Tetrathiapentalene-type donors containing (thio)pyran-4-ylidene as a promising -electron framework for multi-dimensional molecular conductors

Abstract
The conducting materials based on 2-(1,3-dithiol-2-ylidene)-5-(pyran-4-ylidene)-1,3,4,6-tetrathiapentalene (PDT-TTP) and its thiopyran and/or selenium analogues have been developed. The ethylenedithio derivative (ET-PDT) affords 4:1 salt with PF ₆^- anion (ET-PDT) ₄PF ₆(cn) (cn = 1-chloronaphthalene). It has the so-called -type array of the donors with quasi one-dimensional electronic structure due to strongly tetramerized stack. On the other hand, (TM-TPDS) ₂AsF ₆ adopt the "windmill type" array of the donors. In this salt, relatively large side-to-edge interactions stabilize their electronic structure, while effective side-by-side interaction is inhibited by methythio groups projected along the molecular short axis. In contrast, edge-to-edge interactions are dominant in (SM-PDT)PF ₆(PhCl) _x through selenium-selenium contacts along the molecular long axis. (ET-PDT) ₄PF ₆(cn) shows metallic conductivity down to 1.5 K, while (TM-TPDS) ₂AsF ₆ is an organic metal exhibiting MI transition at 100 K. On the other hand, (SM-PDT)PF ₆(PhCl) _x is a semiconductor with relatively high conduuctivity of  S cm ^-1 in spite of 1:1 composition. Key words. tetrathiapentalene - X-ray structure analysis - electrical conductivity.