5 3,3'-BRIDGED 2,2'-DITHIOPHENES

The crystal structures of the compounds 4H-cyclopenta-[2,1-b:3,4-b']di thiophene, C9H6S2 (I), penta[2,1-b:3,4-b']dithiophene-4,1'-cyclopentan e], C13H12S2 (II), 4H,6H-dithieno[3,2-c:2',3'-e]oxepine, C10H8OS2 (III ), drodithieno[3,2-g:2',3'-i][1,5]dioxacycloundecene, C13H14O2S2 (IV) and ithieno[3,2-i:2',3'-k][1,4,7]trioxacyclotridecene, C14H16O3S2 (V), have been determined at room temperature. For low values of the S-C-C -S torsion angle [(I), (II) and (III)], the C-C bond length between th e rings is ca 0.02 Angstrom shorter than the values found for (IV) and (V), where torsion angles are ca 90 degrees; this is in agreement wit h the change of the conjugation between the thiophene rings.