Cation radical salts of cyano(ethylenedithio)tetrathiafulvalene with halogenated anions:: annihilation of the CN•••Hal interaction and stabilisation of conducting, antiferromagnetic square or chain-type salts

The synthesis, X-ray crystal structure and electrochemical properties of 3-cyano-3',4'-ethylenedithiotetrathiafulvalene (EDT-TTF-CN, 1) are described together with electrocrystallisation experiments in the presence of various halogenated anions, I-3(-), FeBr4-, InBr4-, AuBr4-, Mo6Br142-, Mo6Cl8Br62-. X-Ray crystal structures are described for each salt, characterised by a systematic absence of any short and directional CN . . . Hal interactions, convincing evidence of the electrostatic character of this interaction, which is enhanced in the opposite situation where cationic halogenated tetrathiafulvalenes are associated with cyanide anions such as Ag(CN)(2)(-).This behaviour is further rationalised by atomic population calculations on TTF-CN and [TTF-CN](.+) which confirm the strong decrease of the negatively charged character of the nitrogen atom upon TTF-CN oxidation to [TTF-CN](.+) A conducting mixed-valence salt is obtained in [1](2)[I-3],which exhibits an unusual structure with the I-3(-) anions embedded in the organic conducting layer. All the other salts contain fully oxidised [1](.+) radical cations, associated into diamagnetic diads in [1][I-3], [1](2)[Mo6Br14][CH3CN](4) and [1](2)[Mo6Cl8Br6][CH3CN](4), into spin chains in the two isostructural [1][FeBr4]and [1][InBr4]salts and into a quadratic two-dimensional spin system in [1][AuBr4].