Radical cations of chalcogenanthrenes with halogenido metalate anions. Part I: tetramethoxythianthrene

The electron-rich molecule tetramethoxythianthrene TMO-TA can readily be oxidized to the radical cation using various transition metal halides in acetonitrile as solvent. Reactions with CuBr2, FeCl3, AuCl3, NbCl5, and CuCl2 yield dark blue or black crystals of [TMO-TA]2[CuBr4] (2), [TMO-TA][FeCl4] · CH3CN (3), [TMO-TA][AuCl4] (4), [TMO-TA][NbCl6] · CH3CN (6), and [TMO-TA]5[Cu2Cl6]2 · 2 CH3CN (7). [TMO-TA]2[Ta2OF10] (5) was obtained by anodic oxidation of TMO-TA in the presence of (Nbu4)2[Ta2OF10] as electrolyte. Using mercury(II) bromide, no redox reaction occurs. Instead, the colorless complex [HgBr2(TMO-TA)] (1) is formed. In the crystal structures of the compounds 2–7, the almost planar radical cations show different types of arrangements. Pair formation of the [TMO-TA]•+ radicals to [TMO-TA]2 2+ dimers with the typical intra-pair S⋯S bonds of 3.1–3.2 Å lengths is predominant. Compounds 6 and 7 contain stacks of planar TMO-TA molecules in equidistant arrangement without pair formation and the unique feature of rotation of each adjacent cation by about 30°. Compounds 2, 5, and 7 are electrical semiconductors with band gaps between 0.62 and 1.4 eV, reflecting the arrangement of the radical cations. While 5 is diamagnetic, the magnetic momenta of 2 and 7 correspond only to the expected paramagnetic momenta of magnetically dilute Cu2+ ions. Electrons on the organic radicals are strongly paired in all compounds.