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The characterization of the heterocyclic radical 1,2,5-thiadiazolo[3,4-b]-1,3,2-dithiazolo[3,4-b]pyrazin-2-yl (TDP-DTA) is described. The compound is prepared by treatment of 5,6-dithiolo-1,2,5-thiadiazolo[3,4-b]pyrazine with S3N3Cl3 and purified by fractional sublimation in vacuo. The results of cyclic voltammetry and ESR analysis of TDP-DTA and related heterocyclic dithiazolyls indicate that the spin distributions and donor/acceptor properties of these radicals are extremely sensitive to the nature of the 4,5-substituents. The crystal structure of TDP-DTA has been determined at two temperatures. At 293 K, the crystals are triclinic, space group P1, with a = 4.4456(8), b = 8.407(2), c = 9.671(3) A, α = 71.34(2), β = 89.28(2), γ = 87.80(2)°, Z = 2 (for C4N5S3); at 150 K the crystals are triclinic, space group P1, with a = 7.489(7), b = 9.593(4), c = 10.759(6) A, α = 65.77(4), β = 74.10(6), γ = 74.64(6)°, Z = 2 (for C8N10S6). At 293 K the structure consists of ribbons of TDP-DTA radicals packed in a slip...

MOST molecular conductors rely on charge transfer to create carriers. For example, the ET salts1 are hole-doped whereas the C60 salts2 are electron-doped. Neutral radical species in which bands are formed by π-orbital overlap would be expected to have half-filled bands and thus to be conducting3, but no such metals have yet been reported. Here we report the synthesis and characterization of a molecular conductor which combines both of these approaches: energy bands are formed from one-dimensional stacks of neutral π-radicals, and the material is rendered conducting by electron transfer from the conduction band following doping with an acceptor. The radical species is the l,4-phenylene-bis(dithiadiazolyl) diradical 1,4-[(S2N2C)C6H4(CN2S2)] (2 in Fig. 1), reaction of which with iodine vapour leads to crystals of [2][I]. At low temperatures this compound is essentially a diamagnetic insulator, but above 200 K the conductivity and magnetic susceptibility increase markedly, and at room temperature the conductivity reaches l00 S cm−1, which is comparable to that shown by conventional molecular charge-transfer salts.