1 / 59

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.

truly
Download Presentation

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

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related