The S-Se-N-based heterocycle benzo[2,1-c:3,4-c ' ]bis(1,2,3-thiaselenazole) (BSe) can be prepared by the condensation of 1,4-diaminobenzene-2,3-dithiol with selenium tetrachloride. Crystals of this. compound are not isomorphous with the related benzo[2,1-c:3,4-c ' ]bis(1,2,3-dithiazole) (BT); a structure is adopted that allows for more extensive intermolecular Se- - -Se contacts. Electro-oxidation of BSe in the presence of [n-Bu4N][ClO4] affords metallic green needles of the charge transfer salt [BSe]3[ClO4](2), which exhibit a pressed pellet conductivity sigma (RT) = 10(-1) S cm(-1). The crystal structure of [BSe](3)[ClO4](2) consists of slipped pi -stacks based on the triple-decker building block. The packing is analogous to that found for the charge transfer salt decker closed shell [BSe](3)(2+) building block. The packing is analogous to that found for the charge transfer salt [BT](3)[FSO3](2), for which sigma (RT) = 10(-2) S cm(-1). Extended Mickel band structure calculations on these two (sulfur- and selenium-based) 3:2 salts reveal more extensive intermolecular interactions in the selenium compound. As a result, the latter has a more two-dimensional electronic structure. Crystal data for Se2S2N2C6H2, a = 4.103(2) Angstrom, b = 12.159(2) Angstrom, c = 16.171(2) Angstrom, orthorhombic, Pbnm, Z = 4. Crystal data for Se6S6N6C18H6C2O4, a = 17.00(1) Angstrom, b = 18.36(1) Angstrom, c = 10.679(4) Angstrom, 110.27(3), monoclinic, C2/c, Z = 4.