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14 N NQR study of proton position and dynamics in some hydrogen bonded organic ferroelectrics

14 N NQR study of proton position and dynamics in some hydrogen bonded organic ferroelectrics. Janez Seliger 1 , Veselko Žagar 1 , Tetsuo Asaji 2 1 “Jozef Stefan” Institute, Jamova 39, 1000 Ljubljana, Slovenia

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14 N NQR study of proton position and dynamics in some hydrogen bonded organic ferroelectrics

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  1. 14N NQR study of proton position and dynamics in some hydrogen bonded organic ferroelectrics Janez Seliger1, Veselko Žagar1, Tetsuo Asaji2 1 “Jozef Stefan” Institute,Jamova 39, 1000 Ljubljana, Slovenia 2Department of Chemistry, College of Humanities and Sciences, NihonUniversity, Sakurajosui 3-25-40, Setagaya-ku, Tokyo 156-8550, Japan

  2. Outline • 14N NQR • 1H-14N NQDR • Hydrogen bonded organic ferroelectrics - phenazine–chloranilic acid (1:1) - 1,2-diazine–chloranilic acid (2 : 1) - 2,3,5,6-tetra(2’-pyridyl)pyrazine-chloranilic acid (1:2) • Conclusions

  3. Nuclear quadrupole energy levels

  4. 14N NQR frequencies and spin-lattice relaxation rates - local origin - sensitive to small changes in the electron charge distribution

  5. Nuclear quadrupole double resonance (NQDR): indirect detection of 14N,17O, ... • Invented by Prof. E. L. Hahn, Berkeley, CA, USA • Further developed in various laboratories: - London, UK (Prof. J. A. S. Smith) - Oxford, UK (Prof. D. T. Edmonds) - Urbana, IL, USA(Prof. T. L. Brown) - Kaliningrad, Russia (Prof. V. Grechishkin) - Ljubljana, Slovenia (Prof. R. Blinc)

  6. Basic detection procedure: Magnetic field cycling

  7. 1H-14N NQDR techniques • Level crossing - Blinc et al, J. Chem. Phys. 57 (1972) 5087 • Edmonds, Phys. Rep. 29 (1977) 234 • Cross relaxation spectroscopy • Seliger et al, J. Chem. Phys. 65 (1976) 2887 • Stephenson, Smith, Proc Roy. Soc. A 416 (1988) 149 • Solid effect • Seliger, Žagar, J. Magn. Reson. 193 (2008) 54 • Frequency sweeps, 2-frequency irradiation - Seliger et al, J. Magn. Reson. A 106 (1994) 214       

  8. Cocrystal phenazine-chloranilic acid (1:1)organic ferroelectric

  9. 14N NQR results

  10. 14N NQR results

  11. 1,2-diazine-chloranilic acid (2:1)

  12. 14N NQR frequencies

  13. 14N e2qQ/h and h

  14. X-ray diffraction data

  15. Principal values of the EFG tensor

  16. The extreme values (eQVii/h)1 and (eQVii/h)2 (i = X, Y, Z)

  17. Correlation diagram

  18. X-ray diffraction + 14N NQR • The weight of the state O-H...N increases with increasing temperature. • The weight of the state O-...H-N+ decreases with increasing temperature. • The ionic character of the state O-...H-N+ increases with increasing temperature. • The double-well potential displaces in the direction N→O with increasing temperature.

  19. Solely 14N NQR (adjustable DE)

  20. 2,3,5,6-tetra(2’-pyridyl)pyrazine (TPPZ) - chloranilic acid (1:2) (ferroelectric)

  21. 1H-14N NQDR T<Tc

  22. 14N NQR results T = 145 K < Tc

  23. Correlation of the principal values of the quadrupole coupling tensor for pyridine

  24. 1H-14N cross-relaxation spectra at T > Tc =172 K

  25. 1H-14N cross-polarization spectra T > Tc

  26. Exchange (T > Tc): N(1a)-H+...N(2a) ↔ N(1b)...H+-N(2b) t(room temperature) ≈ 1 ms Ea = kB.4200 K

  27. Conclusions • 14N NQR reflects hydrogen position, displacements and exchange in hydrogen bonds. • It can be used to study local structure and dynamics of ferroelectrics and other hydrogen bonded solids, where nitrogen participates as either the hydrogen bond acceptor or the hydrogen bond donor.

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