Speciation of actinides and lanthanides in ionic liquids by XASAt INE, on Cm 3+ in IL Gives number and nature of fluorescent species in solution (Eu, Cm) combined with “French”

Speciation of actinides and lanthanides in ionic liquids by XAS

IPHC, IPNL, MSM labI. Billard, C. Gaillard, A. Ouadi, S. Georg, V. MazanO. Klimchuk, E. Jobin, S. Mekki , S. StumpfO. Klimchuk, E. Jobin, S. Mekki , S. StumpfG. Wipff, A. Chaumont, R. Schurhammer

INE (FZK), M. Denecke, K. Dardenne, P. PanakROBL (FZR)C. Hennig

French-German seminar, Strasbourg, 22-23 February 2012

with the financial help of EURATOM, ACTINET, GnR PARIS, ANR

Studies led in the frame of nuclear fuel reprocessingIL use in replacement of organic solvents (kerosene) or for electrodeposition

→→→→ IL are easy to handle, non flammable, non toxic, non volatile

Work purpose

Which IL? Hydrophobic and stable in presence of water

N

N

C H3

NS S C F3

OO

F 3C

Need for fundamental data on solute-solvent and solute-solute interactions in IL

C4mimTf2N, (TfO-, PF6-, BF4

-)

NOO

F 3C

C H3

French�German collaboration, what for?

� EXAFS experimentsOn ROBL (ESRF, for uranium), on INE-BL (americium) and XAS-BL (europium) (ANKA, Karlsruhe)

Gives an average speciation of f-elements in IL samples (nature, number and distance of close neighbours)

� TRLFS experiments

To get speciation of f-elements in IL samples, by combination of spectroscopic techniques

� TRLFS experimentsAt INE, on Cm3+ in IL

Gives number and nature of fluorescent species in solution (Eu, Cm)

� combined with “French” data, obtained by UV-vis spectroscopy, TRLFS (Eu) and theoretical (MD) calculations

Dried IL solutions (< 1 H2O / An-Ln)

Solvatation of U(VI) in IL

In water: [UO2(H2O)5]2+

In IL?� Various U(VI) salts in C4mimTf2N

0

10

20

30

40

50

350 370 390 410 430 450 470 490

ε(m

ol-1

.cm

-1)

λ (nm)

UO2(NO3)2

UO2(ClO4)2

UO2(Tf)2

UO2(Tf2N)2

UO2(NO3)2.6H2OUO2(ClO4)2.6H2OUO2(CF3SO3)2

UO2(Tf2N)2

UO2(Tf2N)2

UO2(CF3SO3)2

UO2(ClO4)2.6H2O

UO2(NO3)2.6H2O

Salt is dissolved but may not be dissociated (≠ water)

U L3 edge @ ROBL (ESRF)

3.5 6 8.5 11 13.5 16

k3.c

hi(

k)

k (Å-1) 0 1 2 3 4

FT m

ag.

R + Δ (Å)

∼5 O @ 2.43 Å + 2.7 S @ 3.62 Å [UO2(Tf2N)5-6]

∼ 4.5 O @ 2.42 Å

∼ 4.4 O @ 2.42 Å

∼ 5 O @ 2.49 Å + 2 N @ 2.92 Å [UO2(NO3)2] + (1 or 2) Tf2N

Gaillard et al., Inorg Chem, 2007, 46, 4815.

“Simple” complexation reactions in IL

- In IL, possibility to get rid of counter-ions:

UO2(Tf2N)2 + nC4mimNO3 → [UO2(NO3)n]2-n + nC4mimTf2N

0 < R = [NO3-]/[UO2

2+] < 5

UO2(Tf2N)2 + C4mimNO3 in C4mimTf2N

U-Oeq @ 2.48 ÅU-N @ 2.92 Å

U L3 edge @ ROBL (ESRF)

3 5 7 9 11 13 15

k3.c

hi(

k)

k (Å-1)0 1 2 3 4 5

FT m

ag.

