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Advanced X-Ray Spectroscopy Advanced X-ray Spectroscopy Serena DeBeer Penn State Bioinorganic Workshop Max-Planck-Institut für Chemische Energiekonversion June 2016 Understanding Catalytic Connections... Key Reactions in Energy Research heterogeneous catalysts How can sustainable, earth-abundant base metals enable the activation of homogeneous biological strong chemical bonds? catalysts catalysts Requires an atomic level understanding of the geometric and electronic structure changes which occur over the course of catalysis. X-ray Spectroscopy X-ray Absorption Spectroscopy 4p (XAS) 3d 2p Energy (eV) 2s X-ray Emission Energy Spectroscopy 3p (XES) 2s/2p Kα1 Kβ1,3 Kα2 Kβ2,5 1s Kβ” Metal Ligand Kβ’ Intensity Energy (eV) A High-Energy Resolution XES Setup The increased resolution of modern setups, increased sensitivity and developments in theory have opened up all new chemical applications… Glatzel, P.; Bergmann, U. Coord. Chem. Rev 2005, 249, 65. Smolentsev, G.; Soldatov, A. V.; Messinger, J.; Merz, K.; Weyhermueller, T.; Bergmann, U.; Pushkar, Y.; Yano, J.; Yachandra, V. K.; Glatzel, P., JACS, 2009, 131, 13161. Lee, N.; Petrenko, T.; Bergmann, U.; Neese, F.; DeBeer, S., JACS, 2010, 132, 9715. Figure J. A. Rees Pushkar, Y.; Long, X.; Glatzel, P.; Brudvig, G. W.; Dismukes, G. C.; Collins, T. J.; Yachandra, V. K.; Yano, J.; Bergmann, U. ACIES, 2010, 49, 800. Lancaster, K. M.; Roemelt, M.; Ettenhuber, P.; Hu, Y.; Ribbe, M. W.; Neese, F.; Bergmann, U.; DeBeer, S. Science 2011, 334, 974. α α -SOC +SOC β β β X-Ray Emission Spectra αβ β N. Lee, T. Petrenko, U. Bergmann, F. Neese, S. DeBeer, J. Am. Chem. Soc., 2010, 132, 9715-9727. β β → → Cont. Kα Kβ Valence to Core -SOC -SOC -SOC +SOC +SOC +SOC Virt Kβ2,5 Val. , Kβ‘ x10 x1000 Kβ1,3 3s,p Kβ‘ Kα1,2 2s,p • dominated by 2p spin orbit • dominated by 3p-3d • highly sensitive to ligand 1s exchange environment • K-alpha detected XAS (1s2p RIXS) enables higher • spin state marker -SOC • measure of ligand identity, +SOC resolution ionization potential, and • enables oxidation state and protonation state spin dependent XAS • enables ligand selective XAS Outline ๏ Non-resonant X-ray Emission Spectroscopy (XES) - K-Beta XES - Valence to Core XES - (K-alpha XES) ๏ Resonant X-ray Emission Spectroscopy (RXES or RIXS) - XAS + XES 2D measurement - Higher resolution XAS - Oxidation State and Spin State Selective XAS - Ligand Selective XAS? - Combine Mb-XES instrument - 2p3d RIXS K-Beta Main Line and Valence to Core Regions Kβ Mainline V2C Kβ2,5 Kβ1,3 Kβ” Kβ’ 7 K-Beta Main Lines: A fingerprint for Spin State? ✤ High-spin Fe complexes exhibit a shoulder which is (essentially) absent in low spin analogues ✤Similar observations can be made for other metals.... ✤ Correlation first made in 1959 Tsutsumi et al., J. Phy. Soc. Jap. Vol. 14, 12 C.J. Pollock, P. T. Wolczanski, S. DeBeer, unpublished results. HS vs LS generalization for K-Beta Mainlines high-spin low-spin N. Lee, T. Petrenko, U. Bergmann, F. Neese, S. DeBeer, J. Am. Chem. Soc., 2010, 132, 9715-9727. Origins of K-Beta Main Line Splitting: HS Fe(III) 3d 3d 1s 1s 1s ionization 7S 3p-1s 5S hν 3d 3p 3d 5P 6 S 3d 3p,3d predicted Ground State exchg. 