5f-element chemistry revealed by actinide ions in the gas phase John K. Gibson Chemical Sciences...
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Transcript of 5f-element chemistry revealed by actinide ions in the gas phase John K. Gibson Chemical Sciences...
5f-element chemistry revealed
by actinide ions in the gas phase
John K. Gibson
Chemical Sciences Division
Lawrence Berkeley National Laboratory
Outline
• Experimental method / actinides
• Molecular thermodynamics
• Exotic oxidation states
• Reaction mechanisms
• Metal-metal bonding
Experimental Approach:
Gas-phase reactions byMass Spectrometry
Bimolecular ion-molecule reactions
I+/- + XY → IX+/- + Y
PuO+ Pa2+ UPt+ U2O6- …
O2 C3H8 CH3OH CD3OH …
Fourier Transform Ion CyclotronResonance Mass Spectrometry
AnnL+/- by laser desorption ionizationof actinide-containing solid targets
Pu+ + O2
2 x 10-7 Torr O2
200 ms
Pu+
PuO+
PuO2+
Pu+ + O2 → PuO+ + O PuO+ + O2 → PuO2+ + O
Pseudo first-order kinetics:d[Pu+]/dt = k[O2][Pu+] = k[Pu+]
5dn
6dn
Actinides:bonding 5f n
3dn
4dn
Lanthanides:localized 4f n
d-block transition elements
f-block transition elements
La
AcTh
5f electrons in molecular bonding ?
Th 6d2 7s2 6d transition metalPa 5f2 6d 7s2 f-bonding (?)U 5f3 6d 7s2
Np 5f4 6d 7s2
Pu 5f6 7s2
Am 5f7 7s2 f-localizedCm 5f7 6d 7s2
Bk 5f9 7s2
Cf 5f10 7s2
Es 5f11 7s2
7
6
5
4
3
2
Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr
Oxidation States
High Oxidation States / 5f → 6d PromotionDirect 5f participation in chemistry
Alpha decay (4-7 MeV)
U-238 10 / s.mg
Np-237 104 / s.mg
Pu-242 105 / s.mg
Am-243 107 / s.mg
Es-253 109 / s.µg
Experimental Challenges / Hazards
Need good theory!
Gas-phase actinide chemistry:
▪ Fundamental science
▪ Basis for development & validationof theoretical approaches
Molecular thermodynamics
Thermodynamics of PuO2+
PuO+ + O2 → PuO2+ + O
D[OPu+-O] ≥ 498 kJ/mol
If a reaction occurs at low energythen ∆H ≤ 0
∆S undefined, zero?
D[O-O]
D[OPu+-O] =
D[OPu-O] + IE[PuO] – IE[PuO2]+598 +636 -970
= 264 kJ /mol* (<<498 kJ/mol)
*Electron impact of PuO2(g):
F. Capone, et al., J. Phys. Chem. A 1999, 103, 10899
Conflict between experiments: PuO2+
?
15
IE[PuO2] from Electron-Transfer
PuO2+ + DMPT → PuO2 + DMPT +
PuO2+ + DMA → PuO2 + DMA+
No kinetic barrier to electron transfer:
IE[DMPT] ≤ IE[PuO2] ≤ IE[DMA]
IE[PuO2] = 7.03 ± 0.12 eV
vs. IE[PuO2] = 10.1 ± 0.1 eV from Electron Impact
6.93 eV 7.12 eV
X
D[OPu+-O] =
D[OPu-O] + IE[PuO] – IE[PuO2]
+598 +636 -970
= 264 kJ /mol
X
X
672
562 (≥ 498 kJ/mol)
17
IE[PuO2]
New Experimental: 7.02 ± 0.12 eV
Preliminary Theoretical Results
L. Gagliardi, U. Geneva
CASPT2: 6.5 – 7 eV
The Bare Actinyls{O=An=O}2+
AnO2+ + N2O → AnO22+ + N2
UO22+ NpO2
2+ PuO22+
Actinyl Thermodynamics
AnO22+ + X → AnO2
+ + X+
IE[AnO2+] > IE[X] + E*
Barrier from AnO2+ / X+ repulsion
ΔHf[AnO22+] = ΔHf[AnO2
+] + IE[AnO2+]
Actinyl Thermodynamics
ΔHf[AnO22+(g)] ΔHf[AnO2
2+(aq)] ΔHhyd[AnO22+]
UO22+ 1524 -1019 -1665
NpO22+ 1671 -861 -1654
PuO22+ 1727 -822 -1671
ΔHhyd[AnO22+]
AnO22+(g)
AnO22+(aq)
(kJ mol-1)
This Work Calorimetry
Actinyl Hydration / Experiment ↔ DFT
ΔHhyd[AnO22+] ≈ -1660 kJ mol-1*
UO22+, NpO2
2+, PuO22+
ΔHhyd[UO22+ ] = -1676 kJ mol-1
Moskaleva et al. Inorganic Chemistry 43 (2004) 4080
J. Phys. Chem. A 109 (2005) 2768
ΔHhyd[AnO22+] = -1820 ± 10 kJ mol-1
Shamov & Schreckenbach J. Phys. Chem. A 109 (2005) 10961
*Experiment: -1780 with “revised” ΔHhyd[H+(aq)]
Exotic oxidation states
Actinides in High Oxidation States
AnO+ + C2H4O → An(V)O2+ + C2H4
D[OAn+-O] ≥ 354 kJ mol-1
ThO2+ PaO2
+ UO2+
NpO2+ PuO2
+ AmO2+
Electronic structures ?
