Tetraalkyl- and dialkyl-substituted BEDT-TTF derivatives and their cation-radical salts: synthesis, structure, and properties

Abstract

Tetraalkyl and dialkyl derivatives, where alkyl=ethyl and propyl, of the organic electron donor molecule bis(ethylenedithio)tetrathiafulvalene, BEDT-TTF or ET, have been synthesized via the Diels-Alder approach. Several cation-radical salts of these new donors have been prepared and structurally characterized, and found to contain donor molecules in nominally higher oxidation states (+1, +1.5 and +2) than the typically observed oxidation state of +0.5 in BEDT-TTF salts. The higher solubility of the tetraalkyl and dialkyl derivatives in solvents used for crystal growth is proposed as the principal reason for this finding. Surprisingly, X-ray crystallographic studies reveal that the alkyl groups in the neutral tetraethyl-ET as well as the oxidized tetraethyl-ET and diethyl-ET molecules in their cation-radical salts adopt axial configurations, rather than the expected equatorial configurations. Electrical properties of the cation-radical salts have been found to be either insulating or semiconducting, consistent with the higher oxidation states of the donor molecules in the salts and the crystal structures.

References

1. See e.g., Special Issue on Molecular Conductors, J. Mater. Chem., 1995, 10, 1469.
2. L. G. Caron, in Organic Conductors—Fundamentals and Applications, ed. J.-P. Farges, Marcel-Dekker, New York, 1994, Ch. 2, pp. 25–73.
3. (a) J. M. Williams, J. R. Ferraro, R. J. Thorn, K. D. Carlson, U. Geiser, H. H. Wang, A. M. Kini and M.-H. Whangbo, Organic Superconductors (Including Fullerenes), Prentice Hall, Englewood Cliffs, NJ, 1992; (b) T. Ishiguro and K. Yamaji, Organic Superconductors, Springer-Verlag, Berlin Heidelberg, 1990.
4. (a) J. Hellberg, K. Balodis, M. Moge, P. Korral and J.-U. von Schütz, J. Mater. Chem., 1997, 7, 31; (b) J. Yamada, S. Mishima, H. Anzai, M. Tamura, Y. Nishio, K. Kajita, T. Sato, H. Nishikawa and K. Kikuchi, Chem. Commun., 1996, 2517; (c) Y. Misaki, T. Ohta, N. Higuchi, H. Fujiwara, T. Yamabe, T. Mori, H. Mori and S. Tanaka, J. Mater. Chem., 1995, 5, 1571; (d) A. J. Moore, M. R. Bryce, D. J. Ando and M. B. Hursthouse, J. Chem. Soc., Chem. Commun., 1991, 320; (e) T. K. Hansen, M. V. Lakshmikantham, M. P. Cava and J. Becher, J. Chem. Soc., Perkin Trans. 1, 1991, 2873.
5. (a) J. D. Wallis, A. Karrer and J. D. Dunitz, Helv. Chim. Acta, 1986, 69, 69; (b) A. I. Kotov, C. Faulmann, P. Cassoux and E. B. Yagubskii, J. Org. Chem., 1994, 59, 2626.
6. A. M. Kini, U. Geiser, H. H. Wang, K. R. Lykke, J. M. Williams and C. F. Campana, J. Mater. Chem., 1995, 5, 1647.
7. J. P. Parakka, A. M. Kini and J. M. Williams, Tetrahedron Lett., 1996, 37, 8085.
8. J. M. Williams, Mol. Cryst. Liq. Cryst., 1996, 284, 449.
9. (a) C. Benming, F. Deilacher, M. Hoch, H. J. Keller, P. Wu, P. Armbruster, R. Geiger, S. Kahlich and D. Schweitzer, Synth. Met., 1991, 42, 2101; (b) S. Matsumiya, A. Izuoka, T. Sugawara, T. Taruishi and Y. Kawada, Bull. Chem. Soc. Jpn., 1993, 66, 513.
10. J. S. Zambounis, C. W. Mayer, K. Hauenstein, B. Hilti, W. Hofher, J. Pfeiffer, M. Bürkle and G. Rihs, Adv. Mater., 1992, 4, 33.
11. (a) O. Neilands, J. Kaicens and J. Kreicberga, USSR Patent #SU 1428753, 1988;; Chem. Abstr., 1989, 110, 95252k; (b) O. Neilands, J. Kacens and J. Kreicberga, Zh. Org. Khim., 1989, 25, 658.
12. V. Y. Khodorkovsky, J. Y. Becker and J. Bernstein, Synthesis, 1992, 1071.
13. Review: N. Svenstrup and J. Becher, Synthesis, 1995, 215.
14. Subsequent to the completion of our synthesis of tetraethyl-ET and tetra(n-propyl)-ET a report appeared in the literature on the Diels–Alder reaction between the trithione oligomer and trans-stilbene, see D.-Y. Noh, H.-J. Lee, J. Hong and A. E. Underhill, Tetrahedron Lett., 1996, 42, 7603.
15. T. Mori and H. Inokuchi, Chem. Lett., 1986, 2069.
16. (a) K. A. Abboud, M. B. Clevenger, G. F. de Oliviera and D. R. Talham, J. Chem. Soc., Chem. Commun., 1993, 1560; (b) K.-L. Chou, M. A. Quijada, M. B. Clevenger, G. F. de Oliviera, K. A. Abboud, D. B. Tanner and D. R. Talham, Chem. Mater., 1995, 7, 530.
17. (a) R. P. Shibaeva, R. M. Lobkovskaya, É. B. Yagubskii and E. É. Kostyuchenko, Kristallografiya, 1986, 31, 455 (Engl. Transl. Sov. Phys. Crystallogr., 1986, 31, 267); (b) M. A. Beno, U. Geiser, K. L. Kostka, H. H. Wang, K. S. Webb, M. A. Firestone, K. D. Carlson, L. Nuñez, M.-H. Whangbo and J. M. Williams, Inorg. Chem., 1987, 26, 1912.
18. H. Yamochi, H. Urayama, G. Saito, K. Oshima, A. Kawamoto and J. Tanaka, Chem. Lett., 1988, 1211.