Comparison of the Crystal and Electronic Structures of Three 2:1 Salts of the Organic Donor Molecule BEDT-TTF with Pentafluorothiomethylsulfonate Anions SF 5 CH 2 SO 3 - , SF 5 CHFSO 3 - , and SF 5 CF 2 SO 3 - Brian H. Ward, John A. Schlueter, Urs Geiser,* H. Hau Wang, Emilio Morales, James P. Parakka, Seddon Y. Thomas, and Jack M. Williams Chemistry and Materials Science Divisions, Argonne National Laboratory, Argonne, Illinois 60439-4831 Paul G. Nixon, R. W. Winter, and Gary L. Gard Department of Chemistry, Portland State University, Portland, Oregon 97207-0751 H.-J. Koo and M.-H. Whangbo Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204 Received April 26, 1999. Revised Manuscript Received November 23, 1999 Salts of the donor molecule, bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET), with pentafluorothiomethylsulfonate (SF 5 CX 2 SO 3 - ,X ) H or F) anions have been prepared. Three phases, ′′-(ET) 2 SF 5 CH 2 SO 3 , ′-(ET) 2 SF 5 CF 2 SO 3 , and ′′-(ET) 2 SF 5 CHFSO 3 were obtained by electrocrystallization with the corresponding LiSF 5 CX 2 SO 3 electrolytes. The structures of these salts were determined by single-crystal X-ray diffraction, and their physical properties were examined by electrical resistivity measurements as well as by ESR and Raman spectroscopy. The ′′-(ET) 2 SF 5 CH 2 SO 3 , ′′-(ET) 2 SF 5 CHFSO 3 and ′-(ET) 2 SF 5 CF 2 SO 3 salts are considerably different in their crystal structures, physical properties, and electronic structures despite the similarity in the structures of the SF 5 CX 2 SO 3 - (X ) H, F) anions. The ′′-(ET) 2 SF 5 - CH 2 SO 3 salt has two kinds of ET donor molecules with considerably different charge densities. The electronic structure of ′′-(ET) 2 SF 5 CHFSO 3 has both one-dimensional (1D) and two- dimensional (2D) Fermi surfaces which are similar to those found in the organic supercon- ductor ′′-(ET) 2 SF 5 CH 2 CF 2 SO 3 . The ESR data for the ′-(ET) 2 SF 5 CF 2 SO 3 salt indicate that it opens a spin gap below 45 K. The differences in the physical properties of the three salts were analyzed by calculating the HOMO-HOMO interaction energies between nearest- neighbor ET molecules in their donor molecule layers. I. Introduction Since the discovery of superconductivity in (TMTSF) 2 - ClO 4 , 1 where TMTSF refers to tetramethyltetraselena- fulvalene, a large number of organic conductors and superconductors have been prepared. The organic donor molecule, bis(ethylenedithio)tetrathiafulvalene (BEDT- TTF or ET), has led to over 50 superconducting salts. 2,3 Among these salts, κ-(ET) 2 Cu[N(CN) 2 ]Br has the high- est superconducting transition temperature T c at ambi- ent pressure (T c ) 11.6 K). 4 Superconducting ET salts with T c approaching this record were obtained by using large perfluorinated anions M(CF 3 ) 4 - (M ) Cu, Ag, Au) (T c ) 2.1-11.1 K). 5-8 More recently, the first example of an organic superconductor containing both an organic cation and an organic anion, ′′-(ET) 2 SF 5 CH 2 CF 2 SO 3 , was discovered (T c ) 5.2 K). 9 Many of the ET salts prepared with linear triatomic anions (I 3 - , IBr 2 - , AuI 2 - ,I 2 Br - , BrICl - , IAuBr - , AuBr 2 - , * To whom correspondence should be addressed. (1) Bechgaard, K.; Carneiro, K.; Rasmussen, F. B.; Olsen, M.; Rindorf, G.; Jacobsen, C. S.; Pedersen, H. J.; Scott, J. C. J. Am. Chem. Soc. 1981, 103, 2440. (2) Williams, J. M.; Ferraro, J. R.; Thorn, R. J.; Carlson, K. D.; Geiser, U.; Wang, H. H.; Kini, A. M.; Whangbo, M.-H. Organic Superconductors (Including Fullerenes): Synthesis, Structure, Proper- ties and Theory; Prentice Hall: New Jersey, 1992. (3) Ishiguro, T.; Yamaji, K. Organic Superconductors; Springer- Verlag: Berlin, Heidelberg, 1990. (4) Kini, A. M.; Geiser, U.; Wang, H. H.; Carlson, K. D.; Williams, J. M.; Kwok, W. K.; Vandervoort, K. G.; Thompson, J. E.; Stupka, D. L.; Jung, D.; Whangbo, M.-H. Inorg. Chem. 1990, 29, 2555. (5) Schlueter, J. A.; Carlson, K. D.; Geiser, U.; Wang, H. H.; Williams, J. M.; Kwok, W.-K.; Fendrich, J. A.; Welp, U.; Keane, P. M.; Dudek, J. D.; Komosa, A. S.; Naumann, D.; Roy, T.; Schirber, J. E.; Bayless, W. R.; Dodrill, B. Physica (Amsterdam) 1994, C233, 379. (6) Schlueter, J. A.; Williams, J. M.; Geiser, U.; Dudek, J. D.; Sirchio, S. A.; Kelly, M. E.; Gregar, J. S.; Kwok, W. K.; Fendrich, J. A.; Schirber, J. E.; Bayless, W. R.; Naumann, D.; Roy, T. J. Chem. Soc., Chem. Commun. 1995, 1311. (7) Schlueter, J. A.; Williams, J. M.; Geiser, U.; Dudek, J. D.; Kelly, M. E.; Sirchio, S. A.; Carlson, K. D.; Naumann, D.; Roy, T.; Campana, C. F. Adv. Mater. 1995, 7, 634. (8) Schlueter, J. A.; Geiser, U.; Wang, H. H.; Kelly, M. E.; Dudek, J. D.; Williams, J. M.; Naumann, D.; Roy, T. Mol. Cryst. Liq. Cryst. 1996, 284, 195. 343 Chem. Mater. 2000, 12, 343-351 10.1021/cm990238q CCC: $19.00 © 2000 American Chemical Society Published on Web 01/25/2000