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Understanding The Electronic Structure of Transition Metal Complexes Through XANES and RIXS

Understanding The Electronic Structure of Transition Metal Complexes Through XANES and RIXS. Kaan Atak Bodrum , September 3, 2019. Outline. Introduction Experimental and Theoretical Methods A Recent Application Electronic structure of aqueous [Co( bpy ) 3 ] 2+ and [Co( bpy ) 3 ] 3+

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Understanding The Electronic Structure of Transition Metal Complexes Through XANES and RIXS

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  1. Understanding The Electronic Structure of Transition Metal Complexes Through XANES and RIXS KaanAtak Bodrum, September 3, 2019

  2. Outline • Introduction • Experimental and Theoretical Methods • A Recent Application • Electronic structure of aqueous [Co(bpy)3]2+ and[Co(bpy)3]3+ • Summary | Understanding The Electronic Structure of Transition Metal Complexes Through XANES and RIXS | KaanAtak, 3.9.2019

  3. Cobalt TM-complexes in catalysis Example for ‘Co’ centric systems: electron mediators in a dye sensitized solar cell W. Xiang, et. al, Energy Environ. Sci., 2012, 6, 121–127. . [Co(bpy-pz)3]2+/3+ [Co(bpy)3]2+/3+ [Co(phen)3]2+/3+ Soft X-rays [Co(CN)6]3− [Co(bpy)3]2+ and[Co(bpy)3]3+ | Understanding The Electronic Structure of Transition Metal Complexes Through XANES and RIXS | Kaan Atak, 3.9.2019

  4. A biologically relevant Co TM-complex Example for ‘Co’ centric systems- Cobalamin (B12) The central Co3+ ion is vital for biological activity. The alpha position (R) can bind to CN–, OH, CH3, and 5-deoxyadenosyl ligands. | Understanding The Electronic Structure of Transition Metal Complexes Through XANES and RIXS | Kaan Atak, 3.9.2019

  5. Several core-level spectroscopic methods Non-radiative decay Radiative decay Resonant X-ray absorption (XAS/XANES) Resonant inelastic X-ray scattering (RIXS) Resonant Auger-electron emission (RPE) Normal Auger-electron emission Non-resonant/X-ray emission Core-level photoemission | Understanding The Electronic Structure of Transition Metal Complexes Through XANES and RIXS | Kaan Atak, 3.9.2019

  6. A third generation synchrotron and a soft X-ray beamline A soft X-ray beamline: U49/2 PGM-1 (70 – 1500 eV) • Radiation Characterized by • High photon flux (1013 photons/s) • 80 X 22 μm2 • Energy resolution (wavelength dependent) Image: HZB Webpage | Understanding The Electronic Structure of Transition Metal Complexes Through XANES and RIXS | Kaan Atak, 3.9.2019

  7. A free electron laser in the soft X-ray regime • based on self-amplified spontaneous emission (SASE) • bunch pattern allows precise pump probe measurements New Journal of Physics, 2010, 12, 035002 https://flash.desy.de/ | Understanding The Electronic Structure of Transition Metal Complexes Through XANES and RIXS | Kaan Atak, 3.9.2019

  8. An endstation capable of XANES/RIXS applied to liquids Sample mounting techniques Liquid jet Flow cell Journal of Large-scale Research Facilities ,2016, Vol 2, page 80 | Understanding The Electronic Structure of Transition Metal Complexes Through XANES and RIXS | Kaan Atak, 3.9.2019

  9. First principles computational methods WIREs Comput Mol Sci, 2018, Vol 8, 1759 | Understanding The Electronic Structure of Transition Metal Complexes Through XANES and RIXS | Kaan Atak, 3.9.2019

  10. Octahedral splitting in strong ligand field [Co(bpy)3]2+ [Co(bpy)3]3+ | Understanding The Electronic Structure of Transition Metal Complexes Through XANES and RIXS | Kaan Atak, 3.9.2019

  11. Aqueous [Co(bpy)3]2+ and [Co(bpy)3]3+ [Co(bpy)3]2+ - two spin possibilities for the valence d7 configuration. LS with t2g6 eg1 and HS with t2g5 eg2 . The uneven occupation in the eg level causes strong Jahn-Teller distortions for LS case. [Co(bpy)3]3+ - three different spin possibilities. LS with t2g6 and eg0 HS with t2g4 and eg2 . [Co(bpy)3]2+ [Co(bpy)3]3+ Inorganic Chemistry, 2019, Vol 58, pages 4731-4740 | Understanding The Electronic Structure of Transition Metal Complexes Through XANES and RIXS | Kaan Atak, 3.9.2019