3p spectrum 5:7 ratio...BUT 7P this is not what we see... Origins of K-Beta Main Line Splitting: HS Fe(III) 4D d,d elec rep 3d 5P (4P, 4D) 3p 5 4 P P 5P (6S) 7P (6S) split by 3p, 3d exchange ~15 eV 3d The spectrum will be 6 further split by 3p spin S 3p orbit Many Electron 5 States P Origins of K-Beta Main Line Splitting: LS Fe(III) 3d 3d 1s 1s 1s ionization 3I 3p-1s 1I hν 3d 3p 3d 1H, 1I, 1K 2I 3d Ground State 3p ✦ 3p-3d exchange splitting 3 3 3 decreases H, I, K ✦splitting is closer to d-d electron repulsion Analytical Expressions for the Kβ Mainline Splittings Energy Splitting of the Mainline: Free Ion Case The mainline splitting can be expressed in terms of the p-d exchange (4G1 + 42G3) for every d-count Simple take home message - The more unpaired electrons the bigger the splitting? C. J. Pollock, M. U. Delgado-Jaime, M. Atanasov, F. Neese, S. DeBeer, J. Am. Chem. Soc., 2014, 136, 9453-9463. K-Beta Mainline and Covalency Exchange interaction scales with covalency of the 3d manifold, so ΔE dependent on 3d orbital composition C. J. Pollock, M. U. Delgado-Jaime, M. Atanasov, F. Neese, S. DeBeer, J. Am. Chem. Soc., 2014, 136, 9453-9463. Previous Observations Bergmann, et al, Coord. Chem. Rev., 2005, 249, 65. Cramer, et al, J. Synchrotron Rad., 1997, 4, 236. Urch, et al, J. Electron Spectrosc. Relat. Phenom., 2001, 113, 179. K-Beta XES to Understand the Role of the Carbon? Julian Rees’ Talk A B [(Tp)MoFe3S4Cl3]- FeMoco K-Beta Mainline of Cubanes vs. N2ases ∆E(eV) Mo 11,7 cubane V 12,0 cubane MoFe 10,7 VeFe 10,7 Lessons from Model Studies In Collaboration with F. Meyer (Göttingen) 2-/3-/4- ∆E(eV)=13.4 eV A. Albers et al., Angew. Chem. Int. Edit., 2011, 9191 (39) A. Albers et al., J. Am. Chem. Soc., 135, 2013, 1704. J. Kowalska et al., Inorg. Chem., 2016, in press. Contributions due to change in oxidation state and covalency completely cancel! K-Beta Mainline of Cubanes vs. N2ases ∆E(eV) Mo cubane 11,7 V 12,0 cubane MoFe 10,7 VeFe 10,7 2- [L2Fe(III)2S2] 13,4 3- [L2Fe(II,III)2S2] 13,4 4- [L2Fe(II)2S2] 13,4 P-cluster 13,1 MoFe/VFe smallest ∆E of any FeS cluster. Likely attributed to covalency of carbon. Se HERFD to Interrogate Intermediates T. Spatzal et al., ELife, 2015, 4:e11620 Se can place the S2B belt sulfur Se migrates to S3A and S5A at later stages of catalysis FeMoco may be more dynamic than previously thought The central carbon, may provide structural stability Kβ and Valence to Core XES of Ferric complexes Kβ Main Line Kβ Valence to Core high-spin ‣ K-Beta main line shows a strong dependence on spin 1 state (both energy and shape of spectra) ‣ Valence to core region show greater sensitivity to the chemical environment ‣ High-spin complexes show broader features and lower intensities in valence low-spin 4 to core region N. Lee, T. Petrenko, U. Bergmann, F. Neese, S. DeBeer, J. Am. Chem. Soc., 2010, 132, 9715-9727. Predicting V2C XES with DFT Calculations 2 i m j 4! ! ! ! ! 4! 2 ! " = ! = ! i m j f ! ,! ,! ( em ) em # # 2 1 em # # ! ! ! ( em ij ) 3 i j !=x,y,z 2 3 i j !