High Resolution Solid State NMR in Paramagnetic Materials

1. High Resolution Solid State NMR in Paramagnetic Materials

2. Solid State MAS NMR • a powerful tool in model inactive materials • can we us it in real radioactive materials? • Radioactivity and NMR ? • Sample confinement (cf. Dimitri Sakellariou lecture) • Radioactive  paramagnetic ! • MAS NMR in paramagnetic materials? • Much less publications than for diamagnetic materials • Why? • Huge interactions with the electronic moments • In Nuclear wastes • Paramagnetism comes from • Irradiation deffects • Actinides • Fission products (Few exceptions: 3H,Cs,...)

3. Larmor Precession +Environment EPR, Magnetic Susceptibility, Optical Spectroscopy...... Brownian Motion MAS DAS/DOR MQMAS High Resolution Magnets Lanthanides Actinides Paramagnetics Paramagnetics Electronic relaxation Symmetry of the Interactions New methods? Liquid  Solid LanthanidesActinides NMR in Solids NMR in Liquids NMR in Paramagnetic Solids High Resolution NMR in Liquids High Resolution NMR in Solids High Resolution NMR in Paramagnetic Liquids High Resolution NMR in Radioactive Solids « pour l ’aval du cycle » Confinment, Radiologic Protection,...

4. Diamagnetic Solids-->Paramagnetic Solids • -What new for NMR? Electronic magnetic moments. µe=653µn • - Interaction with electronic magnetic moments. • -Two more interactions: Contact and pseudo-contact • - Second, third,....neigbour shifts agree with through space dipolar interaction with the dipole at the center of the paramagnetic nucleus. • -First neigbour interaction much greater than that dipolar interaction. Highly anisotropic. (Dipolar interaction with elecrons not at the center, but closer to the 19F, in the orbitals?) • - Huge interactions. The dipolar field created by an electron at 2Å is 1150 gauss (to be compared with 1,75 gauss for a proton). • -Motional Line narowing • Electronic relaxation • - fortunately, for most lanthanides and actinides: • fast relaxation averaging-> narrow lines • - for some lanthanides and actinide (Gd3+, Cm3+,...): • slower relaxationsevere relaxation broadening • Electronic flip-flops • Makes the average contact shift field dependent as is always the pseudocontact shift

6. Huray P.G and Nave S.E., p.311, Handbook of the Physics and Chemistry of the Actinides, Freeman A.J. and Lander G.H. Editors, Elsevier 1987

7. Yb3+ in CaF2 As: Measured Isotropic interaction Ap: Measured Anisotropic interaction (dipolar angular dependence) Ad: Dipolar interaction calculated with electronic dipole at the origin Isotropic g=3.443 D.Kiro & W.Low, Phys.Rev.Lett.,20,1010(1968)

8. Contact • - Similar to Indirect J coupling • (delocalisation of the wave function of the paramagnetic atom) • - Huge an very short range • - Greater than the dipolar interaction for the first neighbours • - Much smaller for the next neighbours • (if no covalent bonding to the first ones) • - Is often told to be isotropic, but may be very anisotropic • (vg.: Yb3+ (isotopic g) in cubic CaF2 • - Shifts dues to the neighbour electronic spins are additive • so that one observe • - yet resolved spectra if those spins are « equivalent » • (cf 119Sn and 89Y in pyrochlores) • - severe broadening if they are non equivalentand more than one of these sites is occupied (31P in monazites)

11. 3.18 98.6 101.2 3.72 142.8 139.2 3.72 128.9 3.71 3.72 136.8 3.76 94.5 105.5 3.26 109.9 3.72 3.72 3.18 3.26 142.8 139.2 3.76 3.72 136.8 128.9 109.9 3.71 Monazite....

14. Pseudo-Contact • Dipolar interaction •  broadening in diamagnetics, shift (and broadening) in paramagnetics. Why? • Dipolar shift in Static solids • - Constant within an ellipsoid, nuclear position dependent for any other sample shape: cubes, parallelepipeds,... • - 1/r3 dependence  shifts are due to sample shape (non spherical) as well as to local order (non cubic). Cannot be distinguished. • - Slow convergence (at variance with the 1/r6 dependence for the dipolar second moment). But here, the “not squared angular factors” may cancel, so that convergence is accelerated in cubic samples with cubic or amorphous crystallographic structure. • - Concentration dependence of the “bulk”/”local” contributions • Dipolar shift in liquids, the isotropic shift • - Calculated by Bleaney(JMR,8,91(1972)) for liquids • Dipolar shift in rotating solids: • - residual anisotropic susceptibility broadening: one cannot always apply Bleaney calculation! • - axial, cubic, glassy solids (crystal structure)- powder samples

15.  Rotation à l’angle magique 

20. Improving the resolution -Susceptibility matching -PASS -….

21. Susceptibility Matching

22. PASS Elimination of rotational sidebands MAS splits a broad line into a comb of narrower rotational sidebands. If the linewidth of the sidebands is not smaller than the rotational frequency, the NMR remains a broad line without structure. The elimination of the sidebands by the PASS method (Thibault Charpentier) makes the structure of the spectrum appear.