  12. Co L-edge RIXS of [Co(bpy)3]2+ and[Co(bpy)3]3+ [Co(bpy)3]2+ • Co L-edge RIXS maps showing dd and CT emission following a 2p3d excitation. • In the [Co(bpy)3]2+ case, both possible spin states are open shell. • The [Co(bpy)3]3+ case, spin state is not purely LS (zero spin), a HS component must be considered [Co(bpy)3]3+ Inorganic Chemistry, 2019, Vol 58, pages 4731-4740 | Understanding The Electronic Structure of Transition Metal Complexes Through XANES and RIXS | Kaan Atak, 3.9.2019

  13. Co L-edge PFY-XA spectra [Co(bpy)3]2+ [Co(bpy)3]3+ • Partial fluorescence yield mode X-ray absorption (PFY- XA) spectra obtained by integrating the Co L-edge RIXS maps Inorganic Chemistry, 2019, Vol 58, pages 4731-4740 | Understanding The Electronic Structure of Transition Metal Complexes Through XANES and RIXS | Kaan Atak, 3.9.2019

  14. Co L-edge PFY-XA spectra comparison with theory [Co(bpy)3]2+ [Co(bpy)3]3+ • [Co(bpy)3]2+ ≈ 43% of low spin (S0.5) and 57% of high spin (S1.5) • [Co(bpy)3]3+ ≈ 80% of low spin (S0) and 20% of high spin (S2) Inorganic Chemistry, 2019, Vol 58, pages 4731-4740 | Understanding The Electronic Structure of Transition Metal Complexes Through XANES and RIXS | Kaan Atak, 3.9.2019

  15. N K-edge RIXS of [Co(bpy)3]2+ and [Co(bpy)3]3+ [Co(bpy)3]2+ • RIXS/X-ray emission after ligand 1s 2p excitation. • Main emission from ligand 2p orbitals. A special feature is seen on the high energy emission side marked by dotted blue line. • Both systems exhibit fluorescence features above B4 and B4 [Co(bpy)3]3+ Inorganic Chemistry, 2019, Vol 58, pages 4731-4740 | Understanding The Electronic Structure of Transition Metal Complexes Through XANES and RIXS | Kaan Atak, 3.9.2019

  16. N K-edge PFY-XA spectra [Co(bpy)3]3+ [Co(bpy)3]2+ • PFY- XA spectra obtained by integrating the N K-edge RIXS maps Inorganic Chemistry, 2019, Vol 58, pages 4731-4740 | Understanding The Electronic Structure of Transition Metal Complexes Through XANES and RIXS | Kaan Atak, 3.9.2019

  17. N K-edge PFY-XA spectra comparison with theory [Co(bpy)3]2+ [Co(bpy)3]3+ • Sensitivity towards metal spin state is minimum from the ligand side. • B2 and B2 – N 1s→π* characteristic C=N π* unoccupied orbitals. • B5 and B5 – σ* shape resonance Inorganic Chemistry, 2019, Vol 58, pages 4731-4740 | Understanding The Electronic Structure of Transition Metal Complexes Through XANES and RIXS | Kaan Atak, 3.9.2019

  18. Summary • Synchrotrons and FELs are accelerator based photon sources • X-rays produced in these photon sources can probe matter to shed light into its electronic structure • TM complexes constitute a large portion of catalytically and biologically relevant molecules • XANES and RIXS are photon-in photon-out spectroscopic methods • We probed cobalt trisbipyridine complexes using XANES and RIXS • It is observed that these complexes exhibit multiple spin state behavior | Understanding The Electronic Structure of Transition Metal Complexes Through XANES and RIXS | Kaan Atak, 3.9.2019

  19. Thank you for your attention! Acknowledgements Dr. Bernd Winter Department of Molecular Physics, Fritz-Haber-Institutder Max-Planck-Gesellschaft, Berlin ,Germany Dr. SreejuSreekantan Nair Lalithambika Freie Universität Berlin, Fachbereich Physik, Berlin, Germany Dr. Ronny Golnak Helmholtz-Zentrum Berlin fürMaterialien und Energie, Department of Highly Sensitive X-ray Spectroscopy, Berlin, Germany Prof. Simone Techert DeutschesElektronen-Synchrotron DESY, Structural Dynamics in Chemical Systems, Hamburg, Germany

  20. Kaan Atak Structural Dynamics in Chemical Systems kaan.atak@desy.de

  21. N K-edge experimental and theoretical X-ray emission • Experimental XES at 406.4 eV compared with calculated XES. • The emission from pink shaded area • originates from metal-ligand mixed orbitals. • [Co(bpy)3]2+ with 53.5% metal 3d t2g [Co(bpy)3]3+ 30% 3d t2g Lalithambika et al. Inorganic Chemistry, 2019, Vol 58, pages 4731-4740 | Understanding The Electronic Structure of Transition Metal Complexes Through XANES and RIXS | Kaan Atak, 3.9.2019

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