The title material, where TMEO-ST-TTP is 2-[4,5-bis(methylthio)-1,3-diselen
ol-2-ylidene)-5-(4,5-ethylendioxy-1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiap
entalene, shows metallic conducting behavior down to 4.2 K. X-Ray structure
analysis reveals it has the beta-type array of donors in the BEDT-TTF salt
s. A tight-binding band calculation suggests the present salt has a quasi-o
ne-dimensional Fermi surface.