25. High resolution NMR in paramagnetic materials? - Small concentrations - Selective averaging

26. High Resolution requires low concentrations ? Useful concentrations may be high (up to 30%) Small concentrations no contact interaction no bulk susceptibility broadening “No” means “smaller than differences in chemical shifts which are signficant in diamagnetic cmpounds”

27. Dependance on concentration High concentration: all the nuclei are close to several paramagnetic atoms: severe broadeningunless the paramagnetic sites are equivalents Medium concentration: each nucleus has one paramagnetic neighbour. The spectrum is resolved. But the contact shift may dominate the peudo-contact and chemical shifts. Low concentration: most of the nuclear nuclei have zero paramagnetic neighbour. Only pseudo-contact and chemical shifts as well as quadrupolar shift are efective. NB: The relative weight of bulk susceptibility effects/over local environment effects decreases as the concentration.

28. Small concentrations In YPO4(xenotime, isostrucural to Zircon), how much 31P are remote by more than « d » Å from any rare eath cd>4Å d>6Å d>10Å 30% 11.7% 0.16% 0.0004% 10% 53% 15% 0.6% 5% 73% 39% 8.5% 2% 88% 69% 38% 1% 94% 83% 62% where « c » is the rare eath concentration no rare earth as a first neighbour

29. Selective averaging Selective averaging of - bulk sample shifts by Zero Quantum experiments - any paramagnetic shifts by sheared MAQMAS (11B,17O,…) expected to work even in presence of strong paramagnetic broadening

33. ...from NMR spectra to structural data…. In diamagnetic materials this is achieved - by using a huge corpus of experimental NMR data previously measured on compounds of well known structure - by computation

34. ...from NMR spectra to structural data…. In paramagnetic materials - a prequisite step is the separation of the local order contribution to the shifts from the bulk susceptibility effects - especially for actinide compounds, there is no corpus of experimental data in compounds of known structure. Such data must be acquired before trying to get reliable structural informations in disordered materials.

35. Computation of the interactions in paramagnetic materials 1) Electronic delocalisation (« contact ») The next neighbours are blurred by «  contact » shift and broadening. Needs very careful and accurate theoretical chemistry calculations (in progress, cf. Thibault Charpentier lecture).

36. 2) Electronic dipolar field («pseudo-contact ») Easier than that of the « contact » shift. As a prerequisite, one must be able to distinguish the contribution of the local environement and that of the bulk sample. If this is acquired, then, the 1/r3 dependence is easy to calculate. Last, the shift is proportional to the anisotropy af the magnetic susceptibility, which has been calculated by Bleaney for the rare earths within in the formalism of the crystalline field, in the approximation ofRussel-Saudres and with the assumption that the spliting of the fundamental multiplet is less than kT. These assumptions are not so well justified for the actinides. In a first step (en cours), one may try to extrapolate the Bleaney calculation to the actinides. In any case, as already told, one must get experimental spectra inactinide compounds of well known structure (for direct use as reference spectra and for validation of the calculations). In a second step, we shall need wave functions established by « ab initio » or DFT calculations. One may also think about direct measurements of the magnetic susceptibility. Hovever its anisotropic and not the average suceptibility is required. How to measure it in powders or amorphous materials? Monocrystals are needed.

37. Anisotropy of the magnetic susceptibility of lanthanides, measured in a protein matrix Bertini I, and al., JACS, 2001,123,4181-4188

38. Extrapolation lanthanidesactinides

39. Proxys A Warning: Proxys for chemical properties may not be proxys for magnetic properties!

40. Extrapolation lanthanidesactinides Experimental results seems to indicate that the average susceptibility follows, as the lanthanides, the simple rule où Huray P.G and Nave S.E.,op.cit.

41. What Magnetic Field? Sensitivity or Resolution? In a first approximation, for a given sample the signal to noise ratio increases with the magnetic field, according to if the line width is proportional to the field (distribution of chemicalshifts, paramagnetic broadening,........) if the line width does not depend on the field If one takes into account the variation of the quality factor Q with frequency (including the skin depht effect) that is , these expressions become and Thus the sensitivity increases with the field, together with the shifts and broadening due to the paramagnetics, whereas decreases the second order quadrupolar interaction which may afford the resolution for quadrupolar nuclei. Does one has to choose a very high field?

42. Catherine Kiener Edgar Soulié Gérard Folcher Paul Rigny Maurice Goldman Anatole Abragam Michel Ephritikine Hervé Desvaux Dominique Massiot Aknowledgements Thibault Charpentier, Dimitri Sakellariou Jacques François Jacquinot Francine Brunet and many others from the French Solid State NMR GDR from the CEA and the CNRS from France and from other countries Service de Chimie Moléculaire, Département d’Etudes sur la matière Condensée, les Atomes et les Molécules, Direction des Sciences de la Matière, Commissariat à L’Energie Atomique - Centre d’Etudes Nucléaires de Saclay CEA/CEN Saclay/DSM/DRECAM/SCM September 2005

43. Electronic Magnetic Moments The magnetic moment of one electron is 653 times higher than that of a proton. The dipolar field created by an electron at 2Å is 1150 gauss (to be compared with 1,75 gauss for a proton) This will induce huge NMR shifts. Will that huge dipolar field dominate the other interactions? Does it bring a structural information?