Text optional: Institutsname Prof. Dr. Hans Mustermann www.fzd.de Mitglied der Leibniz-Gemeinschaft André Rossberg | Institute of Radiochemistry | http://www.hzdr.de
Time resolved structural investigations of soft condensed matter
André Rossberg, Satoru Tsushima
Helmholtz Zentrum Dresden-Rossendorf Dresdenand Rossendorf Beamline (ROBL), ESRF, Grenoble
Page 2André Rossberg | Institute of Radiochemistry | http://www.hzdr.de
Methods for liquids and amorphous materials
1.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))
Page 3André Rossberg | Institute of Radiochemistry | http://www.hzdr.de
I2 I1 I0
DCM
M1
M2
FL Detector
sampleμ(E) = ln (I0/I1)
= μ0(E) { 1 + (k) }
Q=4π/λ sinθ
2θ
Q(Å
-1)
32
, 2χ exp sin 2 2δ , d
λ
F k r rk kr k k r V
kr kg r
F(Q)
Actinides (L-edges) 16-30 keV
g(r) by shell fit or inverse method1 h for ideal conditionsg(r) only up to 6 Å
Few secondsg(r) direct accessibleFor solutions much higher concentrations necessaryLower resolution in g(r) but up
to high r
E
μ(E
)
Page 4André Rossberg | Institute of Radiochemistry | http://www.hzdr.de
Available photons per 10mm2 at ROBL (before reconstruction)
0 5 10 15 20 25 30 35
2.0x1010
4.0x1010
6.0x1010
8.0x1010
1.0x1011
1.2x1011
1.4x1011
Ph
oto
n F
lux
[ph
/s/1
0mm
2 ]
Photon Energy [keV]
Si
Pt
Actinides: 6x1010 photons/s/10mm2
Irradiated area of 10mm2 - typical for EXAFS sample
For reliable EXAFS spectraone may calculate the necessary x-ray shots in dependence on the intended time resolution for time resolved studies…
Page 5André Rossberg | Institute of Radiochemistry | http://www.hzdr.de
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
2( )
4
dNg r
r dr
Dalba, G. & Fornasini, P. (1997). J. Synchrotron Rad. 4, 243-255.
Page 6André Rossberg | Institute of Radiochemistry | http://www.hzdr.de
Monitoring structural (EXAFS, PDF) and electronical changes (XANES) for very fast processes like transition states of metal complexes, atomic vibrations
U-O
Ground state
Excited states
1g
0.05 - 0.3 ÅEXAFS: ±0.02 Å
AbsorptionEmission
3g
U-O 1.700 Å
U-O 1.75 Å
3gU-O 2.01 Å, 1.72 Å
spin density of 3g (uf)
1g U-O 1.78 Å3g U-O 1.77 Å1g U-O 1.78 Å3g
U-O 1.99 Å, 1.71 Å
strong hydrogen acceptor
Real et al. J. Chem. Phys. 127, 214302 (2007).Real et al. J. Am. Chem. Soc. 130, 11742, (2008).
Oax U Oax
Structures of the ground state and the lowest-lying triplet states of bare UO2
2+ ion at the CASPT2 level
Page 7André Rossberg | Institute of Radiochemistry | http://www.hzdr.de
Photochemical reduction of UO22+
UO22+/H2O/
organic substancesU4+/H2O/byproducts
Complex mechanisms:- methanol
- oxalateQuantum yield (U4+) > 0.5
U(IV), CO2 (weakly acidic) U(VI), CO2, CO (acidic)
Photochemical reaction proceedsvia axial oxygen linkage
S. Kannan et al. JACS, 128, 14024 (2006).
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).
Reactivity of uranyl oxygens (2010-)
M.Bühl, G.Schreckenbach, Inorg. Chem. 49, 3821 (2010).Z.Szabó, I.Grenthe, Inorg. Chem., 49, 4928 (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).
