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5f-element chemistry revealed by actinide ions in the gas phase

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.

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5f-element chemistry revealed by actinide ions in the gas phase

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  1. 5f-element chemistry revealed by actinide ions in the gas phase John K. Gibson Chemical Sciences Division Lawrence Berkeley National Laboratory

  2. Outline • Experimental method / actinides • Molecular thermodynamics • Exotic oxidation states • Reaction mechanisms • Metal-metal bonding

  3. Experimental Approach: Gas-phase reactions by Mass Spectrometry

  4. Bimolecular ion-molecule reactions I+/- + XY→ IX+/- + Y PuO+ Pa2+ UPt+ U2O6- … O2C3H8CH3OH CD3OH …

  5. Fourier Transform Ion Cyclotron Resonance Mass Spectrometry AnnL+/- by laser desorption ionization of actinide-containing solid targets

  6. Pu+ + O2 2 x 10-7 Torr O2 200 ms PuO+ PuO+ + O2→ PuO2+ + O Pu+ + O2→ PuO+ + O Pu+ PuO2+ Pseudo first-order kinetics: d[Pu+]/dt = k[O2][Pu+] = k[Pu+]

  7. d-block transition elements 3dn 4dn La 5dn Th Ac 6dn f-block transition elements Lanthanides: localized 4f n Actinides: bonding 5f n 5f electrons in molecular bonding ?

  8. Th6d2 7s2 6d transition metal Pa5f2 6d 7s2 f-bonding (?) U5f3 6d 7s2 Np5f4 6d 7s2 Pu5f6 7s2 Am5f7 7s2 f-localized Cm5f7 6d 7s2 Bk5f9 7s2 Cf 5f10 7s2 Es 5f11 7s2

  9. Oxidation States High Oxidation States / 5f → 6d Promotion Direct 5f participation in chemistry

  10. Experimental Challenges / Hazards 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 Need good theory!

  11. Gas-phase actinide chemistry: ▪ Fundamental science ▪ Basis for development & validation of theoretical approaches

  12. Molecular thermodynamics

  13. Thermodynamics of PuO2+ PuO+ + O2 → PuO2+ + O D[OPu+-O] ≥ 498 kJ/mol D[O-O] If a reaction occurs at low energy then ∆H ≤ 0 ∆S undefined, zero?

  14. Conflict between experiments: PuO2+ • D[OPu+-O] = • D[OPu-O] + IE[PuO] – IE[PuO2] ? +636 -970 +598 = 264 kJ /mol* (<<498 kJ/mol) *Electron impact of PuO2(g): F. Capone, et al., J. Phys. Chem. A1999, 103, 10899

  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 X 6.93 eV 7.12 eV

  16. D[OPu+-O] = • D[OPu-O] + IE[PuO] – IE[PuO2] X -970 +598 +636 672 X = 264 kJ /mol 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

  18. The Bare Actinyls {O=An=O}2+ AnO2+ + N2O → AnO22+ + N2 UO22+ NpO22+ PuO22+

  19. Actinyl Thermodynamics AnO22+ + X → AnO2+ + X+ IE[AnO2+] > IE[X] + E* Barrier from AnO2+ / X+ repulsion ΔHf[AnO22+] = ΔHf[AnO2+] + IE[AnO2+]

  20. Actinyl Thermodynamics ΔHhyd[AnO22+] (kJ mol-1) AnO22+(g) AnO22+(aq) Calorimetry This Work

  21. Actinyl Hydration / Experiment ↔ DFT ΔHhyd[AnO22+] ≈ -1660 kJ mol-1* UO22+, NpO22+, PuO22+ J. Phys. Chem. A 109 (2005) 2768 ΔHhyd[UO22+ ] = -1676 kJ mol-1 Moskaleva et al. Inorganic Chemistry 43 (2004) 4080 ΔHhyd[AnO22+] = -1820 ± 10 kJ mol-1 Shamov & Schreckenbach J. Phys. Chem. A 109 (2005) 10961 *Experiment: -1780 with “revised” ΔHhyd[H+(aq)]

  22. Exotic oxidation states

  23. 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” ?

  24. “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

  25. Protactinyl: LC-RECP SCF Calculation IE[PaO2+] = 16.61 eV PaO2+PaO22+ PaOPaO s 2.11 3.67 2.09 3.71 p5.91 8.75 5.75 8.23 d 1.66 0.04 1.64 0.05 f 1.86 ----- 1.53 ----- totals 11.54 12.46 11.01 11.99 Pa5.5 PaV Pitzer, Mrozik & Bursten

  26. Why not PaO22+(aq)? {O-An-O}2+→ An2+ + 2O ΔH / kJ mol-1 UO22+ > PaO22+ ≥ NpO22+ > PuO22+ > AmO22+ 1250 1110 1030 830 600 PaO22+(aq) + ½H2O(l) → PaVO(OH)2+(aq) + ¼O2(g) ΔG ≈ -110 kJ mol-1

