Tetrathiapentalene Derivatives with Long Alkyl Chains

Bis-fused π-electron donors having alkylthio chains, CnTET-TTP (2-[4,5-bis(alkylthio)-1,3-dithiol-2-ylidene]-5-(4,5-ethylenedithio-1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene; n = 2–4) have been synthesized. C2TET-TTP (1a) forms radical-cation salts with BF4- and ClO4-, which are metallic (σrt = 900-2500 S cm-1) down to helium temperatures. The I3 salts of C3TET-TTP (1b) and C4TET-TTP (1c) are semiconductive from room temperature (σrt = 0.041 and 0.025 S cm-1, respectively). (C2TET-TTP)2ClO4 has uniform stacks of the donors, and hats an elliptical Fermi surface characteristic of two-dimensional metals. (C4TET-TTP)I3 is dimeric, and can be regarded as a band insulator. These crystal structures demonstrate the tendency that the long alkyl chains increase the anion content, and stabilize the usual stacking structure as well as the dimerization.