R+Δ (Å)

R = 0

R = 1

R = 2R = 3

Total complexation, up to the formation of [UO2(NO3)3]-

Same structural parameters as in organic solvents

Georg et al., J. Phys.Chem B, 2010,114,4276.Gaillard et al. Inor Chem, 2010, 49, 6484

UO2(NO3)2: 2 bidentate NO3Mixture of 1:1, 1:2 and 1:3 cpx2 UO2(NO3)2 → UO2(NO3)+ + UO2(NO3)3

-

UO2(NO3)+ : 1 bidentate NO3-

UO2(NO3)3-: 3 bidentate NO3

R = 600

“Simple” complexation reactions in IL (2)

- an IL can be solvent AND reactant

UO2(Tf2N)2 IN C4mimNO3 and, even better, UO2(NO3)2 IN C4mimNO3

-3

-1

1

3

5

3 5 7 9 11 13 15

k3.c

hi(

k)

2

4

6

8

10

FT m

ag

[UO2(NO3)3]-

UO2(NO3)2

[UO2(NO3)]+

UO2(NO3)2 in BMINO3

Gaillard et al., Dalton Trans., submitted

Same structural parameters as in solid state

∼ 4 NO3- complexed to U(VI),

2 bidentate and 2 mono-dentate

→ Formation of UO2(NO3)4]2-

-5

-3

k (Å-1)0

0 1 2 3 4 5R + Δ (Å)

U L3 edge @ ROBL (ESRF)

Competition between strong ligands (with the help of MD)

UO2(TfO)2 + 4 C4mimCl in C4mimTf2N

→ Chlorides are strong ligands

U(VI) + 2 strong ligands: chlorides + nitrates

UO2(NO3)2 + 4 C4mimCl in C4mimTf2N

UO2(NO3)2 + 2 C4mimCl in C4mimTf2N0

10

20

370 420 470 520

ε(m

ol-1

. cm

-1)

λ (nm)

0

10

20

370 420 470 520

ε(m

ol-1

. cm

-1)

λ (nm)

0

10

20

370 420 470 520

ε(m

ol-1

. cm

-1)

λ (nm)

-6

-1

4

9

14

3 8 13

k3.c

hi(

k)

k (Å-1) 0 1 2 3 4

FT m

ag.

R + Δ (Å)

U L3 edge @ ROBL (ESRF)

-6

-1

4

9

14

3 8 13

k3.c

hi(

k)

k (Å-1) 0 1 2 3 4

FT m

ag.

R + Δ (Å)

-6

-1

4

9

14

3 8 13

k3.c

hi(

k)

k (Å-1) 0 1 2 3 4

FT m

ag.

R + Δ (Å)

∼ 4 Cl @ 2.69 Å ⇒ 100 % of [UO2Cl4]2�

∼ 4 Cl @ 2.70 Å ⇒ [UO2Cl4]2' + some [UO2Cl3(NO3)]

2�

∼ 1 Cl @ 2.67 Å + 2 bid. NO3-⇒ [UO2Cl(NO3)2]

�

Ion competition can lead to the formation of mixed complexes

May IL anions interfere in complexation reactions?

Dissolution of Eu(TfO)3 in various IL (≠ anions, same cation) and addition of 6xCl-

Eu/Cl complexation?

0

2

4

6

8

10

12

0 1 2 3 4

FT m

ag.

R + Δ (Å)

C4mim-TfO

0

1

2

3

4

5

6

7

8

9

0 1 2 3 4

FT m

ag.

R + Δ (Å)

C4mim-BF4

0

2

4

6

8

10

12

14

0 1 2 3 4

FT m

ag.

R + Δ (Å)

C4mim-Tf2NEu-ClEu-O

[EuCl3-4]

R + Δ (Å)

[EuCl2-3]

R + Δ (Å)

0

2

4

6

8

10

12

0 1 2 3 4

FT m

ag.

