SINGLE-CRYSTAL STRUCTURE .107. STRUCTURAL -CHANGES IN THIANTHRENE, 2,3,6,7-TETRAMETHOXYTHIANTHRENE AND 2,3,6,7-TETRAMETHOXYSELENANTHRENE INCOMPLEXATION WITH ELECTRON-ACCEPTORS AND ONE-ELECTRON OXIDATION TO RADICAL CATIONS

Information on structural changes due to partial and full one-electron transfer is obtained by comparing the single crystal structures of bo th donor/acceptor complexes of thianthrene and selenanthrene derivativ es with those of their radical cation salts: The single crystal struct ures of {thianthrene ... pyromelliticdianhydride}, {2,3,6,7-tetrametho xythianthrene ... 1,2,4,5-tetracyanobenzene} and 2,3,6,7-tetramethoxys elenanthrene ... 1,2,4,5-tetracyanobenzene} do not exhibit any signifi cant differences relative to that of their components. On the contrary , in the corresponding radical cation salts [2,3,6,7-tetramethoxythian threne(.+)][Br-3(-)] as well as [2,3,6,7-tetramethoxyselenanthrene(.+) ][I-3(-)] severe structural changes are observed such as the flattenin g of the molecular skeletons or beginning cyanine distortions along th e chains H3CO-C-3-X-C-3-OCH3. Accompanying UV/VIS measurements of solu tions containing both donor and acceptor prove long-wavelengths charge transfer bands with drastically reduced excitation energies relative to that of the separated molecules. Therefore, in the ground state of the donor/acceptor complexes between electron-rich sulfur donors and s uitable accepters, only an almost negligible charge transfer occurs. T he weak interactions in the van der Waals complexes can be rationalize d by correlation of the respective orbital diagrams with the crystal l attice arrangements determined experimentally. Altogether, prospects f or new materials are provided.