Preparation, structures and physical properties of selenium analogues of DTEDT as promising donors for organic metals

Three selenium analogues of DTEDT [2-(1,3-dithiol-2-ylidene)-5-[2-(1,3-dithiol-2-ylidene)ethylidene]-1,3,4,6-tetrathiapentalene] have been synthesized. They showed four pairs of single-electron redox waves. The E-1 values are a little higher by 0.02-0.05 V than that of DTEDT. On the other hand, the E-2-E-1 values are almost equal to that of DTEDT. Their TCNQ complex and cation radical salts show fairly high electrical conductivities and several salts exhibit metallic conductivities. In particular the ReO4- and Au(CN)(2)(-) salts of DTEDS and the SbF6-, TaF6- and I-3(-) salts of DSEDS exhibited stable metallic behaviour down to 1.5-4.2 K. An X-ray crystal structure analysis of the metallic salt (DSEDS)(3)TaF6 reveals that this salt has a two-dimensional beta-type packing motif of the donor molecules similar to the superconducting (DTEDT)(3)Au(CN)(2). The calculated Fermi surface of (DSEDS)(3)TaF6 is a two-dimensional closed ellipsoid.