EPR study of the x,α and β structures of lithium phthalocyanine

Abstract

The magnetic properties of the lithium phthalocyanine radical are investigated for the x,α and β crystal structures via electron paramagnetic resonance (EPR). Different magnetic behaviours (susceptibility, line shape) are evidenced in PcLi powders and interpreted in terms of the molecular packing. A Curie–Weiss susceptibility is observed for the α-phase with a mean-field temperature, T_CW of ca. 4.5±1 K, whereas a two-component susceptibility must be considered for the x-phase (powders grown in acetonitrile) involving a Curie–Weiss contribution (T_CWca. –3±1 K) and a thermally activated contribution with an activation energy E_a of ca. 0.04 eV. For the PcLi β structure two temperature domains can be distinguished: for T>50 K a Curie–Weiss susceptibility with a mean-field temperatureT_CW of ca. –60±5 K is observed while for T<20 K a Curie–Weiss-like susceptibility withT_CWca. –7±1 K dominates. The overall magnetic properties of the PcLi polymorphs are discussed in terms of McConnell’s mechanism for ferromagnetism and antiferromagnetism in solid free radicals. The magnetic properties of β-PcLi needles (magnetic susceptibility, anisotropy of spin diffusion) have been investigated. Adsorbed oxygen is shown to alter strongly the line shape, the linewidth and the g-factor anisotropy in β-PcLi crystallites and powders at temperatures below 55 K.

References

1. C. C. Leznoff and A. B. P. Lever, Phthalocyanines Properties and Applications, VCH, 1989, 1993, 1994 and 1996, vol. 1, 2, 3 and 4.
2. P. Turek, J.-J. André, A. Giraudeau and J. Simon, Chem. Phys. Lett., 1987, 134, 471.
3. P. Turek, J.-J. André, J. Simon, R. Even, B. Boudjema, G. Guillaud and M. Maitrot, J. Am. Chem. Soc., 1987, 109, 5119.
4. F. Bensebaa and J.-J. André, J. Phys. Chem, 1992, 96, 5739.
5. K. Yakushi, T. Ida, A. Ugawa, H. Yamakado, H. Ishii and H. Kuroda, J. Phys. Chem., 1991, 95, 7636.
6. M. Brinkmann, C. Chaumont, H. Wachtel and J.-J. André, Thin Solid Films, 1996, 283, 97.
7. M. Brinkmann, J.-C. Wittmann, C. Chaumont and J.-J. André, Thin Solid Films, 1997, 292, 192.
8. (a) M. Moussavi, A. De Cian, personal communication, 1993; (b) H. Sugimoto, M. Mori, H. Masuda and T. Taga, J. Chem. Soc., Chem. Commun., 1986, 962.
9. H. Wachtel, J.-C. Wittmann, B. Lotz, M. A. Petit and J.-J. André, Thin Solid Films, 1994, 250, 219.
10. H. Homborg and Chr. L. Teske, Z. Anorg. Allg. Chem., 1985, 527, 45.
11. C. J. Schramm, R. P. Scaringe, D. R. Stojakovic, B. M. Hoffman, J. A. Ibers and T. J. Marks, J. Am. Chem. Soc., 1980, 102, 6702.
12. M. Almeida, M. G. Kanatzidis, L. M. Tonge, T. J. Marks, H. O. Marcy, W. J. Mc Carthy and R. Kannewurf, Solid State Commun., 1987, 63, 457.
13. J.-J. André and M. Brinkmann, Synth. Met., 1997, 90, 211.
14. M. Brinkmann, P. Turek and J.-J. André, Thin Solid Films, 1997, 303, 107.
15. M. A. Petit, T. Thamia and R. Even, J. Chem. Soc., Chem. Commun., 1989, 15.
16. C. J. Brown, J. Chem. Soc. A, 1968, 2488.
17. M. Ashida, N. Uyeda and E. Suito, J. Cryst. Growth, 1971, 8, 45.
18. F. Iwatsu, J. Phys. Chem., 1988, 92, 1681.
19. H. Klapper, M. Kobayashi, T. Kobayashi and K. Sato, in Organic Crystals, ed. H. C. Freyhardt and G. Müller, Springer Verlag, Berlin, 1991.
20. M. Y. Ogawa, J. Martinsen, S. M. Palmer, J. L. Stanton, J. Tanaka, R. L. Greene, B. M. Hoffman and J. A. Ibers, J. Am. Chem. Soc., 1987, 109, 1115.
21. M. Y. Ogawa, B. M. Hoffman, S. Lee, M. Yudkowsky and W. P. Halperin, Phys. Rev. Lett., 1986, 57, 9.
22. J.-L. Stanger, J.-J. André, P. Turek, Y. Hosokoshi, M. Tamura, M. Kinoshita, P. Rey, J. Cirujeda and J. Veciana, Phys. Rev. B, 1997, 55, 8398.
23. J.-L. Stanger, PhD Thesis, ULP, Strasbourg, France, 1995.
24. S. Takagi and M. Date, Physica B, 1989, 155, 425.
25. P. Turek, PhD Thesis, ULP, Strasbourg, France, 1989.
26. H. Wachtel, J.-J. André, W. Bietsch and J. U. von Schétz, J. Chem. Phys., 1995, 102, 9606.
27. P. Turek, M. Moussavi, P. Petit and J.-J. André, Synth. Met., 1989, 29, F65.
28. R. Foster, Molecular Association, Academic Press, New York, 1975, p. 70.
29. P. Turek, J.-J. André, M. Moussavi and G. Fillion, Mol. Cryst. Liq. Cryst., 1989, 176, 535.
30. S. Baker, M. C. Petty, G. G. Roberts and M. V. Twigg, Thin Solid Films, 1983, 99, 53.
31. J. C. Bonner and M. E. Fisher, Phys. Rev. A, 1964, 135, 640.
32. F. Palacio, in Magnetic Molecular Materials, ed. D. Gatteschi, O. Kahn, J. S. Miller and F. Palacio, NATO ASI Series, Kluwer Academic, Serie E, vol. 198, p. 22.
33. P. Grobet, L. Van Gerven and A. Van den Bosch, J. Chem. Phys., 1978, 68, 5225.
34. B. Bleaney and K. D. Bowers, Proc. R. Soc. London, Ser. A, 1952, 214, 451.
35. P. M. Richards, Proc. Int. School of Physics, ‘Enrico Fermi’, LIX, North Holland, 1976.
36. S. Mitra, A. K. Gregson, W. Hatfield and R. R. Weller, Inorg. Chem., 1983, 22, 1729.
37. F. Bensebaa, P. Petit and J.-J. André, Synth. Met., 1992, 52, 57.
38. J. Simon and J.-J. André, in Molecular Semiconductors, Springer Verlag, Berlin, 1985, pp. 98–101.
39. L. C. Isett, G. A. Reynolds, E. M. D. Schneider and J. H. Perlstein, Chem. Phys. Lett., 1979, 67, 71.
40. C. G. Barraclough, R. L. Martin, S. Mitra and R. C. Sherwood, J. Chem. Phys., 1970, 53, 1638.
41. J. E. Drumheller, Magn. Res. Rev., 1982, 7, 123.
42. D. Gatteschi and R. Sessoli, Magn. Res. Rev., 1990, 15, 9.
43. M. Dumm, P. Lunkenheimer, A. Loidl, B. Assmann, H. Homborg and P. Fulde, J. Chem. Phys., 1996, 104, 5048.
44. H. M. McConnell, J. Chem. Phys., 1963, 39, 1910.
45. B. Gotschy and G. Denninger, Mol. Phys., 1990, 71, 169.