Effect of heteroaromatic spacers on the structure and electrical properties of cation radical salts of tetrathiafulvalene analogs

Abstract

The X-ray crystal structure of single crystals of electrocrystallized cation radical salts of 2,5-bis(1,3-dithiol-2-ylidenemethyl)-thiophene and -furan1and2 have been analysed. Both cation radicals adopt asyn conformation stabilized by strong intramolecular interactions. Bond length analysis reveals that the positive charge is delocalized over the whole molecule with enhanced delocalization for 2⁺ containing the less aromatic furan cycle. Whereas 2⁺ cation radicals are uniformly stacked along the c axis with interstack interactions, 1⁺ forms weakly interacting dimers stacked along the b axis. In agreement with an enhanced charge delocalization and increased dimensionality, 2BF₄ shows a conductivity ca. three orders of magnitude higher than 1ClO₄ .