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Time resolved structural investigations of soft condensed matter André Rossberg, Satoru Tsushima

Time resolved structural investigations of soft condensed matter André Rossberg, Satoru Tsushima Helmholtz Zentrum Dresden-Rossendorf Dresden and Rossendorf Beamline (ROBL), ESRF, Grenoble. Methods for liquids and amorphous materials. Extended fine structure spectroscopy (EXAFS)

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Time resolved structural investigations of soft condensed matter André Rossberg, Satoru Tsushima

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  1. Time resolved structural investigations of soft condensed matter André Rossberg, Satoru Tsushima Helmholtz Zentrum Dresden-Rossendorf Dresden and Rossendorf Beamline (ROBL), ESRF, Grenoble

  2. Methods for liquids and amorphous materials • Extended fine structure spectroscopy (EXAFS) • For metal complexes in solution, etc. • Local atomic environment (interatomic distances, coordination numbers, type of the atoms, static and thermal disorder) • 2. Wide angle scattering (“PDF method”) • For substrates (nano sized particles, x-ray amorphous) which may adsorb metal complexes at the surface, metal complexes in solution, etc. • Measuring of all pair distribution functions (PDF or g(r))

  3. FL Detector μ(E) E M2 DCM I2 I1 sample I0 M1 Q(Å-1) Actinides (L-edges) 16-30 keV μ(E) = ln (I0/I1) = μ0(E) { 1 + (k) } • g(r) by shell fit or inverse method • 1 h for ideal conditions • g(r) only up to 6 Å • Few seconds • g(r) direct accessible • For solutions much higher • concentrations necessary • Lower resolution in g(r) but up to high r 2θ F(Q) Q=4π/λ sinθ

  4. Available photons per 10mm2 at ROBL (before reconstruction) Irradiated area of 10mm2 - typical for EXAFS sample For reliable EXAFS spectra one may calculate the necessary x-ray shots in dependence on the intended time resolution for time resolved studies… Si Pt Actinides: 6x1010 photons/s/10mm2

  5. Time resolved studies • Sampling time of an EXAFS photoelectron is ~0.1 fs much shorter than the atomic vibrational periods ~0.1 ps ! EXAFS samples a unidimensional distribution of instantaneous interatomic distances for each coordination shell of the absorber atom Dalba, G. & Fornasini, P. (1997). J. Synchrotron Rad. 4, 243-255.

  6. Monitoring structural (EXAFS, PDF) and electronical changes (XANES) for very fast processes like transition states of metal complexes, atomic vibrations Structures of the ground state and the lowest-lying triplet states of bare UO22+ ion at the CASPT2 level Excited states 3g U-O 1.75 Å 1g U-O 1.78 Å Absorption 3g U-O 1.77 Å Emission 1g U-O 1.78 Å Ground state U-O 1.99 Å, 1.71 Å 3g U-O 2.01 Å, 1.72 Å 3g 1g U-O 1.700 Å spin density of 3g (uf) U-O 0.05 - 0.3 Å EXAFS: ±0.02 Å strong hydrogen acceptor Oax U Oax Real et al. J. Chem. Phys. 127, 214302 (2007). Real et al.J. Am. Chem. Soc. 130, 11742, (2008).

  7. Photochemical reaction proceeds via axial oxygen linkage Reactivity of uranyl oxygens (2010-) P.L.Arnold et al. Nature Chem. 2, 1056 (2010). P.L.Arnold et al. Angew. Chem.Int.Ed. 50, 887 (2011). A.Yahia et al. Chem. Eur. J. 16,4881, (2010). G.Nocton et al. JACS 132, 495, (2010). V.Mougel et al. Chem.Eur.J. 16, 14365 (2010). S.Fortier & T.W.Hayton Coord.Chem.Rev. 254, 197 ( 2010). J.L.Brown et al. JACS 132, 7248 (2010). M.Bühl, G.Schreckenbach, Inorg. Chem. 49, 3821 (2010). Z.Szabó, I.Grenthe, Inorg. Chem., 49, 4928 (2010). S. Kannan et al. JACS, 128, 14024 (2006). Photochemical reduction of UO22+ Complex mechanisms: - methanol Quantum yield (U4+) > 0.5 - oxalate U(IV), CO2 (weakly acidic) U(VI), CO2, CO (acidic) UO22+/H2O/ organic substances U4+/H2O/ byproducts

  8. Ground states and lowest-lying triplet states of UO22+ linked with methanol and H2O GS TS Theoretical EXAFS spectra (U LIII edge) GS TS TS GS TS High power UV-Vis pump and TR-EXAFS S.Tsushima, Inorg. Chem., 48, 4856 (2009).

