Emerging trends in NMR of materials

Transcription

1 Emerging trends in NMR of materials Marek Pruski U.S. DOE Ames Laboratory, Ames, Iowa 500, U.S.A Department of Chemistry, Iowa State University, Ames, Iowa 500, U.S.A. UHF Workshop, Bethesda, November, 05

2 Research needs in materials science Understanding the structure- property rela:ons in novel materials is an unanswered scien:fic challenge, which prevents ra:onal design. A few examples:! heterogeneous catalysts: supports, cataly8c sites, reac8on mechanisms! energy related materials: ba<eries, fuel cells, hydrogen storage, thermoelectrics, photovoltaics,! construc8on materials: cements, polymers, composites! glasses and ceramics! semiconductors, ion- conduc8ng solids, and dielectric materials! materials for environmental remedia8on and CO sequestra8on! biomaterials! pharmaceu8cals (more examples are given in Task Force Summaries, p. 5-6)

3 Solid- state NMR SS- NMR spectroscopy has an unparalleled ability to provide atomic- level characteriza:on of materials:! most elements have NMR- ac8ve isotopes! nuclear spins are excellent, site- dependent reporters of local structure and dynamic processes Challenges:! intrinsically low sensi8vity of NMR! low resolu8on; homogeneous and inhomogeneous line broadening in solids Transforma:onal role of ultrahigh field in SS- NMR:! ultrafast MAS; indirect detec8on! low- gamma nuclei! half- integer quadrupolar nuclei! high- field DNP 3

4 Characteriza:on by SS- NMR D MAS spectra of catalytic surface; 4. T, MAS at 40 khz AL-MSN Si 3 H H H3 OH/H O H 3 C 9 Si C C3 C Q3 MeO CTAB T T3 Q Q D correlation spectra of the same system H3 C C3 C H H CTAB d H ppm MeO 0 H-H H- 3 C H-9Si H 3 4 H3 5 H d C ppm Q4 T3 Q3 T H H H3 J. Trebosc, et al., J. Am. Chem. Soc., 005, 7, ; J. Am. Chem. Soc., 005, 7,

5 Emerging technique: ultrafast MAS New probes (e.g. ultrafast MAS): new pulse sequences/theory; improved resolution & sensitivity! MAS rate: 45 khz! volume: ~9 μl! introduced: ~005! MAS rate: 00+ khz! volume: ~0.3 μl! introduced: ~0 Transforma:onal role of ultrafast MAS in SS- NMR:! improved H resolu8on! be<er sensi8vity/spin (Δν~(ν MAS ) - )! higher RF fields! indirect detec8on! improved decoupling/recoupling! sideband- free spectra! dipolar trunca8on Need higher magnetic field!!! 5

6 H resolu:on under ultrafast MAS L-histidine HCl H O H MAS at 4. T 00 khz 80 khz 60 khz 0 khz 40 khz 0 khz ! H resolu8on and SNR are greatly enhanced by fast MAS! CRAMPS- like resolu8on approached at 00 khz Y. Nishiyama, JEOL Resonance. 6

7 H resolu:on under ultrafast MAS L-histidine HCl H O H INADEQUATE at 4. T 0 khz 0 khz 60 khz 80 khz 90 khz 00 khz! H resolu8on and SNR are greatly enhanced by fast MAS Y. Nishiyama, JEOL Resonance. 7

8 H- H correla:ons under MAS at 00 khz Ultrafast MAS at 00 khz: improved resolu:on in D H- H NMR! Host- guest interac8on in corrole/toluene system D MAS 40 khz 60 khz 80 khz A A 00 khz B B slice δ H (DQ, ppm) H- H DQMAS 00 khz A A-B B δ H (ppm) H- H spin diffusion 60 khz δ H (SQ, ppm) δ H (ppm) Polymers, supramolecular systems, catalysts, T. Kobayashi, et al., Angew. Chem. Int. Ed., 03, 5, 408. S.P. Brown, Macromol. Rapid. Commun. 009, 30,