“6p hole” ?
“Protactinyl”
PaO2+ + N2O → {O-Pa-O}2+ + N2
D[OPa2+-O] ≥ 167 kJ mol-1
IE[PaO2+] = 16.6 ± 0.4 eV
J. Phys. Chem. A 110 (2006) 5751
Protactinyl: LC-RECP SCF Calculation
PaO2+ PaO2
2+
Pa O Pa Os 2.11 3.67 2.09 3.71p 5.91 8.75 5.75 8.23d 1.66 0.04 1.64 0.05
f 1.86 ----- 1.53 -----
totals 11.54 12.46 11.01 11.99
IE[PaO2+] = 16.61 eV
Pa5.5PaV
Pitzer, Mrozik & Bursten
Why not PaO22+(aq)?
{O-An-O}2+ → An2+ + 2O ΔH / kJ mol-1
UO22+ > PaO2
2+ ≥ NpO22+ > PuO2
2+ > AmO22+
1250 1110 1030 830 600
PaO22+(aq) + ½H2O(l) → PaVO(OH)2+(aq) + ¼O2(g)
ΔG ≈ -110 kJ mol-1
AmO22+ (g) ?
Is bare americyl stable?
AmO22+ Am+ + O2
+
ΔHdissociation ≈ 1 ± 1 eV
?
Reaction mechanisms
• 5f-electron bonding
• “Interfacial” chemistry
• Do 5f electrons participate in molecular bond activation?
• Is 5f electron promotion required: 5f n-1 7s → 5f n-2 6d 7s ?
5fxyz
Carbon-Hydrogen Bond Activation:
5f electrons in Organoactinide Chemistry
Hydrocarbon Activation by An+
Role of the 5f electrons in organoactinide chemistry
SlowAn+- insertion
FastH2-elimination
0
50
100
150
200
250
300
Th Pa U Np Pu Am Cm Bk Cf
Pro
mo
tio
n E
ner
gy
(kJ/
mo
l)
C-An+-Hrequires
5fn-26d7sconfiguration
Reactive
Inert
Intermediate
Beyond Np+, the 5f electrons do notparticipate in C-H bond activation
An+[Ground] → An+[5fn-26d7s]
? ? ?
Hydrocarbon Activation by AnO+
The role of the 5f electrons—early actinides
Employ An valence electrons in An+=O bonds:Do 5f electrons at metal center oxidatively insert ?
MO+ + C2H4 → MOC2H2+ + H2
Dehydrogenation of Ethylene:
TaO+ 0.31
ThO+ <0.001
PaO+ 0.17
UO+ <0.001
NpO+ <0.001 • • •
Organometallics 26 (2007) 3947-3956
Electronic structures of MO+
{Th(7s)O}+ {U(5f3)O}+
Unreactive MO+
Reactive MO+
{Pa(5fx 6dy 7sz)O}+{Ta(5d1 6s1)O}+
SOCISD/RECP: {Pa(5f16d1)O+}
x + y + z = 2
Pitzer, Mrozik & Bursten
Electronic configurations of PaO+
Excitation Energy (eV)0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80
Orb
ital O
ccup
atio
n
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
5f Orbitals6d Orbitals7s Orbital
High reactivity of PaO+ indicateschemically active 5f electron(s)
PaO+ + H2C=CH2
↓
OPa+-{HC≡CH}
↓
C=CHH
HH
Pa+O
-H2
5f-electrons in organoactinides
C-H activation by:
Pa+(5f26d7s)
Pa2+(5f26d)
Pa(5f6d)O+
5f-participation in σ-typebonding in “C-Pa-H”
UO2(s)
U UU U UU
CH3
O
CH3
O
CH3
O
CH3
O
CH3
O
CH3
O
CH3OH(g)
Gas-Phase Ion Reaction Mechanisms:“Interfacial” Chemistry
Lloyd, Manner & Paffett, Surface Science 1999, 423, 265-275.
“(NH4)+2UO4
2-UO3(s)”
↓ hν
UVO3- UVIO3(OH)- UVIIO4
-
U2V/VIO6
- U3VO8
- U3V/VIO9
-
Uranium Oxide Negative Ions:Molecules & Clusters
UVO3- + CH3OH → UIIIO(OH)2
- + CH2O
k/kCOL = 21%
UVIIO4- + CH3OH → UVO2(OH)2
- + CH2O
k/kCOL = 4%
Molecular Anion Reactions with Methanol
+N2O -N2
+ 2H / -CH2O ↓ 21%
+ OCH2 / -H2 ↓ 21%
+ 2H / -CH2O ↓ 4%
+ CH2 / -H2O ↓ 17%
+ CH2 / -H2O ↓ 18%
UVO3- UVIIO4
-
UIIIO(OH)2- UVO2(OH)2
-
UVO2(OH)(OCH3)-
UVO2(OCH3)2- O=U=O
OCH3
OCH3
-
?
