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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...

The synthesis of dicyanooligothiophenes NC(C4H2S)nCN (n = 3−6) is reported. For n = 3, 4, and 5 the dinitriles are generated by treatment of the corresponding dibromo compounds with copper(I) cyanide in quinoline. For n = 6 the preparation involves the Ni-catalyzed coupling of 5-bromo-2,2‘:5‘,2‘‘-terthiophene-5‘‘-carbonitrile. The structures of all four dicyano derivatives have been determined by X-ray crystallography. For n = 3, the space group is monoclinic C2/c, with a = 18.363(7), b = 11.8356(9), c = 30.666(4) A, β = 102.15(2)°, V = 6515(3) A3, Z = 20. For n = 4 the space group is triclinic P1, a = 7.3254(9), b = 7.8658(6), c = 8.1813(8) A, α = 64.706(8), β = 76.059(8), γ = 76.692(8)°, V = 409.29(7) A3, Z = 1. For n = 5 the space group is monoclinic C2/c, with a = 13.633(4), b = 11.706(5), c = 37.073(8) A, β = 90.22(2)°, V = 5929(3) A3, Z = 12. For n = 6, the space group is monoclinic P21/a, with a = 13.8962(14), b = 5.9100(16), c = 14.0798(16) A, β = 98.446(4)°, V = 1143.8(4) A3, Z = 2. In all four ...

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.

Ab initio molecular orbital and Møller–Plesset perturbation theory calculations have been carried out on two model dithiatriazines RCN3S2 (R = H, NH2). With geometry optimization and the inclusion of electron correlation both of these dithiatriazines are predicted to be ground state singlets. Both molecules have low-lying triplet excited states, with energy gaps of 6.6 (R = H) and 13.0 (R = NH2) kcal mol−1. The singlet dithiatriazines distort from high (C2v) to low (Cs) symmetry, and these changes are important in determining the relative energies of the singlet and triplet molecules. The structural distortions experienced by these molecules are related to Hartree–Fock and Jahn–Teller instabilities in other thiazene heterocycles.