  27. AmO22+(g) ? Is bare americyl stable? AmO22+Am+ + O2+ ΔHdissociation ≈ 1 ± 1 eV ?

  28. Reaction mechanisms • 5f-electron bonding • “Interfacial” chemistry

  29. Carbon-Hydrogen Bond Activation: 5f electrons in Organoactinide Chemistry • Do 5f electrons participate in molecular bond activation? • Is 5f electron promotion required: 5f n-1 7s → 5f n-2 6d7s ? 5fxyz

  30. Hydrocarbon Activation by An+Role of the 5f electrons in organoactinide chemistry Fast H2-elimination Slow An+- insertion

  31. An+[Ground] → An+[5fn-26d7s] C-An+-H requires 5fn-26d7s configuration Inert Intermediate Reactive ? ? ? Beyond Np+, the 5f electrons do not participate in C-H bond activation

  32. 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 ?

  33. Dehydrogenation of Ethylene: MO+ + C2H4→ MOC2H2+ + H2 TaO+ 0.31 ThO+ <0.001 PaO+ 0.17 UO+ <0.001 NpO+ <0.001 • • • Organometallics 26 (2007) 3947-3956

  34. Electronic structures of MO+ Unreactive MO+ {Th(7s)O}+ {U(5f3)O}+ Reactive MO+ {Ta(5d1 6s1)O}+ {Pa(5fx 6dy 7sz)O}+ x + y + z = 2 SOCISD/RECP: {Pa(5f16d1)O+} Pitzer, Mrozik & Bursten

  35. Electronic configurations of PaO+

  36. PaO+ + H2C=CH2 ↓ H O H Pa+ C=C H H ↓ -H2 OPa+-{HC≡CH} High reactivity of PaO+ indicates chemically active 5f electron(s)

  37. 5f-electrons in organoactinides C-H activation by: Pa+(5f26d7s) Pa2+(5f26d) Pa(5f6d)O+ 5f-participation in σ-type bonding in “C-Pa-H”

  38. Gas-Phase Ion Reaction Mechanisms: “Interfacial” Chemistry CH3OH(g) CH3 O CH3 O CH3 O CH3 O CH3 O CH3 O U U U U U U UO2(s) Lloyd, Manner & Paffett, Surface Science1999, 423, 265-275.

  39. Uranium Oxide Negative Ions: Molecules & Clusters “(NH4)+2UO42-UO3(s)” ↓ hν UVO3- UVIO3(OH)- UVIIO4- U2V/VIO6- U3VO8- U3V/VIO9-

  40. Molecular Anion Reactions with Methanol UVO3- + CH3OH → UIIIO(OH)2- + CH2O k/kCOL = 21% UVIIO4- + CH3OH → UVO2(OH)2- + CH2O k/kCOL = 4% +N2O -N2

  41. UVO3- UVIIO4- + 2H / -CH2O ↓ 21% + 2H / -CH2O ↓ 4% X UIIIO(OH)2- UVO2(OH)2- + CH2 / -H2O ↓ 17% + OCH2 / -H2↓ 21% UVO2(OH)(OCH3)- + CH2 / -H2O ↓ 18% OCH3 - O=U=O ? UVO2(OCH3)2- OCH3

  42. Preliminary Theoretical Results / UO3H2- M. Michelini & N. Russo, U. Calabria PW91/ZORA B3LYP/SDD UO2(OH)H- X UO(OH)2- H I O=U=O I OH

  43. Structures & Mechanisms from Isotopic Labeling UO3- + CD3OH → UO3HD- (+ CD2O) UO3HD- + CD3OH → UO4HCD3- (+ HD) UO4HCD3- + CD3OH → UO4C2D6- (+ H2O) No Isotopic Scrambling

  44. UO3HD-+CD3O-H→ UO4HCD3- (+ HD) O O-H - O-U-O O=U O-D H D HH & HD

  45. UO3HD-+CD3O-H→ UO4HCD3- (+ HD) H O D O O=U=O O=U=O H D HH HD

  46. Cluster Anion Reactions with Methanol UV/VI2O6- + OCH3, H ↓ 11% UV/VI2O5(OCH3)(OH)- + CH2 / -H2O ↓ 27% Same sequence for UV3O8- & UV/VI3O9- UV/VI2O5(OCH3)2- • • • ↓ UV/VI2O3(OCH3)6-

  47. Cluster Anion Reactions with Methanol UV,VI2O6- + 6CD3OH → UV,VI2O3(OCD3)6- + 3H2O - O D3CO OCD3 ? O OCD3 U U D3CO O OCD3 D3CO Analogous to methoxidation of UOx(s) surfaces

  48. Metal-metal bonding

  49. Actinide – Transition Metal Covalent Bonding J. M. Ritchey, et al., J. Am. Chem. Soc. 1985, 107, 501-503.

  50. Bimetallic Ions by LDI of Actinide-Transition Metal Alloys ThPt+ PaPt+ UPt+ NpPt+ PuPt+ AmPt+ CmPt+ UIr+ UAu+ 20% U / 80% Au Nd-YAG 1064 nm

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