  9. Picosecond transient absorption spectroscopy of UO22+ nitrate in water and in methanol water methanol R.Ghosh, J.A.Mondal, H.N.Ghosh, D.K.Palit, J. Phys. Chem. A 114, 5263 (2010).

  10. UO22+ / H2O / oxalate It is well-known that uranyl oxalate can decompose under the influence of light. (chemical actinometer) Brits et al. correlated photodecomposition of uranyl oxalate with UO2(C2O4)22- (1:2). However, speciation calculation suggests the prevalence of 1:3 and 2:5 species under the experimental condition of Brits et al.. Uranyl oxalate 1:3 complex A. G. Brits, R. Van Eldik and J. A. Van Den Berg, Z. Physik. Chem. Neu Folge, 99, 107 (1976). A. G. Brits, R. Van Eldik and J. A. Van Den Berg, Z. Physik. Chem. Neu Folge, 102, 203 (1976). A. G. Brits, R. Van Eldik and J. A. Van Den Berg, Z. Physik. Chem. Neu Folge, 102, 213 (1976). A.G. Brits, R. Van Eldik and J.A. Van Den Berg, J. Inorg. Nucl. Chem., 39, 1195 (1977). A. G. Brits, R. Van Eldik and J. A. Van Den Berg, Inorg. Chim. Acta, 30, 17 (1978).

  11. Uranyl Oxalate 1:3 complex Density functional theory (DFT ) calculations decarboxylation 2.49 2.35 2.63 2.46 2.40 2.46 2.50 CO2 2.41 2.41 2.41 U=O 1.85 U=O 1.79 ground state triplet excited state (bond distances in Å) S.Tsushima, V.Brendler, K.Fahmy, Dalton Trans., 39, 10953 (2010).

  12. In case of asymmetric g(r) breakdown of the EXAFS shell fit model Integral kernel: , where Condensed form: • Inversion of the EXAFS integral equation necessary to get n(r) • Fredholm integral equation of the first kind • Integral kernel ill conditioned ill posed problem • Solution with inverse method • For EXAFS Landweber Iteration [1] was tested and is now used [2] [1] Landweber L. Am. J. Math. Manag. Technol. 1951, 73, 615. [2] Rossberg, A. & Funke, H. (2010). Journal of Synchrotron Radiation 17, 280-288.

  13. Summary • Structural and electronical characterization of excited states of metal complexes • Proof of DFT prediction • study of reaction mechanisms (photochemistry) • One need pump and probe experiment (time: ps to fs) Outlook (some other ideas) • Tunable IR Laser, pump and probe experiment single g(r) peaks may change the form due to excitation of vibrational modes = identification of groups, type of atoms,… • Metal complexes (with dipol) in strong electric field (short time) = orientation = 3d structural information by using polarized beam

  14. Acknowledgements Dr. Harald Funke Dr. Karim Fahmy Dr. Vinzenz Brendler Prof. Dr. Thomas E. Cowan Zentrum für Informationsdienste und Hochleistungsrechnen, Technische Universität Dresden Thank you for your attention !!

  15. Pitfall of DFT Potential energy curves of the UO22+ ion as a function of one U–Oyl bond computed with (a)CCSD and (b) TD-DFT B3LYP. (F.Réal , V.Vallet, C.Marian, U.Wahlgren J. Chem. Phys. 127, 214302 (2007)) DFT is not the best method to study excited states of uranyl(VI). CASPT2 vs TD-DFT K.Pierloot, E.van Besien, J. Chem. Phys. 123, 204309 (2005). K.Pierloot, E.van Besien, E. van Lenthe, E. J. Baerends, J.Chem. Phys. 126, 194311 (2007).