=x,y,z ! ! ! "! + ! ! ! ( FI em ) 4 ! • Emission energies calculated as ∆E between one-electron Kohn-Sham orbitals • Transitions require metal character in molecular orbitals involved in the emission process • Intensity is governed by the electric dipole moment operator (mα) • Generally, observed V2C transitions arise from states involving transitions from occupied molecular orbitals possessing metal 4p character Theory ORCA F. Neese Experimental N. Lee, T. Petrenko, U. Bergmann, F. Neese, S. DeBeer, J. Am. Chem. Soc., 2010, 132, 9715-9727. Lancaster, K.M.; Finkelstein, K.D.; DeBeer, S. Inorg. Chem. 2011, 50, 6767-6774. Electronic Structural Insights from VtC XES… Cp Fe 4p 7115 2pz ✓ All contributions result from metal 3d 7110 np mixing into e1u filled Fc MOs 2px,y a2u 7105 e1u ✓ Maps out (eV) ! filled ligand MOs a2u from perspective Energy 7100 of a given metal e1u 2s 7095 Lancaster, K.M.; Finkelstein, K.D.; DeBeer, S. Inorg. Chem. 2011, 50, 6767-6774. a2u Pollock, C. J. and DeBeer, S. 2015, Accounts of Chemical Research, 48, 2967-2975. 7090 Identifying the Central Atom in FeMoco Novel Spectroscopy: Quantum Chemistry X-Ray Emission experiment Calc: X=C Calc: X=N Calc: X=O Lancaster, K.M.; Roemelt, M.; Ettenhuber, P.; Hu, Y.; Ribbe, M.W.; Neese, F.; Bergmann, U.; DeBeer, S. Science 2011, 334, 974-977. XES is directly sensitive to protonation 4.5 4.0 3.5 ✓O vs OH 2s features 3.0 separated by ~2 eV 2.5 ✓Ability to examine a single protonation event 2.0 6515 eV NormalizedIntenstiy ✓distinguishes bis-hydroxo 1.5 from O2-/H2O 1.0 6513 eV ✓Readily applicable to 0.5 complex systems without 6505 6510 6515 6520 6525 6530 6535 isotope substitution Energy (eV) Effect of protonation on the MOs…. O2- OH- 4.5 4.0 3.5 3.0 2.5 2.0 ✓ Protonation lowers the 2s NormalizedIntenstiy 1.5 energy ✓ Delocalizes electrons into 1.0 the O-H bond, thus lowering 0.5 intensity 6505 6510 6515 6520 6525 6530 6535 Similarly a lower energy ✓ Energy (eV) shoulder appears in the KB2,5 Outline ๏ Non-resonant X-ray Emission Spectroscopy (XES) - K-Beta XES - Valence to Core XES - (K-alpha XES) ๏ Resonant X-ray Emission Spectroscopy (RXES or RIXS) - XAS + XES 2D measurement - Higher resolution XAS - Oxidation State and Spin State Selective XAS - Ligand Selective XAS? - Combine Mb-XES instrument - 2p3d RIXS RIXS: Adding Another Dimension... energy transfer [eV] incident energy [eV] ✴L-edge like probe with hard X-rays! ✴Expands in situ possibilities (high pressure, solutions, etc) ✴Reduced damage 1s2p RIXS: Applications to the OEC ✴Readily applied to complex systems in situ ✴Able to obtain data on dilute metalloprotein ✴provides a much more detailed “fingerprint” for the assignment of oxidation states within complex systems. ✴BUT, more theory development is needed for proper treatment (ROCIS in progress) ✴Cuts through RIXS plane can provide higher resolution XANES... Glatzel et al., Inorg. Chem, 2013, 52, 5642. Standard vs High-Resolution XAS Detection In the dilute limit XAS is measured as proportional to fluorescence Total fluorescence detection: Resultant XAS Spectrum: Kα 2p-1s Scatter Kβ 3p-1s Energy, eV Energy, eV K.
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