9 Indirect detec:on of low- γ nuclei Tradi:onal SSNMR approach: direct detec:on of low- γ nuclei (e.g. 3 C, 5 N)! H homonuclear RF decoupling! low sensitivity Indirect detec:on of low-γ nuclei! H decoupling by fast MAS! high sensitivity H Low-γ H Low-γ t : H t : X t : X t : H S/N gain: ( S / N) ( S / N) ID DD δν α δν X H / γ γ H X 3/ For 5 N: γ H γ N 3 / = 3 time performance improves by ~0 3! 9

10 H- 3 C HETCOR under fast MAS: cataly:c surface X H 3 C, 5 N Y X Decoupling Y X Y Recoupling Y,Y CP or INEPT ϕ, ϕ+π SPINAL-64 Through space correlations: Ishii, Y.; Tycko, R. JMR, 000, 4, 99; Wiench, J.W. et al. JACS 007, 9, 077; Zhou D.G. et al., JACS 007, 9, 79 Through-bond correlations: Elena, B. et al. JACS, 005, 7, 796; Mao, K.; Pruski, M. JMR, 009, 0, 65; τ CP t τ RR τ CP t (a) C F C3 Direct 5 h CTAB C CTAB H H3 (b) F H Indirect 5 min H3 H CTAB C CTAB C3 40 khz MAS AL-MSN Si Si 3 H 50 C F F! H- H homonuclear RF decoupling INEPT 0

11 H- 3 C HETCOR under MAS at 00 khz 0 3 C Chemical Shift / ppm MP- MSN MP c b a a c b 7 h H Chemical Shift / ppm 3 C Chemical Shift / ppm H Chemical Shift / ppm! Excellent sensi8vity and resolu8on; all resonances detected! H- H interac8ons are suppressed during CP; one- bond selec8vity (dipolar trunca8on)! HMQC possible when T > 0 ms T. Kobayashi, et al., Angew. Chem. Int. Ed., 03, 5, 408.

12 HSQC of f- MLF- OH under natural abundance at 4. T (A) 00 khz MAS (0.75- mm); H detec:on; 5 h (B) khz MAS (.6- mm); H detec:on; 0 h (C) khz MAS (.6- mm); 3 C detec:on; PMLG during t, 0 h! Sensi8vity/scan at 00 khz close to that of.6- mm probe (>50% in terms of SNR), in spite of 0x smaller volume! Resolu8on in (A) similar to PMLG (C) Y. Nishiyama, T. Kobayashi, et al., SSNMR, 66-67, 56-6 (05)

13 3 C CPMAS NMR of Argonne Premium Coals at low and high magne:c field Sample weight: Acquisition time: MAS rate: Sensitivity (per scan): Resolution: 50 mg 8 h 8 khz N or 33 S?? 8 mg 8 h 4 khz + 3

14 Studies of low- γ nuclei: 5 N under natural abundance 5 N- H HETCOR of amino acids through space through bond 5 N- H HETCOR of pharmaceu8cals through space γ H γ N 3 / = 3 Similar techniques can be used/developed for other low-γ nuclei in many classes of materials Need higher magnetic field!!! Althaus et al., SSNMR, 57-58, 7- (04); collabora8on with R. Schurko, University of Windsor 4

15 Half- integer quadrupolar nuclei Most NMR-active nuclei are half-integer quadrupolar: 77 out of ~0, including 7 Li, B, 7 O, 3 Na, 5 Mg, 7 Al, 33 S, 35 Cl, 39 K, 43 Ca, 55 Mn, 87 Rb, The challenge: SSNMR spectra are dominated by quadrupolar broadening m - 3/ Zeeman I-st order II-nd order ω 0 ΔE () Sta8c spectra I- st ordrer single crystal - / ω 0 +/ ω 0 ω 0 3ω 0 ΔE () ω central I- st ordrer powder ω 0 ΔE () +3/ ω central ωq = ω0 { I( I + ) 3/ 4}( 3cos β )(9cos β ) 6ω 0 () () Δ E m Typical values for 7 Al: = MHz, = 0 khz 7 Al chemical shift range at 9.4 T: 0 khz ΔE m II- nd order (CT) 5

