Synthesis and crystal engineering of new halogenated tetrathiafulvalene (TTF) derivatives and their charge transfer complexes and radical ion salts

Abstract

Efficient syntheses are reported for tetraiodotetrathiafulvalene 2, 4-iodo-5-methyl-4',5'-bis(methylsulfanyl)TTF 3, and 4-iodo-4',5'-bis(methylsulfanyl)TTF 4 by iodination, using perfluorohexyl iodide, of lithiated derivatives of the corresponding TTF system. Bromination and chlorination of lithiotrimethylTTF using 1,2-dibromotetrafluoroethane and hexachloroethane gave 4-bromo-and 4-chloro-4',5,5'-trimethylTTF 6 and 7, respectively. Phosphite-induced self-coupling or cross-coupling reactions of 4-iodo-1,3-dithiole-2-thione or 4,5-diiodo-1,3-dithiole-2-thione(one) half-units resulted in TTF derivatives with partial loss of the iodine substituent(s). 4,5-Dibromo-4',5'-bis(cyanoethylsulfanyl)TTF 15 was prepared by cross-coupling methodology, and converted into 4,5-dibromo-4',5'-bis(methylsulfanyl)TTF 16 by reaction with caesium hydroxide and then methyl iodide. EPR data are reported for the electrochemically generated cation radicals of trimethylTTFX derivatives (X~I, Br and Cl) 5-7, respectively. For the neutral donors, the X-ray crystal structures are reported for 2, 5, 6, tetramethylTTF 8 and 15. Structure 2 is characterised by a particularly dense packing with continuous chains of intra-stack I … I contacts (4.17-4.19 A ˚). The crystals of 6 and 8 are isomorphous, while the structure of 5 is different. The iodo-substituent in 5 affects the packing in a way the bromo-substituent in 6 does not, due to differences in specific interactions rather than steric demands of I and Br, which are similar. Structure 15 comprises face-to-face dimers with inter-dimer Br … Br (3.57 A ˚) and Br … S (3.55 A ˚) contacts: a remarkable difference in bond distances between the Br and S-substituted dithiole rings is observed. The 1 : 1 charge-transfer (CT) complexes 3?TCNQ and 4?TCNQ (TCNQ~7,7,8,8-tetracyano-p-quinodimethane, 17) display mixed stair-like stacks of alternating D and A moieties: the overall degree of CT is estimated from bond length analysis to be 0.2 e and 0.3 e, respectively. In 3?TCNQ either position of the disordered iodine atom has one short (inter-stack, but intra-layer) contact with a cyano group (I … N distances of 3.14 and 3.18 A ˚). In 4?TCNQ a similar I … N contact is much longer (3.35 A ˚). In the structure of 5 z? I 3 2 ? 1 2I2 the cation radical is disordered; dimeric cation radicals display short intra-dimer contacts (S … S 3.38-3.39 A ˚, C … C 3.35 A ˚) consistent with electron coupling. Each dimer is surrounded by four I 3 2 anions. The crystal structure of 16 z? I 3 2 is comprised of layers with interplanar separations of 3.55 A ˚. Cations of one layer overlap with anions of the next, and the packing can be described as mixed stacks parallel to the a axis. The remarkably high conductivity of this salt for a system of 1 : 1 stoichiometry (s rt ~8610 22 S cm 21 ) is ascribed to partial charge transfer (the charge on the TTF moiety is estimated as z 2 3 from bond length analysis) and a continuous system of short non-bonding contacts.

4,4′,5,5′-Tetramethyltetrathiafulvalene–1,4-dinitrobenzene (1/1)

“…However, the geometrical parameters in (I) give no indication of CT. Comparison of the TMTTF molecules in (I) and in the crystal of pure TMTTF (Batsanov et al, 2001) shows marginal (4 e.s.d.) differences in the C1 C1 H bond lengths [1.344 (3) versus 1.358 (2) A Ê ], while the CÐS bond lengths, which give the most reliable measure of the positive charge on a TTF moiety (Clemente & Marzotto, 1996), are identical.…”

Air-stable n-channel organic field-effect transistors based on a sulfur rich π-electron acceptor

“…6). [26][27][28][29] The resulting reduced Schottky barrier is another origin of the better performance of the (TTF)(TCNQ)-based transistors. [26][27][28][29] The resulting reduced Schottky barrier is another origin of the better performance of the (TTF)(TCNQ)-based transistors.…”

Investigation of crystal structure, vibrational characteristics and molecular conductivity of 2,3-dichloro-5,6-dicyno-p-benzoquinone

“…These efforts were concentrated mainly on cation radical salts of tetrathiafulvalene derivatives, obtained by electrocrystallization with various anions acting as hydrogen bond or halogen bond acceptors. Halogen bonding interactions were also explored in charge-transfer salts [2][3][4]. According to Lieffrig et al [5] 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) acts as a powerful oxidant toward iodinated TTFs and the formation of novel charge-transfer salts with original halogen bonding patterns.…”