Preparation and Solid State Characterization of Isostructural Bifunctional 1,2,3,5-Dithiadiazolyls with Benzene, Bithiophene, and Piperazine Spacers

The preparation of the bis(1,2,3,5-dithiadiazolyl) radicals [S 2 N 2 C]−X−[CN 2 S 2 ], where X is a heterocyclic bridging group (X = piperazine, thiophene, bithiophene) is described. Crystal structures of the piperazine- and bithiophene-bridged diradicals have been determined by single-crystal X-ray diffraction. The two compounds are isostructural, belonging to the monoclinic space group P 2 1 / n; for the piperazine derivative a = 5.9913(6) Å, b = 19.1958(16) Å, c = 9.1244(6) Å, β = 100.314(7)°, and Z = 4. For the bithiophene derivative a = 5.9907(17) Å, b = 24.272(3) Å, c = 9.1740(14) Å, β = 102.961(18)°, and Z = 4. The diradicals associate as cofacial dimers which adopt a herringbone packing pattern analogous to that observed previously for the 1,4-phenylene-bridged derivative. In all three structures the herringbone arrays are characterized by a series of close interdimer S---S contacts along the spine. Consistently, the results of extended Hückel band structure calculations indicate highly developed two-dimensional electronic structures.