16 Advances in NMR of quadrupolar nuclei: complete line- narrowing Symmetric transi8on under fast rota8on of the sample () ω m m = ω Q A 0 (I, p)b Q 0 (η Q ) + ω 0 ω Q A (I, p)b Q (η Q,α Q,β Q )P (cosθ) + ω 0 ω Q A 4 (I, p)b Q 4 (η Q,α Q,β Q )P 4 (cosθ) ω 0 } isotropic anisotropic where: p = m; α Q, β Q angles between QPAS and rot. axis; θ - angle between rota8on axis and B 0 ; P,4 (cosθ) nd and 4 th order Legéndre pol.; A t (I,p), i = 0,,4 - coefficients The resonance frequency also includes chemical shit ω () cs m m = mω0 + ω m m + ω m m with ω cs cs m m = + mω0[ Δδ B ( ηcs, αcs, βcs ) P (cosθ )] P (cosθ) and P 4 (cosθ) do not have a common root; MAS narrows second order broadening only by a factor of ~3; DOR, DAS and MQMAS yield isotropic spectra A. Pines et al., Mol. Phys. 65, 03 (988); JMR, 86, 470 (990); L. Frydman et al., JACS, 7, 5367 (995) 6

17 Example: mechanisms of dehydrogena:on in metal hydrides Mechanochemistry Solid- state NMR 7 Li, B, 3 Na, 7 Al DFT Modeling 7

18 Example: mechanisms of dehydrogena:on in metal hydrides B MAS Our approach:! measure D and D NMR spectra of H, 7 Li, B, 3 Na, 7 Al and other nuclei in hydrides processed under various condi8ons and in reference compounds! obtain chemical shits and quadrupolar parameters (for spins > /) to iden8fy the coordina8on geometries and chemical structures! carry the out addi8onal SSNMR experiments to probe interatomic correla8ons, molecular mo8ons, etc.! refine the structures using molecular modeling and DFT calcula8ons B MQMAS DFT (δ CS, P Q ) Need higher magnetic field!!! 8

19 Spectra of quadrupolar nuclei at ultrahigh fields ΔE () () m,ω m m B 0 4. T 9.6 T 5 T (NHMFL, resis:ve) 40 T (NHMFL, hybrid) Simulated MAS spectra of 3 Na in NaC O 4 / NaSO 4 mixture at 4. T and 36 T 7 Al MAS spectra of aluminoborate 9Al O 3 +B O 3 Transforma8onal role of ultrahigh field: at 40 T, second order quadrupolar broadening and shit are diminished; the line width is mainly due to field drit Z. Gan et al., JACS, 4, 5634 (00) 9

20 D HETCOR spectra of quadrupolar nuclei at high fields 9.4T 8.8T 8.8T 9.4T 8.8T 8.8T D 7 Al- 3 P HETCOR spectra of AlPO 4-4:! Resolu8on of MAS- based spectra at 8.8 T in (c) and (d) rivals that of MQ- HETCOR taken at 9.4 T! (not shown here) Assuming 0% efficiency of MQMAS, 8me performance at 36 T could improve by an incredible factor of (36/9.4) 5 8mes 5 x0 4 M. Pruski et al., JMR, 84, (007) 0

21 Conclusion and acknowledgments The role of ultrahigh field in SS- NMR and materials research will be transforma:onal:! drama8cally expanded capabili8es: resolu8on, detec8on limits, range of nuclei! drama8cally expanded range of applica8ons to new materials Thank you DOE, NSF and NIH for suppor:ng our science! Funding (Ames) U.S. Department of Energy, BES (DE-AC0-07CH358) Ames: T. Kobayashi I.I. Slowing J.W. Wiench V.K. Pecharsky V. Lin D. Johnson S.M. Althaus S. Gupta Coworkers/collaborators Tokyo: Y. Nishiyama (JEOL) ExxonMobil: K. Mao G. J. Kennedy Lille/Caen: J.- P. Amoureux C. Fernandez J. Trebosc