R + Δ (Å)

C4mim-PF6

No Cl complexation but fluorides!

Eu-L3 edge @ XAS-BL (ANKA)

R + Δ (Å)

[EuCl63-]: total complexation

Gaillard et al., Inorg Chem, 2005, 44, 8355

The species formed are the result of competition between all components of the solution, including the solvent→ Formation of mixed complexes

⇔ PF6- (and possibly BF4

-) decomposition into F-

Comparison Ln(III) and An(III)

Eu(III) + N3- in C4mim-Tf2N

• Eu(OTf)3 or Eu(ClO4)3; C = 10-2 M;

• [N3-] = 10-5 M to 5x10-1 M

• Cm(ClO4)3; C = 1.2x10-7 M;

• [N3-] = 2x10-8 M to 10-5 M

Cm(III) + N3- in C4mim-Tf2N

→ Complexation is fast (instantaneous) but not total

→ Complexation is slow (≈ 7 days)

1500

2000

2500

3000

Inte

nsi

ty

time elapsed

30000

40000

50000

60000

70000

Inte

nsi

ty

[N3-] ↑

Eu and Cm solvate similarly in IL→ concentration effect?

TRLFS, INE (FZK)

0

500

1000

1500

575 585 595 605 615

Inte

nsi

ty

λ (nm)TRLFS, IPHC

0

10000

20000

30000

570 590 610 630

Inte

nsi

ty

λ(nm)

Am(III) + N3- in C4mim-Tf2N

Comparison Ln(III) and An(III)

Eu(III) + N3- in C4mim-Tf2N Cm(III) + N3

- in C4mim-Tf2N

11 O @ 2.42 Å + ~ 4 Cl/S @ 3.60 Å

• Am(ClO4)3; C = 10-3 M; [N3-] = 10-2 M;

• Eu(OTf)3 or Eu(ClO4)3; C = 10-2 M;

• [N3-] = 10-5 M to 5x10-1 M

• Cm(ClO4)3; C = 1.2x10-7 M;

• [N3-] = 2x10-8 M to 10-5 M

→ Complexation is fast (instantaneous) but not total

→ Complexation is slow (≈ 7 days)

5Am(ClO4)3 in C4mimTf2N

→ Complexation is slow and non-total after 7 days

Am-L3 edge @ INE-BL (ANKA)

11 O @ 2.42 Å + ~ 4 Cl/S @ 3.60 Å

→ Am solvatation in IL

9 O @ 2.42 Å; no 2nd shell

→ destruction of Am solvatation sphere

11 O @ 2.40 Å + MS from [Am(N3)x]3-x

→ azide complexation to Am

� In both cases: formation of mixed complexes postulated� ≠ complexation kinetics can not be explained by concentration effects

⇒ ≠ reactivity of An(III) and Ln(III) in IL

0

1

2

3

4

0 1 2 3 4 5

FT m

ag.

R +Δ (Å)

Am(ClO4)3 in C4mimTf2N

Am(ClO4)3 + N3 ; fresh

Am(ClO4)3 + N3 ; 1 week

S. Stumpf et al., Inorg. Chem., 2008, 47, 4618

Conclusion

- The final coordination sphere of An/Ln depends on competition phenomena, in which the IL ions and Ln/An counter-anions take part

- IL can be solvent + reactant: formation of unusual species in liquid state like [(UO2(NO3)4]2-

- Impurities may have a drastic effect (cf. example of fluorides, but also water – not shown here)

- Strength of Ln/An ligands in IL:Tf2N- < TfO- < ClO4

- < Cl- ≈< NO3- < F-

- Evidence of Ln/An(III) different kinetics of complexation- Evidence of Ln/An(III) different kinetics of complexation

Danke schön to all persons that have contributed more or less to this work: on ROBL, at INE, at ANKA.