New bi(tetrathiafulvalenyl) derivatives and their radical cations: synthetic and X-ray structural studies

A series of bi(tetrathiafulvalenyl) derivatives has been prepared from iodo-TTF precursors by Ullmann coupling (copper in refluxing N,N-dimethylformamide) or by reaction with copper(I) thiophene-2-carboxylate (CuTC) in 1-methylpyrrolidin-2-one at 20 °C. Solution electrochemical and UV-VIS spectroscopic studies suggest that there is no significant through-bond interaction between the two TTF units in these systems. The X-ray crystal structures are reported for 4,5,5′,5′′,4′′′,5′′′-hexakis(methylsulfanyl)-4′,4′′-bitetrathiafulvalene 9 and a semiconducting 1∶1 perchlorate salt of 4,5:4′′′,5′′′-bis(ethylenedithio)-5′,5′′-dimethyl-4′,4′′-bitetrathiafulvalene 8+··ClO4−. The torsion angle around the central bond is 89° in 9 and 77° in 8+··ClO4−. The crystal packing of 8+··ClO4− is characterised by puckered layers, parallel to the (001) plane, of cations contacting via their sulfur atoms; the anions occupy infinite channels, parallel to the z-axis and running through the cation motif.