the intensities in the length representation
Open this publication in new window or tab >>Applications to metal K pre-edges of transitionmetal dimers illustrate the approximate origin independence for the intensities in the length representation
2017 (English)In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 115, no 1-2, 174-189 p.Article in journal (Refereed) Published
Abstract [en]

X-ray absorption spectroscopy (XAS) in the metal K pre-edge is a standard probe of electronic and geometric structure of transition metal complexes. Simulating the K pre-edge spectra requires contributions beyond the electric dipole, but if that term is non-zero, the second-order terms, e. g. electric quadrupoles, are no longer origin-independent. In the velocity representation, complete origin independence can be achieved by including all terms to the same order in the oscillator strength. Here, we implement that approach in the length representation and use it for restricted active space (RAS) simulations of metal K pre-edges of iron monomers and dimers. Complete origin independence is not achieved and the size of the remaining errors depends on the electric dipole oscillator strength and its ratio in length and velocity representations. The error in the origin independence is in the ANO basis sets two orders of magnitude smaller than the value of the individual contributions. For systemswith strong electric dipole contributions, the errors are not significant within 3 angstrom from a metal centre, far enough to handlemany multi-metal systems. Furthermore, we discuss the convergence of the multipole expansion, the possibility to assign spectral contributions, and the origin of negative absorption intensities. [GRAPHICS]

Place, publisher, year, edition, pages
TAYLOR & FRANCIS LTD, 2017
Keyword
Multiconfigurational wavefunction, oscillator strengths, quadrupole intensities, properties, X-ray spectroscopy
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-319774 (URN)10.1080/00268976.2016.1225993 (DOI)000396794700015 ()
Funder
Knut and Alice Wallenberg Foundation, KAW-2013.0020Swedish Research Council, 2012-3910 2012-3924
Available from: 2017-04-12 Created: 2017-04-12 Last updated: 2017-08-16Bibliographically approved
7. Molecular orbital simulations of metal 1s2p resonant inelastic X-ray scattering
Open this publication in new window or tab >>Molecular orbital simulations of metal 1s2p resonant inelastic X-ray scattering
Show others...
2016 (English)In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 120, no 29, 5848-5855 p.Article in journal (Refereed) Published
Abstract [en]

For first-row transition metals, high-resolution 3d electronic structure information can be obtained using resonant inelastic X-ray scattering (RIXS). In the hard X-ray region, a K pre-edge (1s -> 3d) excitation can be followed by monitoring the dipole-allowed K alpha (2p -> 1s) or K beta (3p -> 1s) emission, processes labeled 1s2p or 1s3p RIXS. Here the restricted active space (RAS) approach, which is a molecular orbital method, is used for the first time to study hard X-ray RIXS processes. This is achieved by including the two sets of core orbitals in different partitions of the active space. Transition intensities are calculated using both first- and second-order expansions of the wave vector, including, but not limited to, electric dipoles and quadrupoles. The accuracy of the approach is tested for 1s2p RIXS of iron hexacyanides [Fe(CN)(6)](n-) in ferrous and ferric oxidation states. RAS simulations accurately describe the multiplet structures and the role of 2p and 3d spin-orbit coupling on energies and selection rules. Compared to experiment, relative energies of the two [Fe(CN)(6)](3-) resonances deviate by 0.2 eV in both incident energy and energy transfer directions, and multiplet splittings in [Fe(CN)(6)](4-) are reproduced within 0.1 eV. These values are similar to what can be expected for valence excitations. The development opens the modeling of hard X-ray scattering processes for both solution catalysts and enzymatic systems.

National Category
Theoretical Chemistry
Research subject
Chemistry with specialization in Quantum Chemistry
Identifiers
urn:nbn:se:uu:diva-302165 (URN)10.1021/acs.jpca.6b05139 (DOI)000380730400008 ()27398775 (PubMedID)
Funder
Marcus and Amalia Wallenberg FoundationSwedish Research CouncilKnut and Alice Wallenberg Foundation, KAW-2013.0020
Available from: 2016-08-31 Created: 2016-08-31 Last updated: 2017-08-16Bibliographically approved

Open Access in DiVA

fulltext(1388 kB)75 downloads
File information
File name FULLTEXT01.pdfFile size 1388 kBChecksum SHA-512
7a83f6ebea066f21a36b9ad320af9613c52a6b212b457152badeac09d6144d82d9b09e176c253c8c79c787e0fc1bb0241180c9cd3caf88c75dbb01b04e88378c
Type fulltextMimetype application/pdf

Search in DiVA

By author/editor
Guo, Meiyuan
By organisation
Theoretical Chemistry
Theoretical ChemistryPhysical Chemistry

Search outside of DiVA

GoogleGoogle Scholar
Total: 75 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Total: 868 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf