Chiral Radical Cation Salts of Me-EDT-TTF and DM-EDT-TTF with Octahedral, Linear and Tetrahedral Monoanions

Methyl-ethylenedithio-tetrathiafulvalene (Me-EDT-TTF (1) and dimethyl-ethylenedithio-tetrathiafulvalene (DM-EDT-TTF (2) are valuable precursors for chiral molecular conductors, which are generally obtained by electrocrystallization in the presence of various counter-ions. The number of the stereogenic centers, their relative location on the molecule, the nature of the counter-ion and the electrocrystallization conditions play a paramount role in the crystal structures and conducting properties of the resulting materials. Here, we report the preparation and detailed structural characterization of the following series of radical cation salts: (i) mixed valence (1)(2)AsF6 as racemic, and (S) and (R) enantiomers; (ii) [(S)-1]AsF6 center dot C4H8O and [(R)-1]AsF6 center dot C4H8O where a strong dimerization of the donors is observed; (iii) (1)I-3 and (2)I-3 as racemic and enantiopure forms and (iv) [(meso)-2]PF6 and [(meso)-2]XO4 (X = Cl, Re), based on the new donor (meso)-2. In the latter, the two methyl substituents necessarily adopt axial and equatorial conformations, thus leading to a completely different packing of the donors when compared to the chiral form (S,S)/(R,R) of 2 in its radical cation salts. Single crystal resistivity measurements, complemented by thermoelectric power measurements in the case of (1)(2)AsF6, suggest quasi-metallic conductivity for the latter in the high temperature regime, with sigma(RT) approximate to 1-10 S cm(-1), while semiconducting behavior is observed for the (meso)-2 based salts.

Automated summary

This study presents the preparation and structural characterization of a series of radical cation salts, investigating the impact of stereogenic centers, counter-ion nature, and electrocrystallization conditions on the crystal structures and conducting properties of the materials. Single crystal resistivity measurements show quasi-metallic conductivity for certain salts, while semiconducting behavior is observed for others.