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.

Syntheses and structures of highly soluble bis(ethylenedithio)tetrathiafulvalene molecules with alkyl chains

“…2 shows AFM images of the solution cast films of ET and C 4 ET. The thin film of ET consists of discrete microcrystals, whereas that of C 4 ET is remarkably improved in the film quality.…”

“…Along this line, we have attempted the replacement of one terminal hydrogen atom of ET by an alkyl chain (Scheme 1). Dimethyl-ET is known to form a superconductor [3], and diethyl-ET is also prepared [4], but the ET molecule with a single alkyl chain are scarcely explored, though the preparation of C 1 ET and C 17 ET has been reported [5]. In this paper, syntheses, structures, and chemical properties of C n ET (n ¼ 1-6) are reported.…”

Crystal structure of 5,6,7,8,9,10,11,12-octahydro[1,3]dithiolo[4,5-b][1,4] dithiacyclodecine-2-thione, C11H16S5

“…They were prepared for the development of electrically conducting materials and have, as such, been synonymous with the development of molecular organic metals. Based on the general synthetic strategy of TTF molecules [4][5][6][7], the key intermediates for the syntheses of TTF derivatives involve the construction of the 1,3-dithiole-2-thione ring. Among them, 4,5-bisalkylthio-1,3-dithiole-2-thione can be routinely prepared by the reaction between a zinc complex of 1,3-dithiole-2-thione-4,5-dithiolate or the anion 1,3-dithiole-2-thione-4,5-dithiolate generated in situ and suitable electrophilic reagents [8].…”

3,4-[2,2-Bis(methoxyethoxymethoxymethyl)propylenedithio]-3′,4′-(ethylenedithio)tetrathiafulvalene: a spiro-substituted BEDT–TTF analogue

“…We were interested to see whether the substituents would inhibit the usual packing modes of such donors, in which they pack in one-or two-dimensional stacks. Donors (3) (Karrer et al, 1987;Matsumiya et al, 1993), (5) (Yamada et al, 1997) and (6) (Yang et al, 2008) retain the traditional packing modes, despite the increasing bulk of the substituents, while the racemic tetraethyl donor, (4), does not (Kini et al, 1999).…”