  16. 1. UO22+ / H2O / methanol Method and molecular models H2O MeOH UO2(H2O)52+ UO2(H2O)52+ Theory: Hybrid DFT (B3LYP) Program: Gaussian 03 Solvent: CPCM Basis sets: ECP on U, O, C and 6-311++G** on H

  17. Structures of the ground state and the lowest-lying triplet states of bare UO22+ ion at the CASPT2 level Excited states 3g U-O 1.75 Å 1g U-O 1.78 Å Absorption 3g U-O 1.77 Å Emission 1g U-O 1.78 Å Ground state U-O 1.99 Å, 1.71 Å 3g U-O 2.01 Å, 1.72 Å 3g 1g U-O 1.700 Å U-O 0.05 - 0.3 Å EXAFS: ±0.02 Å strong hydrogen acceptor spin density of 3g (uf) Real et al. J. Chem. Phys. 127, 214302 (2007). Real et al.J. Am. Chem. Soc. 130, 11742, (2008).

  18. electron transfer U(V) U(VI) Spin density of the lowest-lying triplet states of UO2(OH2)52+ linked with MeOH and H2O CH3OH (with alcohol) H2O (no alcohol) 0.88 triplet 1.96 1.06 S.Tsushima, Inorg. Chem., 48, 4856 (2009).

  19. Structure and spin density of the lowest-lying triplet state of UO2(C2O4)34- Photoreduction Decarboxylation U(VI) U(V) CO2 gas S.Tsushima, V.Brendler, K.Fahmy, Dalton Trans., 39, 10953 (2010).

  20. 3. Quenching of uranium(VI) luminescence by ions and molecules Luminescence (no quenching) Invisible luminescence (quenching) Photoreduction (quenching) UO2 1.93 F 0.07 UO2 1.05 MeOH 0.95 UO2 1.55 Cl 0.46 3B2 U-F 2.08Å Dissociative (quenching) 2.12 eV (585nm) UO2 0.98 I 1.00 1A1 U-F 2.09Å 3B1 U-I 3.78Å 0.01 eV 1A1 U-I 3.00Å Geometries and Mulliken spin densities - of the lowest-lying triplet states of UO22+ aquo ion associated with F, Cl, I, and methanol. S.Tsushima, C.Götz, K.Fahmy, Chem.Eur.J.. 16, 8029 (2010).

  21. Alternative mechanism at low pH CO2 . HC2O4- HO-CO0 OCOH- excitation de-excitation 1.51Å 2.47Å 2.07Å -112kJ/mol decarboxylation UO22+(aq) UO2+(aq) UO22+(aq) -2kJ/mol OH- CO no reduction of U(VI) production of CO and OH- Byproducts: U(VI), CO2, CO (acidic) U(IV), CO2 (weakly acidic) UO22+(aq) S.Tsushima, V.Brendler, K.Fahmy, Dalton Trans., 39, 10953 (2010).

  22. Photochemical byproduct can reduce another set of UO22+ spin density spin density HCHO formaldehyde UVOOH2+(aq) -122 kJ/mol UVIO22+(aq) 0 kJ/mol S.Tsushima, Inorg. Chem., 48, 4856 (2009). Why (U4+) > 0.5?

  23. Dimeric species (2:5) Solid:J. Leciejewicz, N. W. Alcock, T. J. Kemp, Struct. Bonding, 82, 43 (1995). Acetone:C. Görller-Walrand, K.Servaes, Helv. Chim. Acta, 92, 2304 (2009). Aqueous:J. Havel, J. Soto-Guerrero, P. Lubal, Polyhedron, 21, 1411, (2002). or U-U 6.50Å EXAFS cannot differentiate 1:3 and 2:5 HEXS

  24. (unit in Ångströms) Lowest-lying triplet states 1:2 1.85 1:1 2.33 2.40 2.30 1.85 1.83 1.83 2.30 decarboxylation decarboxylation 1.85 2.61 2.63 1.85 1:3 2:5 S.Tsushima, V.Brendler, K.Fahmy, Dalton Trans., 39, 10953 (2010).

  25. Uranyl oxalate ground state structures 1:2 1:1 1:3 EXAFS and DFT V. Vallet, H. Moll, U.Wahlgren, Z.Szabo, I.Grenthe, Inorg. Chem., 42, 1982 (2003).

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