Page 8André Rossberg | Institute of Radiochemistry | http://www.hzdr.de
Ground states and lowest-lying triplet states of UO2
2+ linked with methanol and H2OGS
GS
TS
TS
High power UV-Vis pump and TR-EXAFS
Theoretical EXAFS spectra (U LIII edge)
S.Tsushima, Inorg. Chem., 48, 4856 (2009).
2 4 6 8 10 12 14 16
-4
-2
0
2
4
6
8
10
12
14
16
18
20
(k)
*k3
k [Å-1]
0 1 2 3 4
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
3.2
FT
R + R [Å]
GS
TS
TS
Page 9André Rossberg | Institute of Radiochemistry | http://www.hzdr.de
R.Ghosh, J.A.Mondal, H.N.Ghosh, D.K.Palit, J. Phys. Chem. A 114, 5263 (2010).
Picosecond transient absorption spectroscopyof UO2
2+ nitrate in water and in methanol
water
methanol
Page 10André Rossberg | Institute of Radiochemistry | http://www.hzdr.de
It is well-known that uranyl oxalate can decompose under the influence of light. (chemical actinometer)
UO22+ / H2O / oxalate
Brits et al. correlated photodecomposition of uranyl oxalate with UO2(C2O4)2
2- (1:2). However, speciation calculation suggests the prevalence of 1:3 and 2:5 species under the experimental condition of Brits et al..
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).
Uranyl oxalate 1:3 complex
Page 11André Rossberg | Institute of Radiochemistry | http://www.hzdr.de
Uranyl Oxalate 1:3 complex
decarboxylation
S.Tsushima, V.Brendler, K.Fahmy, Dalton Trans., 39, 10953 (2010).
2.40
2.412.41
2.41
2.35
2.46
2.49
2.46 2.50
ground state triplet excited state
2.63
U=O 1.85
(bond distances in Å)
U=O 1.79
CO2
Density functional theory (DFT ) calculations
Page 12André Rossberg | Institute of Radiochemistry | http://www.hzdr.de
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]
In case of asymmetric g(r) breakdown of the EXAFS shell fit model
32
, 2χ exp sin 2 2δ , d
λ
F k r rk kr k k r g r V
kr k
2 22
1
( , ) 2χ exp exp 2 sin 2 2δ , .
λ
shellsm m m m
m m mm m
N F k r rk k kr k k r
r k k
2.0 2.2 2.4 2.6 2.8 3.0
0.0
0.1
0.2
g(r
)
r [Å]
2
, 2( , ) exp sin 2 2δ ,
λ
F k r rA k r kr k k r
kr k
Integral kernel:
0
χ , d
k k r n rA r
[1] Landweber L. Am. J. Math. Manag. Technol. 1951, 73, 615.
[2] Rossberg, A. & Funke, H. (2010). Journal of Synchrotron Radiation 17, 280-288.
2( )) 4 ( rn g rrCondensed form: , where
Page 13André Rossberg | Institute of Radiochemistry | http://www.hzdr.de
• 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)
Summary
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
Page 14André Rossberg | Institute of Radiochemistry | http://www.hzdr.de
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 !!
Page 15André Rossberg | Institute of Radiochemistry | http://www.hzdr.de
Page 16André Rossberg | Institute of Radiochemistry | http://www.hzdr.de
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).
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).
CASPT2 vs TD-DFT
Pitfall of DFT
Page 17André Rossberg | Institute of Radiochemistry | http://www.hzdr.de
Method and molecular models
H2OMeOH
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
1. UO22+ / H2O / methanol
Page 18André Rossberg | Institute of Radiochemistry | http://www.hzdr.de
Structures of the ground state and the lowest-lying triplet states of bare UO2
2+ ion at the CASPT2 level
U-O
Ground state
Excited states
1g
0.05 - 0.3 ÅEXAFS: ±0.02 Å
AbsorptionEmission
3g
U-O 1.700 Å
U-O 1.75 Å
Real et al. J. Chem. Phys. 127, 214302 (2007).Real et al. J. Am. Chem. Soc. 130, 11742, (2008).
