New Molecular Conductors Based on ETEDT-TTF Trihalides: From Single Crystals to Conducting Layers of Nanocrystals M. Mas-Torrent, † E. Ribera, † V. Tkacheva, ‡ I. Mata, † E. Molins, † J. Vidal-Gancedo, † S. Khasanov, § L. Zorina, § R. Shibaeva, § R. Wojciechowski, | J. Ulanski, | K. Wurst, ⊥ J. Veciana, † V. Laukhin, †,‡,# E. Canadell, † E. Laukhina, †,‡ and C. Rovira* ,† Institut de Cie ` ncia de Materials de Barcelona, CSIC, Campus Univeritari de Bellaterra, E-08193 Cerdanyola, Spain, Institut of Problems of Chemical Physics and Institut of Solid State Physics, RAS, 142432, Chernogolovka, MD, Russia, Department of Molecular Physics, Technical University of Lodz, 90-924 Lodz, Poland, and Institute fu ¨ r Allgemeine Anorganische und Theoretische Chemie, Universita ¨ t Innsbruck, Innrain 52a, A-6020 Innsbruck, Austria Received January 22, 2002. Revised Manuscript Received April 3, 2002 Electrocrystallization of the novel π-electron donor (ethylenethio)(ethylenedithio)- tetrathiafulvalene (ETEDT-TTF) with trihalide anions has given rise to a new family of radical cation salts with insulating properties, [ETEDT-TTF]X, and conducting properties, ETEDT-TTF]X 0.42 , where X ) I 3 - or I y Br 3-y - . According to X-ray data, in the isostructural completely ionic [ETEDT-TTF]X salts, the donor radical cations are strongly dimerized, with an interplane distance of 3.310-3.317 Å, and the mixed-valence [ETEDT-TTF](I 3 ) 0.42 salt is formed by segregated radical cation and anion layers alternating along the b axis. The latter salt exhibits semiconductor behavior with a high room-temperature conductivity of 24 S‚cm -1 . The large angle between the molecular planes of the donors in neighboring stacks precludes the possible metallic behavior of this salt. Interestingly, nanocrystals of the mixed-valence salts are the conducting component of new bilayer (BL) composite films that have been generated via the ETEDT-TTF + I 2 and ETEDT-TTF + IBr chemical reactions. The structure and composition of the conducting layers of these new BL films were confirmed by X-ray, EPR, and Raman spectroscopies. Similarly to the single crystals, these composite materials exhibit semiconducting behavior with a room-temperature conductivity ranging from 0.25 to 2.5 S‚cm -1 . SEM and NIR studies of the film samples were also carried out. Introduction Since the discovery of the first organic metal TTF- TCNQ in 1972, 1 the development of new π-electron donors based on tetrathiafulvalene and its analogues has remained at the forefront of research in the field of organic metals, resulting in a multitude of metals and superconductors. In the search for electron-donor mol- ecules as sources for new organic superconductors, multichalcogen TTF derivatives have been the most successful choice. The main reason for this success is their ability to produce 2D electronic structures through S‚‚‚S contacts while avoiding the observed structural changes that promote metal-to-insulator transitions in 1D conductors, and hence, allowing the transition to the superconducting state. 2 To date, the bis(ethylenedithio)- tetrathiafulvalene (BEDT-TTF) donor has provided the largest number of molecular superconductors 2b and forms the salt with the highest known T c , 12.8 K. 3 Following this approach in the design of new organic conductors with external sulfur atoms, our group previ- ously synthesized a new disymmetric donor ETEDT- TTF [(ethylenethio)(ethylenedithio)tetrathiafulvalene] that can be considered as a combination of one-half BEDT-TTF and one-half BET-TTF (Scheme 1). 4 The latter donor gives rise to a family of isostructural salts with octahedral counteranions XF 6 - (X ) P, Sb, As) that exhibit stable metallic properties, and thus, it seems to be a good building block for the synthesis of organic * Author for correspondence: Dr. C. Rovira,e-mail: cun@icmab.es. Address: Institut de Cie ` ncia de Materials de Barcelona, Campus UAB, E-08193Bellaterra,Spain.Telephone: +34935801853.Fax: +34935805729. † Institut de Cie `ncia de Materials de Barcelona, CSIC. ‡ Institut of Problems of Chemical Physics, RAS. § Institut of Solid State Physics, RAS. | Technical University of Lodz. ⊥ Universita ¨ t Innsbruck. # Present affiliation: Institucio ´ Catalana de Recerca i Estudis Avanc ¸ ats (ICREA), Pg. Lluis Companys 23, 08010 Barcelona, Spain (1) Ferraris, J.; Cowan, D. O.; Walatka, V. V.; Perlstein, J. H. J. Am. Chem. Soc. 1972, 94, 3372. (2) (a) The Physics and Chemistry of Organic Superconductor; Saito, G., Kagoshima, S., Eds.; Springer: Berlin, 1990. (b) Organic Super- conductor (Including Fullerenes). Synthesis, Structure, Properties and Theory; Williams, J. M., Ferraro, J. R., Thorn, R. J., Carlson, K. D., Geiser, U., Wang, A H. H., Kini, M., Whango, M.-H., Eds.; Prentice Hall: Upper Saddle River, NJ, 1992. (3) Williams, J. M.; Kini, A. M.; Wang, H. H.; Carlson, K. D.; Geiser, U.; Montgomery, L. K.; Pyrca, G. J.; Watkins, D. M.; Kommers, J. M.; Boryschuk, S. J.; Crouch, A. V. S.; Kwok, W. K.; Schirber, J. E.; Overmyer, D. L.; Jung, D.; Whangbo, M.-H. Inorg. Chem. 1990, 29, 3262. (4) Ribera, E.; Veciana, J.; Molins, E.; Mata, I.; Wurst, K.; Rovira, C. Eur. J. Org. Chem. 2000, 2867. 3295 Chem. Mater. 2002, 14, 3295-3304 10.1021/cm021123g CCC: $22.00 © 2002 American Chemical Society Published on Web 06/26/2002