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 CuBr 2 , FeCl 3 , AuCl 3 , NbCl 5 , and CuCl 2 yield dark blue or black crystals of [TMO-TA] 2 [CuBr 4 ] ( 2 ), [TMO-TA][FeCl 4 ] · CH 3 CN ( 3 ), [TMO-TA][AuCl 4 ] ( 4 ), [TMO-TA][NbCl 6 ] · CH 3 CN ( 6 ), and [TMO-TA] 5 [Cu 2 Cl 6 ] 2 · 2 CH 3 CN ( 7 ). [TMO-TA] 2 [Ta 2 OF 10 ] ( 5 ) was obtained by anodic oxidation of TMO-TA in the presence of (Nbu 4 ) 2 [Ta 2 OF 10 ] as electrolyte. Using mercury(II) bromide, no redox reaction occurs. Instead, the colorless complex [HgBr 2 (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 Cu 2+ ions. Electrons on the organic radicals are strongly paired in all compounds.