3gU-O 2.01 Å, 1.72 Å
spin density of 3g (uf)
1g U-O 1.78 Å3g U-O 1.77 Å1g U-O 1.78 Å3g
U-O 1.99 Å, 1.71 Å
strong hydrogen acceptor
Page 19André Rossberg | Institute of Radiochemistry | http://www.hzdr.de
Spin density of the lowest-lying triplet states of UO2(OH2)5
2+ linked with MeOH and H2O
S.Tsushima, Inorg. Chem., 48, 4856 (2009).
1.06
0.88
1.96
H2O(no alcohol)
CH3OH(with alcohol)
tripletelectron transfer
U(V) U(VI)
Page 20André Rossberg | Institute of Radiochemistry | http://www.hzdr.de
Decar
boxyla
tion
U(VI) U(V)
CO2 gas
Photoreduction
S.Tsushima, V.Brendler, K.Fahmy, Dalton Trans., 39, 10953 (2010).
Structure and spin density of the lowest-lying triplet state of UO2(C2O4)3
4-
Page 21André Rossberg | Institute of Radiochemistry | http://www.hzdr.de
3. Quenching of uranium(VI) luminescence by ions and molecules
Luminescence(no quenching)
UO2 1.93F 0.07
Invisible luminescence(quenching)
UO2 1.55Cl 0.46
Photoreduction(quenching)
Dissociative(quenching)
UO2 1.05MeOH 0.95
UO2 0.98I 1.00
Geometries and Mulliken spin densities - of the lowest-lying triplet states of UO2
2+ aquo ion associated with F, Cl, I, and methanol.
S.Tsushima, C.Götz, K.Fahmy, Chem.Eur.J.. 16, 8029 (2010).
2.12 eV(585nm)
U-F 2.08Å 3B2
1A1 U-F 2.09Å
0.01 eV
U-I 3.78Å 3B1
1A1 U-I 3.00Å
Page 22André Rossberg | Institute of Radiochemistry | http://www.hzdr.de
excitation
decarboxylation
de-excitation
COOH-
1.51Å 2.47Å2.07Å -112kJ/mol
-2kJ/mol
UO22+(aq) UO2
+(aq)
HC2O4-
HO-CO0.
OCOH-
UO22+(aq)
UO22+(aq)
no reduction of U(VI)production of CO and OH-
S.Tsushima, V.Brendler, K.Fahmy, Dalton Trans., 39, 10953 (2010).
Alternative mechanism at low pH
Byproducts: U(VI), CO2, CO (acidic) U(IV), CO2 (weakly acidic)
CO2
Page 23André Rossberg | Institute of Radiochemistry | http://www.hzdr.de
Why (U4+) > 0.5?
HC
HOH
0 kJ/mol
spin density
UVIO22+(aq)
S.Tsushima, Inorg. Chem., 48, 4856 (2009).
HCHO formaldehyde
-122 kJ/mol
spin density
UVOOH2+(aq)
Photochemical byproduct can reduce another set of UO2
2+
Page 24André Rossberg | Institute of Radiochemistry | http://www.hzdr.de
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
Page 25André Rossberg | Institute of Radiochemistry | http://www.hzdr.de
Lowest-lying triplet states
1:1
1:2
1:3 2:5
decarboxylation decarboxylation
S.Tsushima, V.Brendler, K.Fahmy, Dalton Trans., 39, 10953 (2010).
2.63
1.85
2.301.83
2.301.83
1.85
1.85
1.85
2.332.40
2.61
(unit in Ångströms)
Page 26André Rossberg | Institute of Radiochemistry | http://www.hzdr.de
1:11:2
1:3
V. Vallet, H. Moll, U.Wahlgren, Z.Szabo, I.Grenthe, Inorg. Chem., 42, 1982 (2003).
Uranyl oxalate ground state structures
EXAFS and DFT