X
Preliminary Theoretical Results / UO3H2-
M. Michelini & N. Russo, U. Calabria
PW91/ZORA B3LYP/SDD
UO(OH)2-
UO2(OH)H-
H I
O=U=O I
OH
X
Structures & Mechanismsfrom Isotopic Labeling
UO3- + CD3OH → UO3HD- (+ CD2O)
UO3HD- + CD3OH → UO4HCD3- (+ HD)
UO4HCD3- + CD3OH → UO4C2D6
- (+ H2O)
No Isotopic Scrambling
O=U
UO3HD- + CD3O-H → UO4HCD3- (+ HD)
O-H
O-D
HH & HD
O-U-OO-
H D
UO3HD- + CD3O-H → UO4HCD3- (+ HD)
O=U=O
D
O
D
HH
H
O
O=U=O
H
HD
Cluster Anion Reactions with Methanol
UV/VI2O6
-
+ OCH3, H ↓ 11%
UV/VI2O5(OCH3)(OH)-
+ CH2 / -H2O ↓ 27%
UV/VI2O5(OCH3)2
-
•••
UV/VI2O3(OCH3)6
-
↓
Samesequence
for
UV3O8
-
&
UV/VI3O9
-
Cluster Anion Reactions with Methanol
UV,VI2O6
- + 6CD3OH → UV,VI2O3(OCD3)6
- + 3H2O
U U
O
O
O
OCD3
OCD3
OCD3
D3CO
D3CO
D3CO
-
Analogous to methoxidation of UOx(s) surfaces
?
Metal-metal bonding
Actinide – Transition MetalCovalent Bonding
J. M. Ritchey, et al., J. Am. Chem. Soc. 1985, 107, 501-503.
Bimetallic Ions by LDI ofActinide-Transition Metal Alloys
ThPt+
PaPt+
UPt+
NpPt+
PuPt+
AmPt+
CmPt+
UIr+
UAu+
20% U / 80% AuNd-YAG 1064 nm
P. Pyykkö et al., Chem. Phys. Lett. 381 (2003) 45
“Autogenic Isolobality”
2Au (5d106s1) ~ 2H (1s1)
3Pt (5d96s1) ~ 3O (2s22p4)
4Ir (5d76s2) ~ 4N (2s22p3)
Actinide-Transition Metal Bonding:“Autogenic Isolobality”
Gagliardi & Pyykkö, Angewandte Chem. 43 (2004) 1573
{U-Au}+ ↔ {U-H}+
{U=Pt}+ ↔ {U=O}+
{U≡Ir}+ ↔ {U≡N}+
U+ UO+ 0.34 NR <0.001
Ir+ IrCH2+ 0.21 IrC2H4
+ 0.23
Pt+ PtCH2+ 0.16 PtC2H4
+ 0.24
Au+ AuCH2+ 0.11 AuC2H4
+ 0.19
UIr+ OUIr+ 0.24 NR <0.001
UPt+ OUPt+ 0.21 NR <0.001
UAu+ OUAu+ 0.28 NR <0.001
Reactivities of UM5d+ Bimetallic Ions
C2H4O C2H6
Reactivities of UM5d+
{AuI-UII}+ {PtII=UIII}+ {IrIII≡UIV}+
• Reactivities of M5d are “shut off”, consistent with covalent bonding & bonding saturation: AuI; PtII; IrIII
• Reactivities of the UM5d+ are similar
to bare U+; oxidation consistent with oxidation states up to U(VI) in {Ir≡U=O}+
{U=O}2+ + N2O → {O=U=O}2+ + N2
{U≡N}+ + O2 → {O=U≡N}+ + O
Pseudoactinyls
1.65 Å
1.72 Å 1.63 Å
Pyykkö et al., 1994
“Metalloactinyls”:{OUIr}+ as an Analogue to Uranyl
{U≡Ir}+ + N2O → {O=U≡Ir}+ + N2
1.75 Å 2.15 Å
Gagliardi & Pyykkö, 2004
Gas-Phase Actinide Ion Chemistry
A probe of fundamental aspectsof actinide chemistry:
molecular thermodynamics to “surface chemistry” of clusters.
Theory ↔ Experiment
Experiment
Instituto Tecnológico e Nuclear, Portugal
J. Marçalo, A. Pires de Matos, M. Santos
Oak Ridge National Laboratory, USA
R.G. Haire
Theory
Ohio State University, USA
R.M. Pitzer, M.K. Mrozik, R. Tyagi
University of Tennessee, USA
B.E. Bursten
University of Calabria, Italy
N. Russo, M. Michelini
University of Geneva, Switzerland
L. Gagliardi
Research at Lawrence Berkeley National Lab supported byOffice of Basic Energy Sciences, U.S. Department of Energy